experiments in techniques of infrared...
TRANSCRIPT
990-9400
EXPERIMENTS IN TECHNIQUES OF INFRARED SPECTROSCOPY
by R W Hannah
J S Swinehart
PERKIN- ELMER
990-9400
EXPERIMENTS IN TECHNIQUES OF INFRARED SPECTROSCOPY
by
RW Hannah J S Swinehart
Perkin-Elmer Corporation Infrared Applications Laboratory
Rev September 1974
TABLE OF CONTENTS
Introduction bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull Instrumentation bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull ii Qualitative Analysis 11
Quantitative Analysis bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull iii Variation of Spectra with Structure and Composition bullbull iii Interpretation of Infrared Spectra bull bull bull bull bull bull bull bull bull bull bull bull bull vi References bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull xii
Experiment 1 - Instrument Operation and Calibration bullbullbull bull 1-1
Experiment 2 - Care and Handling of NaC1 and KBr Crystal Windows 2-1
Experiment 3 - Determining the Thickness of a Sealed Cell and of a Polymer Film bull bull bull bull bull bull bull bull bull bull bull bull bull bull 3- 1
Experiment 4 - Spectra of Pure Liquids bull bull bull bull bull bull bull bull bull bull bull bull bull 4- 1
Experiment 5 - Spectra of Liquids and Solids in Solution bullbullbullbullbullbullbullbull 5- 1
Experiment 6 Spectrum of a Solid and Preparation of a Mull 6-1
Experiment 7 - Spectra of Solids - the KBr Disc Technique bull bull bull 7-1
Experiment 8 - Spectrum of a Solid Prepared as a Film from Solution bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 1
Experiment 9 - Quantitative Analysis 9-1
Appendix 1 - Absorption in Different Regions of the Infrared Spectrum Al-l
NRC Bulletin No 6 - Infrared Spectra of Organic Compounds Summary Charts of Principal Group Frequencies
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1 The electromagnetic spectrum i
2 Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene i v
3 Types of vibrations bullbullbullbullbullbullbullbullbullbullbullbullbullbull iv
4 Absorption in different regions of the spectrum vi
5 Infrared absorption spectrum of C H 0 in a 0025S 12rom cell bullbullbullbullbullbullbullbullbullbull ix
6 Infrared absorption spectrum of a liquid with a molecular weight of 84 run in a 0025 rom cell x
LIST OF ILLUSTRATIONS
Figure
7 Infrared absorption spectrum of C H 0Cl in a 00258 7rom cell xi
1-1 IO baselinebullbullbullbullbullbullbullbull 1-2
1-2 Polystyrene calibration sample spectrum (005 rom film) 1-3
2-1 Correct way to polish crystal materials for infrared sample cells bullbullbullbullbullbullbullbullbullbullbullbullbull 2-3
2-2a Spectrum of clean sodium chloride window 4 rom thick 2-3
2-2b Spectrum of clean potassium bromide window 4 rom thick bull 2-4
2-3 spectrum of 4 rom thick sodium chloride window with residual Linde type 005 B Alumina polishing compound bullbull 2-4
2-4 Cleaving a sodium chloride crystal bullbullbullbullbullbull 2-5
-2-5 Cleavage planes of a crystal window bullbullbullbullbullbullbullbullbull 2-5
3-1 Path of radiation between the inner surface of a film or cell bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 3-2
3-2 Wave patterns for transmitted and reflected portions of radiation when cell thickness d is such that 2d = mA the in-phase condition for a fringe maximumbullbullbullbullbullbullbullbull 3-2
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LIST OF ILLUSTRATIONS (CONTID)
Figure
3-3 Fringe pattern obtained for an empty 01 mm thick
4- 8 Spectrum of mineral oil capillary film run in
4-9 Spectrum of perfluorohydrocarbon oil capillary film run in
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sealed KBr cell bull bull bull bull 3- 3
3-4 Fringe pattern obtained with the 005 rnrn thick polyshystyrene calibration sample bullbullbullbullbullbullbullbull bullbullbullbullbull 3-4
4- 1 Cor rect way to fill a sealed cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 2
4- 2 Carbon tetrachloride spectrum O 1 rnrn sealed cell bull bull bull bull 4- 2
4- 3 Carbon tetrachloride spectrum of reduced intensity becaus e of bubbles in sealed cell (0 1 mm sealed cell) bullbullbullbullbullbullbullbull 4-3
4-4 Use of two syringes to clean cells less than 0075 mm thick bull 4-3
4- 5 Carbon disulfide spectrum O 1 rnrn sealed cell bull bull bull bull bull 4- 4
4-6 Demountable cell assembly diagram bullbull bull bull bull bull bull bullbullbull 4-4
4-7 Indene spectrum 005 rnrn demountable cell bullbullbullbullbullbullbullbullbullbull 4-6
demountable cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 6
demountable cellbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 4-6
4-10 Spectrum of silicone grease smear run in demountable cell bull 4-7
5- 1 Spectrum of pure toluene run in 0025 mm sealed cell bullbullbull 5- 3
5- 2 Spectrum of 20 weight-to-volume polystyrene in xylene run in a 0025 mm demountable cell bullbullbullbullbullbullbullbull 5-4
6- I Spectrum of talc mulled in mineral oil bullbullbullbullbullbullbullbull 6- 2
6-2 Typical band distortion resulting from Christiansen scattering bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull 6- 3
6- 3 Spectrum of 24- dinitrophenylhydrazine mull bullbullbullbullbullbullbullbullbullbullbull 6- 4
6-4 Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering bull bull bull bull bull bull bull bullbull 6- 4
6- 5 Spectrum of phthalic anhydride mulled in perfluorohydrocarbon bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 6- 5
LIST OF ILLUSTRATIONS (CONTD)
Figure
6-6 Spectrum of phthalic anhydride mulled in mineral oil 6-5
9-2 A second example of an absorption band recorded on a linear
9-3 10 for complex absorption bands Dotted lines show extenshy
9-5 Spectrum of neat 2 - isopropyl alcohol in a 0015 mm KBr
9-6 Spectrum of neat methyl ethyl ketone in a 0015 mm KBr
9-7 Spectrum of solution containing 15 isopropyl alcohol 55
9-8 Spectrum of solution containing 20 isopropyl alcohol 45
9-9 Spectrum of solution containing 25 isopropyl alcohol 44
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6-7 Spectrum of sodium bicarbonate mulled in mineral oil bullbullbull 6-6
7-1 Spectrum of potassium bromide disc blank bullbullbullbullbullbullbull 7-2
7-2 Spectrum of benzoic acid in potassium bromide disc 7-3
7 - 3 Spectrum of benzoic acid in potassium bromide disc showing band distortions caused by poor grinding 7-3
7-4 Spectrum of quartz in potassium bromide disc 7-3
8- 1 Spectrum of polystyrene cast film bullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 2
9-1 Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale 9-2
transmittance scale and on a nonlinear absorbance scale 9-2
sion of bands in an assumed symmetrical Lorentzian 9-4
9-4 Spectrum of neat toluene in a O 015 mm KBr cell 9-5
cell 9-5
cell 9-6
toluene and 3000 methyl ketone in a 0025 mm cell 9-6
toluene and 35 methyl ethyl ketone in a 0025 mm cell 9-6
toluene and 31 methyl ethyl ketone in a 0025 mm cell 9-7
LIST OF ILLUSTRATIONS
Figure
9-10 Spectrum of solution containing 3500 isopropyl alcohol 20 toluene and 45 methyl ethyl ketone in a 0025 mm cell 9-7
9-11 Spectrum of solution containing 50 isopropyl alcohol 14 toluene and 36 methyl ethyl ketone in a 0025 mm cell 9-7
9-12 Plot of volume percent isopropyl alcohol vs absorbance obtained from 817 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-13 Plot of volume percent toluene vs asorbance obtained from 695 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-14 Semilog plot of percent T vs volume percent isopropyl alcohol as obtained from 817 em-1 absorption bands in Figs 9-7 through 9-11 9-9
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INTRODUCTION
Note The experiments described in this manual are intended to be to aid operators in learning the operation of infrared instrushy
mentation and the basic techniques of sample handling Though they are written for the Perkin-Elmer Model 735 infrared spectrophotoshymeter they may be applied to any infrared instrument by extrapolashytion with the specifications of that specific instrument
Infrared is the portion of the electromagnetic spectrum that extends beyond the visible into the microwave region (Fig 1) It is measured in units of frequency or wavelength In the infrared frequency is usually expressed in wavenumber units or reciprocal centimeters (cm- l) which are the number of waves fer centimeter Wavelength is expressed in microns (10- 3 mm or 10- cm) abbreviated Frequency f and waveshylength A are related by the equation fA bull c where fre~uency is defined as cycles per second and c is the velocity of light 3 x 10 0 cmsec A wavenumber unit v is defined as the reciprocal of wavelength (v bull 104 A) The product of v and c gives the frequency in cyclessec The infrared region extends from approximately 075 JJ to almost 1 mm but the segment most often used by the chemist is from 4000 to 400 cm- l (25 to 25 JJ) termed the fundamental region The low frequency region from 600 cm-1 to 200 cm- l the extended range and the range from 200 cm- l to the microwave region are often called the far infrared The region from 4000 cm-1 to the visible is often called the near infrared or overtone region
All molecules are made up of atoms held together by chemical bonds These atoms vibrate with respect to each other the bonds acting much like springs connecting the atoms Each molecule has its own specific set of vibrational frequencies but different molecules have different sets of vibrations The frequencies of these vibrations are in the same range as the infrared frequencies of electromagnetic radiation
Vfavemunber 10 13 10 10 108 10middot 25105 142 105 4000 650 12 smiddot lO~ 10- 3 10- 6
em-l
lO~7Energy lfiI 1~6 1 102 15 0 7 1O~2 1510- 3 S--lO~6 10- 10
lectron volta
Z5 154 830
Fig 1 - The electromagnetic spectrum
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Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
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spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
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H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
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mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
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FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
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Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
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I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
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FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
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FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
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REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
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Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
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Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
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Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
990-9400
EXPERIMENTS IN TECHNIQUES OF INFRARED SPECTROSCOPY
by
RW Hannah J S Swinehart
Perkin-Elmer Corporation Infrared Applications Laboratory
Rev September 1974
TABLE OF CONTENTS
Introduction bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull Instrumentation bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull ii Qualitative Analysis 11
Quantitative Analysis bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull iii Variation of Spectra with Structure and Composition bullbull iii Interpretation of Infrared Spectra bull bull bull bull bull bull bull bull bull bull bull bull bull vi References bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull xii
Experiment 1 - Instrument Operation and Calibration bullbullbull bull 1-1
Experiment 2 - Care and Handling of NaC1 and KBr Crystal Windows 2-1
Experiment 3 - Determining the Thickness of a Sealed Cell and of a Polymer Film bull bull bull bull bull bull bull bull bull bull bull bull bull bull 3- 1
Experiment 4 - Spectra of Pure Liquids bull bull bull bull bull bull bull bull bull bull bull bull bull 4- 1
Experiment 5 - Spectra of Liquids and Solids in Solution bullbullbullbullbullbullbullbull 5- 1
Experiment 6 Spectrum of a Solid and Preparation of a Mull 6-1
Experiment 7 - Spectra of Solids - the KBr Disc Technique bull bull bull 7-1
Experiment 8 - Spectrum of a Solid Prepared as a Film from Solution bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 1
Experiment 9 - Quantitative Analysis 9-1
Appendix 1 - Absorption in Different Regions of the Infrared Spectrum Al-l
NRC Bulletin No 6 - Infrared Spectra of Organic Compounds Summary Charts of Principal Group Frequencies
974
1 The electromagnetic spectrum i
2 Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene i v
3 Types of vibrations bullbullbullbullbullbullbullbullbullbullbullbullbullbull iv
4 Absorption in different regions of the spectrum vi
5 Infrared absorption spectrum of C H 0 in a 0025S 12rom cell bullbullbullbullbullbullbullbullbullbull ix
6 Infrared absorption spectrum of a liquid with a molecular weight of 84 run in a 0025 rom cell x
LIST OF ILLUSTRATIONS
Figure
7 Infrared absorption spectrum of C H 0Cl in a 00258 7rom cell xi
1-1 IO baselinebullbullbullbullbullbullbullbull 1-2
1-2 Polystyrene calibration sample spectrum (005 rom film) 1-3
2-1 Correct way to polish crystal materials for infrared sample cells bullbullbullbullbullbullbullbullbullbullbullbullbull 2-3
2-2a Spectrum of clean sodium chloride window 4 rom thick 2-3
2-2b Spectrum of clean potassium bromide window 4 rom thick bull 2-4
2-3 spectrum of 4 rom thick sodium chloride window with residual Linde type 005 B Alumina polishing compound bullbull 2-4
2-4 Cleaving a sodium chloride crystal bullbullbullbullbullbull 2-5
-2-5 Cleavage planes of a crystal window bullbullbullbullbullbullbullbullbull 2-5
3-1 Path of radiation between the inner surface of a film or cell bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 3-2
3-2 Wave patterns for transmitted and reflected portions of radiation when cell thickness d is such that 2d = mA the in-phase condition for a fringe maximumbullbullbullbullbullbullbullbull 3-2
974
LIST OF ILLUSTRATIONS (CONTID)
Figure
3-3 Fringe pattern obtained for an empty 01 mm thick
4- 8 Spectrum of mineral oil capillary film run in
4-9 Spectrum of perfluorohydrocarbon oil capillary film run in
974
sealed KBr cell bull bull bull bull 3- 3
3-4 Fringe pattern obtained with the 005 rnrn thick polyshystyrene calibration sample bullbullbullbullbullbullbullbull bullbullbullbullbull 3-4
4- 1 Cor rect way to fill a sealed cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 2
4- 2 Carbon tetrachloride spectrum O 1 rnrn sealed cell bull bull bull bull 4- 2
4- 3 Carbon tetrachloride spectrum of reduced intensity becaus e of bubbles in sealed cell (0 1 mm sealed cell) bullbullbullbullbullbullbullbull 4-3
4-4 Use of two syringes to clean cells less than 0075 mm thick bull 4-3
4- 5 Carbon disulfide spectrum O 1 rnrn sealed cell bull bull bull bull bull 4- 4
4-6 Demountable cell assembly diagram bullbull bull bull bull bull bull bullbullbull 4-4
4-7 Indene spectrum 005 rnrn demountable cell bullbullbullbullbullbullbullbullbullbull 4-6
demountable cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 6
demountable cellbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 4-6
4-10 Spectrum of silicone grease smear run in demountable cell bull 4-7
5- 1 Spectrum of pure toluene run in 0025 mm sealed cell bullbullbull 5- 3
5- 2 Spectrum of 20 weight-to-volume polystyrene in xylene run in a 0025 mm demountable cell bullbullbullbullbullbullbullbull 5-4
6- I Spectrum of talc mulled in mineral oil bullbullbullbullbullbullbullbull 6- 2
6-2 Typical band distortion resulting from Christiansen scattering bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull 6- 3
6- 3 Spectrum of 24- dinitrophenylhydrazine mull bullbullbullbullbullbullbullbullbullbullbull 6- 4
6-4 Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering bull bull bull bull bull bull bull bullbull 6- 4
6- 5 Spectrum of phthalic anhydride mulled in perfluorohydrocarbon bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 6- 5
LIST OF ILLUSTRATIONS (CONTD)
Figure
6-6 Spectrum of phthalic anhydride mulled in mineral oil 6-5
9-2 A second example of an absorption band recorded on a linear
9-3 10 for complex absorption bands Dotted lines show extenshy
9-5 Spectrum of neat 2 - isopropyl alcohol in a 0015 mm KBr
9-6 Spectrum of neat methyl ethyl ketone in a 0015 mm KBr
9-7 Spectrum of solution containing 15 isopropyl alcohol 55
9-8 Spectrum of solution containing 20 isopropyl alcohol 45
9-9 Spectrum of solution containing 25 isopropyl alcohol 44
974
6-7 Spectrum of sodium bicarbonate mulled in mineral oil bullbullbull 6-6
7-1 Spectrum of potassium bromide disc blank bullbullbullbullbullbullbull 7-2
7-2 Spectrum of benzoic acid in potassium bromide disc 7-3
7 - 3 Spectrum of benzoic acid in potassium bromide disc showing band distortions caused by poor grinding 7-3
7-4 Spectrum of quartz in potassium bromide disc 7-3
8- 1 Spectrum of polystyrene cast film bullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 2
9-1 Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale 9-2
transmittance scale and on a nonlinear absorbance scale 9-2
sion of bands in an assumed symmetrical Lorentzian 9-4
9-4 Spectrum of neat toluene in a O 015 mm KBr cell 9-5
cell 9-5
cell 9-6
toluene and 3000 methyl ketone in a 0025 mm cell 9-6
toluene and 35 methyl ethyl ketone in a 0025 mm cell 9-6
toluene and 31 methyl ethyl ketone in a 0025 mm cell 9-7
LIST OF ILLUSTRATIONS
Figure
9-10 Spectrum of solution containing 3500 isopropyl alcohol 20 toluene and 45 methyl ethyl ketone in a 0025 mm cell 9-7
9-11 Spectrum of solution containing 50 isopropyl alcohol 14 toluene and 36 methyl ethyl ketone in a 0025 mm cell 9-7
9-12 Plot of volume percent isopropyl alcohol vs absorbance obtained from 817 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-13 Plot of volume percent toluene vs asorbance obtained from 695 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-14 Semilog plot of percent T vs volume percent isopropyl alcohol as obtained from 817 em-1 absorption bands in Figs 9-7 through 9-11 9-9
974
INTRODUCTION
Note The experiments described in this manual are intended to be to aid operators in learning the operation of infrared instrushy
mentation and the basic techniques of sample handling Though they are written for the Perkin-Elmer Model 735 infrared spectrophotoshymeter they may be applied to any infrared instrument by extrapolashytion with the specifications of that specific instrument
Infrared is the portion of the electromagnetic spectrum that extends beyond the visible into the microwave region (Fig 1) It is measured in units of frequency or wavelength In the infrared frequency is usually expressed in wavenumber units or reciprocal centimeters (cm- l) which are the number of waves fer centimeter Wavelength is expressed in microns (10- 3 mm or 10- cm) abbreviated Frequency f and waveshylength A are related by the equation fA bull c where fre~uency is defined as cycles per second and c is the velocity of light 3 x 10 0 cmsec A wavenumber unit v is defined as the reciprocal of wavelength (v bull 104 A) The product of v and c gives the frequency in cyclessec The infrared region extends from approximately 075 JJ to almost 1 mm but the segment most often used by the chemist is from 4000 to 400 cm- l (25 to 25 JJ) termed the fundamental region The low frequency region from 600 cm-1 to 200 cm- l the extended range and the range from 200 cm- l to the microwave region are often called the far infrared The region from 4000 cm-1 to the visible is often called the near infrared or overtone region
All molecules are made up of atoms held together by chemical bonds These atoms vibrate with respect to each other the bonds acting much like springs connecting the atoms Each molecule has its own specific set of vibrational frequencies but different molecules have different sets of vibrations The frequencies of these vibrations are in the same range as the infrared frequencies of electromagnetic radiation
Vfavemunber 10 13 10 10 108 10middot 25105 142 105 4000 650 12 smiddot lO~ 10- 3 10- 6
em-l
lO~7Energy lfiI 1~6 1 102 15 0 7 1O~2 1510- 3 S--lO~6 10- 10
lectron volta
Z5 154 830
Fig 1 - The electromagnetic spectrum
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ii
Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
974
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
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iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
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0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
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FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
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Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
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I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
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FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
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It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
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REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
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Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
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Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
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Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
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Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
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Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
TABLE OF CONTENTS
Introduction bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull Instrumentation bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull ii Qualitative Analysis 11
Quantitative Analysis bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull iii Variation of Spectra with Structure and Composition bullbull iii Interpretation of Infrared Spectra bull bull bull bull bull bull bull bull bull bull bull bull bull vi References bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull xii
Experiment 1 - Instrument Operation and Calibration bullbullbull bull 1-1
Experiment 2 - Care and Handling of NaC1 and KBr Crystal Windows 2-1
Experiment 3 - Determining the Thickness of a Sealed Cell and of a Polymer Film bull bull bull bull bull bull bull bull bull bull bull bull bull bull 3- 1
Experiment 4 - Spectra of Pure Liquids bull bull bull bull bull bull bull bull bull bull bull bull bull 4- 1
Experiment 5 - Spectra of Liquids and Solids in Solution bullbullbullbullbullbullbullbull 5- 1
Experiment 6 Spectrum of a Solid and Preparation of a Mull 6-1
Experiment 7 - Spectra of Solids - the KBr Disc Technique bull bull bull 7-1
Experiment 8 - Spectrum of a Solid Prepared as a Film from Solution bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 1
Experiment 9 - Quantitative Analysis 9-1
Appendix 1 - Absorption in Different Regions of the Infrared Spectrum Al-l
NRC Bulletin No 6 - Infrared Spectra of Organic Compounds Summary Charts of Principal Group Frequencies
974
1 The electromagnetic spectrum i
2 Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene i v
3 Types of vibrations bullbullbullbullbullbullbullbullbullbullbullbullbullbull iv
4 Absorption in different regions of the spectrum vi
5 Infrared absorption spectrum of C H 0 in a 0025S 12rom cell bullbullbullbullbullbullbullbullbullbull ix
6 Infrared absorption spectrum of a liquid with a molecular weight of 84 run in a 0025 rom cell x
LIST OF ILLUSTRATIONS
Figure
7 Infrared absorption spectrum of C H 0Cl in a 00258 7rom cell xi
1-1 IO baselinebullbullbullbullbullbullbullbull 1-2
1-2 Polystyrene calibration sample spectrum (005 rom film) 1-3
2-1 Correct way to polish crystal materials for infrared sample cells bullbullbullbullbullbullbullbullbullbullbullbullbull 2-3
2-2a Spectrum of clean sodium chloride window 4 rom thick 2-3
2-2b Spectrum of clean potassium bromide window 4 rom thick bull 2-4
2-3 spectrum of 4 rom thick sodium chloride window with residual Linde type 005 B Alumina polishing compound bullbull 2-4
2-4 Cleaving a sodium chloride crystal bullbullbullbullbullbull 2-5
-2-5 Cleavage planes of a crystal window bullbullbullbullbullbullbullbullbull 2-5
3-1 Path of radiation between the inner surface of a film or cell bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 3-2
3-2 Wave patterns for transmitted and reflected portions of radiation when cell thickness d is such that 2d = mA the in-phase condition for a fringe maximumbullbullbullbullbullbullbullbull 3-2
974
LIST OF ILLUSTRATIONS (CONTID)
Figure
3-3 Fringe pattern obtained for an empty 01 mm thick
4- 8 Spectrum of mineral oil capillary film run in
4-9 Spectrum of perfluorohydrocarbon oil capillary film run in
974
sealed KBr cell bull bull bull bull 3- 3
3-4 Fringe pattern obtained with the 005 rnrn thick polyshystyrene calibration sample bullbullbullbullbullbullbullbull bullbullbullbullbull 3-4
4- 1 Cor rect way to fill a sealed cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 2
4- 2 Carbon tetrachloride spectrum O 1 rnrn sealed cell bull bull bull bull 4- 2
4- 3 Carbon tetrachloride spectrum of reduced intensity becaus e of bubbles in sealed cell (0 1 mm sealed cell) bullbullbullbullbullbullbullbull 4-3
4-4 Use of two syringes to clean cells less than 0075 mm thick bull 4-3
4- 5 Carbon disulfide spectrum O 1 rnrn sealed cell bull bull bull bull bull 4- 4
4-6 Demountable cell assembly diagram bullbull bull bull bull bull bull bullbullbull 4-4
4-7 Indene spectrum 005 rnrn demountable cell bullbullbullbullbullbullbullbullbullbull 4-6
demountable cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 6
demountable cellbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 4-6
4-10 Spectrum of silicone grease smear run in demountable cell bull 4-7
5- 1 Spectrum of pure toluene run in 0025 mm sealed cell bullbullbull 5- 3
5- 2 Spectrum of 20 weight-to-volume polystyrene in xylene run in a 0025 mm demountable cell bullbullbullbullbullbullbullbull 5-4
6- I Spectrum of talc mulled in mineral oil bullbullbullbullbullbullbullbull 6- 2
6-2 Typical band distortion resulting from Christiansen scattering bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull 6- 3
6- 3 Spectrum of 24- dinitrophenylhydrazine mull bullbullbullbullbullbullbullbullbullbullbull 6- 4
6-4 Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering bull bull bull bull bull bull bull bullbull 6- 4
6- 5 Spectrum of phthalic anhydride mulled in perfluorohydrocarbon bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 6- 5
LIST OF ILLUSTRATIONS (CONTD)
Figure
6-6 Spectrum of phthalic anhydride mulled in mineral oil 6-5
9-2 A second example of an absorption band recorded on a linear
9-3 10 for complex absorption bands Dotted lines show extenshy
9-5 Spectrum of neat 2 - isopropyl alcohol in a 0015 mm KBr
9-6 Spectrum of neat methyl ethyl ketone in a 0015 mm KBr
9-7 Spectrum of solution containing 15 isopropyl alcohol 55
9-8 Spectrum of solution containing 20 isopropyl alcohol 45
9-9 Spectrum of solution containing 25 isopropyl alcohol 44
974
6-7 Spectrum of sodium bicarbonate mulled in mineral oil bullbullbull 6-6
7-1 Spectrum of potassium bromide disc blank bullbullbullbullbullbullbull 7-2
7-2 Spectrum of benzoic acid in potassium bromide disc 7-3
7 - 3 Spectrum of benzoic acid in potassium bromide disc showing band distortions caused by poor grinding 7-3
7-4 Spectrum of quartz in potassium bromide disc 7-3
8- 1 Spectrum of polystyrene cast film bullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 2
9-1 Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale 9-2
transmittance scale and on a nonlinear absorbance scale 9-2
sion of bands in an assumed symmetrical Lorentzian 9-4
9-4 Spectrum of neat toluene in a O 015 mm KBr cell 9-5
cell 9-5
cell 9-6
toluene and 3000 methyl ketone in a 0025 mm cell 9-6
toluene and 35 methyl ethyl ketone in a 0025 mm cell 9-6
toluene and 31 methyl ethyl ketone in a 0025 mm cell 9-7
LIST OF ILLUSTRATIONS
Figure
9-10 Spectrum of solution containing 3500 isopropyl alcohol 20 toluene and 45 methyl ethyl ketone in a 0025 mm cell 9-7
9-11 Spectrum of solution containing 50 isopropyl alcohol 14 toluene and 36 methyl ethyl ketone in a 0025 mm cell 9-7
9-12 Plot of volume percent isopropyl alcohol vs absorbance obtained from 817 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-13 Plot of volume percent toluene vs asorbance obtained from 695 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-14 Semilog plot of percent T vs volume percent isopropyl alcohol as obtained from 817 em-1 absorption bands in Figs 9-7 through 9-11 9-9
974
INTRODUCTION
Note The experiments described in this manual are intended to be to aid operators in learning the operation of infrared instrushy
mentation and the basic techniques of sample handling Though they are written for the Perkin-Elmer Model 735 infrared spectrophotoshymeter they may be applied to any infrared instrument by extrapolashytion with the specifications of that specific instrument
Infrared is the portion of the electromagnetic spectrum that extends beyond the visible into the microwave region (Fig 1) It is measured in units of frequency or wavelength In the infrared frequency is usually expressed in wavenumber units or reciprocal centimeters (cm- l) which are the number of waves fer centimeter Wavelength is expressed in microns (10- 3 mm or 10- cm) abbreviated Frequency f and waveshylength A are related by the equation fA bull c where fre~uency is defined as cycles per second and c is the velocity of light 3 x 10 0 cmsec A wavenumber unit v is defined as the reciprocal of wavelength (v bull 104 A) The product of v and c gives the frequency in cyclessec The infrared region extends from approximately 075 JJ to almost 1 mm but the segment most often used by the chemist is from 4000 to 400 cm- l (25 to 25 JJ) termed the fundamental region The low frequency region from 600 cm-1 to 200 cm- l the extended range and the range from 200 cm- l to the microwave region are often called the far infrared The region from 4000 cm-1 to the visible is often called the near infrared or overtone region
All molecules are made up of atoms held together by chemical bonds These atoms vibrate with respect to each other the bonds acting much like springs connecting the atoms Each molecule has its own specific set of vibrational frequencies but different molecules have different sets of vibrations The frequencies of these vibrations are in the same range as the infrared frequencies of electromagnetic radiation
Vfavemunber 10 13 10 10 108 10middot 25105 142 105 4000 650 12 smiddot lO~ 10- 3 10- 6
em-l
lO~7Energy lfiI 1~6 1 102 15 0 7 1O~2 1510- 3 S--lO~6 10- 10
lectron volta
Z5 154 830
Fig 1 - The electromagnetic spectrum
974
ii
Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
974
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
974
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
974
0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
xi
FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
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Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
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Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
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Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
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Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
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Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
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Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
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Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
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Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
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7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
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Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
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Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
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Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
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Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
1 The electromagnetic spectrum i
2 Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene i v
3 Types of vibrations bullbullbullbullbullbullbullbullbullbullbullbullbullbull iv
4 Absorption in different regions of the spectrum vi
5 Infrared absorption spectrum of C H 0 in a 0025S 12rom cell bullbullbullbullbullbullbullbullbullbull ix
6 Infrared absorption spectrum of a liquid with a molecular weight of 84 run in a 0025 rom cell x
LIST OF ILLUSTRATIONS
Figure
7 Infrared absorption spectrum of C H 0Cl in a 00258 7rom cell xi
1-1 IO baselinebullbullbullbullbullbullbullbull 1-2
1-2 Polystyrene calibration sample spectrum (005 rom film) 1-3
2-1 Correct way to polish crystal materials for infrared sample cells bullbullbullbullbullbullbullbullbullbullbullbullbull 2-3
2-2a Spectrum of clean sodium chloride window 4 rom thick 2-3
2-2b Spectrum of clean potassium bromide window 4 rom thick bull 2-4
2-3 spectrum of 4 rom thick sodium chloride window with residual Linde type 005 B Alumina polishing compound bullbull 2-4
2-4 Cleaving a sodium chloride crystal bullbullbullbullbullbull 2-5
-2-5 Cleavage planes of a crystal window bullbullbullbullbullbullbullbullbull 2-5
3-1 Path of radiation between the inner surface of a film or cell bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 3-2
3-2 Wave patterns for transmitted and reflected portions of radiation when cell thickness d is such that 2d = mA the in-phase condition for a fringe maximumbullbullbullbullbullbullbullbull 3-2
974
LIST OF ILLUSTRATIONS (CONTID)
Figure
3-3 Fringe pattern obtained for an empty 01 mm thick
4- 8 Spectrum of mineral oil capillary film run in
4-9 Spectrum of perfluorohydrocarbon oil capillary film run in
974
sealed KBr cell bull bull bull bull 3- 3
3-4 Fringe pattern obtained with the 005 rnrn thick polyshystyrene calibration sample bullbullbullbullbullbullbullbull bullbullbullbullbull 3-4
4- 1 Cor rect way to fill a sealed cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 2
4- 2 Carbon tetrachloride spectrum O 1 rnrn sealed cell bull bull bull bull 4- 2
4- 3 Carbon tetrachloride spectrum of reduced intensity becaus e of bubbles in sealed cell (0 1 mm sealed cell) bullbullbullbullbullbullbullbull 4-3
4-4 Use of two syringes to clean cells less than 0075 mm thick bull 4-3
4- 5 Carbon disulfide spectrum O 1 rnrn sealed cell bull bull bull bull bull 4- 4
4-6 Demountable cell assembly diagram bullbull bull bull bull bull bull bullbullbull 4-4
4-7 Indene spectrum 005 rnrn demountable cell bullbullbullbullbullbullbullbullbullbull 4-6
demountable cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 6
demountable cellbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 4-6
4-10 Spectrum of silicone grease smear run in demountable cell bull 4-7
5- 1 Spectrum of pure toluene run in 0025 mm sealed cell bullbullbull 5- 3
5- 2 Spectrum of 20 weight-to-volume polystyrene in xylene run in a 0025 mm demountable cell bullbullbullbullbullbullbullbull 5-4
6- I Spectrum of talc mulled in mineral oil bullbullbullbullbullbullbullbull 6- 2
6-2 Typical band distortion resulting from Christiansen scattering bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull 6- 3
6- 3 Spectrum of 24- dinitrophenylhydrazine mull bullbullbullbullbullbullbullbullbullbullbull 6- 4
6-4 Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering bull bull bull bull bull bull bull bullbull 6- 4
6- 5 Spectrum of phthalic anhydride mulled in perfluorohydrocarbon bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 6- 5
LIST OF ILLUSTRATIONS (CONTD)
Figure
6-6 Spectrum of phthalic anhydride mulled in mineral oil 6-5
9-2 A second example of an absorption band recorded on a linear
9-3 10 for complex absorption bands Dotted lines show extenshy
9-5 Spectrum of neat 2 - isopropyl alcohol in a 0015 mm KBr
9-6 Spectrum of neat methyl ethyl ketone in a 0015 mm KBr
9-7 Spectrum of solution containing 15 isopropyl alcohol 55
9-8 Spectrum of solution containing 20 isopropyl alcohol 45
9-9 Spectrum of solution containing 25 isopropyl alcohol 44
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6-7 Spectrum of sodium bicarbonate mulled in mineral oil bullbullbull 6-6
7-1 Spectrum of potassium bromide disc blank bullbullbullbullbullbullbull 7-2
7-2 Spectrum of benzoic acid in potassium bromide disc 7-3
7 - 3 Spectrum of benzoic acid in potassium bromide disc showing band distortions caused by poor grinding 7-3
7-4 Spectrum of quartz in potassium bromide disc 7-3
8- 1 Spectrum of polystyrene cast film bullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 2
9-1 Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale 9-2
transmittance scale and on a nonlinear absorbance scale 9-2
sion of bands in an assumed symmetrical Lorentzian 9-4
9-4 Spectrum of neat toluene in a O 015 mm KBr cell 9-5
cell 9-5
cell 9-6
toluene and 3000 methyl ketone in a 0025 mm cell 9-6
toluene and 35 methyl ethyl ketone in a 0025 mm cell 9-6
toluene and 31 methyl ethyl ketone in a 0025 mm cell 9-7
LIST OF ILLUSTRATIONS
Figure
9-10 Spectrum of solution containing 3500 isopropyl alcohol 20 toluene and 45 methyl ethyl ketone in a 0025 mm cell 9-7
9-11 Spectrum of solution containing 50 isopropyl alcohol 14 toluene and 36 methyl ethyl ketone in a 0025 mm cell 9-7
9-12 Plot of volume percent isopropyl alcohol vs absorbance obtained from 817 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-13 Plot of volume percent toluene vs asorbance obtained from 695 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-14 Semilog plot of percent T vs volume percent isopropyl alcohol as obtained from 817 em-1 absorption bands in Figs 9-7 through 9-11 9-9
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INTRODUCTION
Note The experiments described in this manual are intended to be to aid operators in learning the operation of infrared instrushy
mentation and the basic techniques of sample handling Though they are written for the Perkin-Elmer Model 735 infrared spectrophotoshymeter they may be applied to any infrared instrument by extrapolashytion with the specifications of that specific instrument
Infrared is the portion of the electromagnetic spectrum that extends beyond the visible into the microwave region (Fig 1) It is measured in units of frequency or wavelength In the infrared frequency is usually expressed in wavenumber units or reciprocal centimeters (cm- l) which are the number of waves fer centimeter Wavelength is expressed in microns (10- 3 mm or 10- cm) abbreviated Frequency f and waveshylength A are related by the equation fA bull c where fre~uency is defined as cycles per second and c is the velocity of light 3 x 10 0 cmsec A wavenumber unit v is defined as the reciprocal of wavelength (v bull 104 A) The product of v and c gives the frequency in cyclessec The infrared region extends from approximately 075 JJ to almost 1 mm but the segment most often used by the chemist is from 4000 to 400 cm- l (25 to 25 JJ) termed the fundamental region The low frequency region from 600 cm-1 to 200 cm- l the extended range and the range from 200 cm- l to the microwave region are often called the far infrared The region from 4000 cm-1 to the visible is often called the near infrared or overtone region
All molecules are made up of atoms held together by chemical bonds These atoms vibrate with respect to each other the bonds acting much like springs connecting the atoms Each molecule has its own specific set of vibrational frequencies but different molecules have different sets of vibrations The frequencies of these vibrations are in the same range as the infrared frequencies of electromagnetic radiation
Vfavemunber 10 13 10 10 108 10middot 25105 142 105 4000 650 12 smiddot lO~ 10- 3 10- 6
em-l
lO~7Energy lfiI 1~6 1 102 15 0 7 1O~2 1510- 3 S--lO~6 10- 10
lectron volta
Z5 154 830
Fig 1 - The electromagnetic spectrum
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ii
Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
974
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
974
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
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0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
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vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
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vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
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viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
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FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
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It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
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xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
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Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
LIST OF ILLUSTRATIONS (CONTID)
Figure
3-3 Fringe pattern obtained for an empty 01 mm thick
4- 8 Spectrum of mineral oil capillary film run in
4-9 Spectrum of perfluorohydrocarbon oil capillary film run in
974
sealed KBr cell bull bull bull bull 3- 3
3-4 Fringe pattern obtained with the 005 rnrn thick polyshystyrene calibration sample bullbullbullbullbullbullbullbull bullbullbullbullbull 3-4
4- 1 Cor rect way to fill a sealed cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 2
4- 2 Carbon tetrachloride spectrum O 1 rnrn sealed cell bull bull bull bull 4- 2
4- 3 Carbon tetrachloride spectrum of reduced intensity becaus e of bubbles in sealed cell (0 1 mm sealed cell) bullbullbullbullbullbullbullbull 4-3
4-4 Use of two syringes to clean cells less than 0075 mm thick bull 4-3
4- 5 Carbon disulfide spectrum O 1 rnrn sealed cell bull bull bull bull bull 4- 4
4-6 Demountable cell assembly diagram bullbull bull bull bull bull bull bullbullbull 4-4
4-7 Indene spectrum 005 rnrn demountable cell bullbullbullbullbullbullbullbullbullbull 4-6
demountable cell bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bullbull 4- 6
demountable cellbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 4-6
4-10 Spectrum of silicone grease smear run in demountable cell bull 4-7
5- 1 Spectrum of pure toluene run in 0025 mm sealed cell bullbullbull 5- 3
5- 2 Spectrum of 20 weight-to-volume polystyrene in xylene run in a 0025 mm demountable cell bullbullbullbullbullbullbullbull 5-4
6- I Spectrum of talc mulled in mineral oil bullbullbullbullbullbullbullbull 6- 2
6-2 Typical band distortion resulting from Christiansen scattering bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull bull 6- 3
6- 3 Spectrum of 24- dinitrophenylhydrazine mull bullbullbullbullbullbullbullbullbullbullbull 6- 4
6-4 Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering bull bull bull bull bull bull bull bullbull 6- 4
6- 5 Spectrum of phthalic anhydride mulled in perfluorohydrocarbon bullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 6- 5
LIST OF ILLUSTRATIONS (CONTD)
Figure
6-6 Spectrum of phthalic anhydride mulled in mineral oil 6-5
9-2 A second example of an absorption band recorded on a linear
9-3 10 for complex absorption bands Dotted lines show extenshy
9-5 Spectrum of neat 2 - isopropyl alcohol in a 0015 mm KBr
9-6 Spectrum of neat methyl ethyl ketone in a 0015 mm KBr
9-7 Spectrum of solution containing 15 isopropyl alcohol 55
9-8 Spectrum of solution containing 20 isopropyl alcohol 45
9-9 Spectrum of solution containing 25 isopropyl alcohol 44
974
6-7 Spectrum of sodium bicarbonate mulled in mineral oil bullbullbull 6-6
7-1 Spectrum of potassium bromide disc blank bullbullbullbullbullbullbull 7-2
7-2 Spectrum of benzoic acid in potassium bromide disc 7-3
7 - 3 Spectrum of benzoic acid in potassium bromide disc showing band distortions caused by poor grinding 7-3
7-4 Spectrum of quartz in potassium bromide disc 7-3
8- 1 Spectrum of polystyrene cast film bullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 2
9-1 Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale 9-2
transmittance scale and on a nonlinear absorbance scale 9-2
sion of bands in an assumed symmetrical Lorentzian 9-4
9-4 Spectrum of neat toluene in a O 015 mm KBr cell 9-5
cell 9-5
cell 9-6
toluene and 3000 methyl ketone in a 0025 mm cell 9-6
toluene and 35 methyl ethyl ketone in a 0025 mm cell 9-6
toluene and 31 methyl ethyl ketone in a 0025 mm cell 9-7
LIST OF ILLUSTRATIONS
Figure
9-10 Spectrum of solution containing 3500 isopropyl alcohol 20 toluene and 45 methyl ethyl ketone in a 0025 mm cell 9-7
9-11 Spectrum of solution containing 50 isopropyl alcohol 14 toluene and 36 methyl ethyl ketone in a 0025 mm cell 9-7
9-12 Plot of volume percent isopropyl alcohol vs absorbance obtained from 817 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-13 Plot of volume percent toluene vs asorbance obtained from 695 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-14 Semilog plot of percent T vs volume percent isopropyl alcohol as obtained from 817 em-1 absorption bands in Figs 9-7 through 9-11 9-9
974
INTRODUCTION
Note The experiments described in this manual are intended to be to aid operators in learning the operation of infrared instrushy
mentation and the basic techniques of sample handling Though they are written for the Perkin-Elmer Model 735 infrared spectrophotoshymeter they may be applied to any infrared instrument by extrapolashytion with the specifications of that specific instrument
Infrared is the portion of the electromagnetic spectrum that extends beyond the visible into the microwave region (Fig 1) It is measured in units of frequency or wavelength In the infrared frequency is usually expressed in wavenumber units or reciprocal centimeters (cm- l) which are the number of waves fer centimeter Wavelength is expressed in microns (10- 3 mm or 10- cm) abbreviated Frequency f and waveshylength A are related by the equation fA bull c where fre~uency is defined as cycles per second and c is the velocity of light 3 x 10 0 cmsec A wavenumber unit v is defined as the reciprocal of wavelength (v bull 104 A) The product of v and c gives the frequency in cyclessec The infrared region extends from approximately 075 JJ to almost 1 mm but the segment most often used by the chemist is from 4000 to 400 cm- l (25 to 25 JJ) termed the fundamental region The low frequency region from 600 cm-1 to 200 cm- l the extended range and the range from 200 cm- l to the microwave region are often called the far infrared The region from 4000 cm-1 to the visible is often called the near infrared or overtone region
All molecules are made up of atoms held together by chemical bonds These atoms vibrate with respect to each other the bonds acting much like springs connecting the atoms Each molecule has its own specific set of vibrational frequencies but different molecules have different sets of vibrations The frequencies of these vibrations are in the same range as the infrared frequencies of electromagnetic radiation
Vfavemunber 10 13 10 10 108 10middot 25105 142 105 4000 650 12 smiddot lO~ 10- 3 10- 6
em-l
lO~7Energy lfiI 1~6 1 102 15 0 7 1O~2 1510- 3 S--lO~6 10- 10
lectron volta
Z5 154 830
Fig 1 - The electromagnetic spectrum
974
ii
Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
974
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
974
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
974
0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
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It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
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xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
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Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
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Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
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Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
LIST OF ILLUSTRATIONS (CONTD)
Figure
6-6 Spectrum of phthalic anhydride mulled in mineral oil 6-5
9-2 A second example of an absorption band recorded on a linear
9-3 10 for complex absorption bands Dotted lines show extenshy
9-5 Spectrum of neat 2 - isopropyl alcohol in a 0015 mm KBr
9-6 Spectrum of neat methyl ethyl ketone in a 0015 mm KBr
9-7 Spectrum of solution containing 15 isopropyl alcohol 55
9-8 Spectrum of solution containing 20 isopropyl alcohol 45
9-9 Spectrum of solution containing 25 isopropyl alcohol 44
974
6-7 Spectrum of sodium bicarbonate mulled in mineral oil bullbullbull 6-6
7-1 Spectrum of potassium bromide disc blank bullbullbullbullbullbullbull 7-2
7-2 Spectrum of benzoic acid in potassium bromide disc 7-3
7 - 3 Spectrum of benzoic acid in potassium bromide disc showing band distortions caused by poor grinding 7-3
7-4 Spectrum of quartz in potassium bromide disc 7-3
8- 1 Spectrum of polystyrene cast film bullbullbullbullbullbullbullbullbullbullbullbullbullbullbull 8- 2
9-1 Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale 9-2
transmittance scale and on a nonlinear absorbance scale 9-2
sion of bands in an assumed symmetrical Lorentzian 9-4
9-4 Spectrum of neat toluene in a O 015 mm KBr cell 9-5
cell 9-5
cell 9-6
toluene and 3000 methyl ketone in a 0025 mm cell 9-6
toluene and 35 methyl ethyl ketone in a 0025 mm cell 9-6
toluene and 31 methyl ethyl ketone in a 0025 mm cell 9-7
LIST OF ILLUSTRATIONS
Figure
9-10 Spectrum of solution containing 3500 isopropyl alcohol 20 toluene and 45 methyl ethyl ketone in a 0025 mm cell 9-7
9-11 Spectrum of solution containing 50 isopropyl alcohol 14 toluene and 36 methyl ethyl ketone in a 0025 mm cell 9-7
9-12 Plot of volume percent isopropyl alcohol vs absorbance obtained from 817 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-13 Plot of volume percent toluene vs asorbance obtained from 695 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-14 Semilog plot of percent T vs volume percent isopropyl alcohol as obtained from 817 em-1 absorption bands in Figs 9-7 through 9-11 9-9
974
INTRODUCTION
Note The experiments described in this manual are intended to be to aid operators in learning the operation of infrared instrushy
mentation and the basic techniques of sample handling Though they are written for the Perkin-Elmer Model 735 infrared spectrophotoshymeter they may be applied to any infrared instrument by extrapolashytion with the specifications of that specific instrument
Infrared is the portion of the electromagnetic spectrum that extends beyond the visible into the microwave region (Fig 1) It is measured in units of frequency or wavelength In the infrared frequency is usually expressed in wavenumber units or reciprocal centimeters (cm- l) which are the number of waves fer centimeter Wavelength is expressed in microns (10- 3 mm or 10- cm) abbreviated Frequency f and waveshylength A are related by the equation fA bull c where fre~uency is defined as cycles per second and c is the velocity of light 3 x 10 0 cmsec A wavenumber unit v is defined as the reciprocal of wavelength (v bull 104 A) The product of v and c gives the frequency in cyclessec The infrared region extends from approximately 075 JJ to almost 1 mm but the segment most often used by the chemist is from 4000 to 400 cm- l (25 to 25 JJ) termed the fundamental region The low frequency region from 600 cm-1 to 200 cm- l the extended range and the range from 200 cm- l to the microwave region are often called the far infrared The region from 4000 cm-1 to the visible is often called the near infrared or overtone region
All molecules are made up of atoms held together by chemical bonds These atoms vibrate with respect to each other the bonds acting much like springs connecting the atoms Each molecule has its own specific set of vibrational frequencies but different molecules have different sets of vibrations The frequencies of these vibrations are in the same range as the infrared frequencies of electromagnetic radiation
Vfavemunber 10 13 10 10 108 10middot 25105 142 105 4000 650 12 smiddot lO~ 10- 3 10- 6
em-l
lO~7Energy lfiI 1~6 1 102 15 0 7 1O~2 1510- 3 S--lO~6 10- 10
lectron volta
Z5 154 830
Fig 1 - The electromagnetic spectrum
974
ii
Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
974
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
974
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
974
0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
xi
FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
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MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
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Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
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Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
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Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
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Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
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Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
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Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
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Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
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Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
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Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
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4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
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Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
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Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
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Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
LIST OF ILLUSTRATIONS
Figure
9-10 Spectrum of solution containing 3500 isopropyl alcohol 20 toluene and 45 methyl ethyl ketone in a 0025 mm cell 9-7
9-11 Spectrum of solution containing 50 isopropyl alcohol 14 toluene and 36 methyl ethyl ketone in a 0025 mm cell 9-7
9-12 Plot of volume percent isopropyl alcohol vs absorbance obtained from 817 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-13 Plot of volume percent toluene vs asorbance obtained from 695 cm- 1 absorption band in Figs 9-7 through 9-11 9-8
9-14 Semilog plot of percent T vs volume percent isopropyl alcohol as obtained from 817 em-1 absorption bands in Figs 9-7 through 9-11 9-9
974
INTRODUCTION
Note The experiments described in this manual are intended to be to aid operators in learning the operation of infrared instrushy
mentation and the basic techniques of sample handling Though they are written for the Perkin-Elmer Model 735 infrared spectrophotoshymeter they may be applied to any infrared instrument by extrapolashytion with the specifications of that specific instrument
Infrared is the portion of the electromagnetic spectrum that extends beyond the visible into the microwave region (Fig 1) It is measured in units of frequency or wavelength In the infrared frequency is usually expressed in wavenumber units or reciprocal centimeters (cm- l) which are the number of waves fer centimeter Wavelength is expressed in microns (10- 3 mm or 10- cm) abbreviated Frequency f and waveshylength A are related by the equation fA bull c where fre~uency is defined as cycles per second and c is the velocity of light 3 x 10 0 cmsec A wavenumber unit v is defined as the reciprocal of wavelength (v bull 104 A) The product of v and c gives the frequency in cyclessec The infrared region extends from approximately 075 JJ to almost 1 mm but the segment most often used by the chemist is from 4000 to 400 cm- l (25 to 25 JJ) termed the fundamental region The low frequency region from 600 cm-1 to 200 cm- l the extended range and the range from 200 cm- l to the microwave region are often called the far infrared The region from 4000 cm-1 to the visible is often called the near infrared or overtone region
All molecules are made up of atoms held together by chemical bonds These atoms vibrate with respect to each other the bonds acting much like springs connecting the atoms Each molecule has its own specific set of vibrational frequencies but different molecules have different sets of vibrations The frequencies of these vibrations are in the same range as the infrared frequencies of electromagnetic radiation
Vfavemunber 10 13 10 10 108 10middot 25105 142 105 4000 650 12 smiddot lO~ 10- 3 10- 6
em-l
lO~7Energy lfiI 1~6 1 102 15 0 7 1O~2 1510- 3 S--lO~6 10- 10
lectron volta
Z5 154 830
Fig 1 - The electromagnetic spectrum
974
ii
Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
974
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
974
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
974
0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
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It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
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xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
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Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
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Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
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Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
INTRODUCTION
Note The experiments described in this manual are intended to be to aid operators in learning the operation of infrared instrushy
mentation and the basic techniques of sample handling Though they are written for the Perkin-Elmer Model 735 infrared spectrophotoshymeter they may be applied to any infrared instrument by extrapolashytion with the specifications of that specific instrument
Infrared is the portion of the electromagnetic spectrum that extends beyond the visible into the microwave region (Fig 1) It is measured in units of frequency or wavelength In the infrared frequency is usually expressed in wavenumber units or reciprocal centimeters (cm- l) which are the number of waves fer centimeter Wavelength is expressed in microns (10- 3 mm or 10- cm) abbreviated Frequency f and waveshylength A are related by the equation fA bull c where fre~uency is defined as cycles per second and c is the velocity of light 3 x 10 0 cmsec A wavenumber unit v is defined as the reciprocal of wavelength (v bull 104 A) The product of v and c gives the frequency in cyclessec The infrared region extends from approximately 075 JJ to almost 1 mm but the segment most often used by the chemist is from 4000 to 400 cm- l (25 to 25 JJ) termed the fundamental region The low frequency region from 600 cm-1 to 200 cm- l the extended range and the range from 200 cm- l to the microwave region are often called the far infrared The region from 4000 cm-1 to the visible is often called the near infrared or overtone region
All molecules are made up of atoms held together by chemical bonds These atoms vibrate with respect to each other the bonds acting much like springs connecting the atoms Each molecule has its own specific set of vibrational frequencies but different molecules have different sets of vibrations The frequencies of these vibrations are in the same range as the infrared frequencies of electromagnetic radiation
Vfavemunber 10 13 10 10 108 10middot 25105 142 105 4000 650 12 smiddot lO~ 10- 3 10- 6
em-l
lO~7Energy lfiI 1~6 1 102 15 0 7 1O~2 1510- 3 S--lO~6 10- 10
lectron volta
Z5 154 830
Fig 1 - The electromagnetic spectrum
974
ii
Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
974
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
974
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
974
0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
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Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
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Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
ii
Infrared analysis gives the scientist a permanent step- by- step record of his work providing him and his organization with evidence of the dates on which he reached various stages a record which can be invaluable in patent applications In carrying out a complex synthesis he can determine the identity and purity of reagents follow stepwise changes in all materials deshytermine percent yields and can check back at any stage Furthermore there is no fear of having insufficient sample to proceed to the next stage since infrared analysis is nondestructive aiJd the sample is recoverable
Instrumentation
Infrared instruments measure the vibrational spectrum of a sample by passing infrared radiation through it and recording which wavelengths have been absorbed and to what extent Since the amount of energy absorbed is a function of the number of molecules present the infrared instrument provides both qualitative and quantitative information The recorded spectrum is a plot of the transmittance of the sample versus the frequency (or wavelength) of the radiation This spectrum is a fundamental property of the molecule and can be used both to characterize the sample and to determine its concentration
Qualitative Analysis
Since the infrared spectrum of a chemical compound is perhaps its most characteristic physical property infrared finds extensive application in fingerprinting or identifying materials By matching the infrared specshytrum of an unknown with that of a known material proof of identity is estabshylished A library of spectra of the materials most frequently encountered can be accumulated or reference spectra available commercially from varishyous sources can be purchased Identification then becomes a matter of sortshying and matching
The infrared spectrum contains basic information about the composition and structure of a compound Organic compounds for example may contain groups such as -OH -NH2 -CH3 -CO -CN -C-O-C- -COOH -CS etc These groups have characteristic absorption frequencies in the infrared which are usually relatively unaffected by the remainder of the molecule When they are affected by the rest of the molecule additional information about its structure can be obtained An unknown compound therefore can often be characterized by observing the presence of the absorption frequencies associated with such groups Spectra-structure correlation charts like the ones with this manual provide a key to the location of characteristic absorpshytion bands for most of the common functional groups With them the investishygator can quickly determine the gross structural features of an unknown by band identification and reduce the number of possibilities so that matching the unknown to a library of reference spectra can be done in a matter of minutes If however the investigator does not have access to a reference
974
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
974
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
974
0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
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FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
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Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
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Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
spectrum for the compound under investigation he can often identify it by functional group analysis together with a few easily determined physical and chemical properties See the interpretation section for examples of this
A great advantage of infrared to the scientist is that the spectrum is interpreted in terms of the same concepts he uses in studying chemical propshyerties bonds and bond groupings Characteristic absorption bands in the specshytrum provide information regarding the chemical nature of the sample The investigator can apply his knowledge of chemical bonding to his interpretation of the spectrum He can quickly use infrared without having to learn an enshytirely new language
Quantitative Analysis
Another important use of infrared is in the quantitative analysis of chemical mixtures Since the depth of an absorption band is proportional to the concentration of the component causing that band the amount of a comshypound present in a sample can be determined by comparing the depth of that band with its depth in a spectrum from a sample containing a known concentrashytion f the material Usually the spectra of a few samples with known conshycentrations of the compound are obtained to provide a working curve of absorbshyance vs concentration from which the concentration of the unknown may be easily determined The spectrum of a mixture is usually a superposition of the spectra of the pure components Absorption wavelengths unique to each component are chosen and the sample transmittance at the chosen wavelengths is measured and related to the component concentrations
Variation of Spectra with Structure and Composition
If infrared radiation of a given frequency strikes a sample whose molecules have a vibrational frequency the same as that of the incident radiashytion the molecule absorbs radiant energy and the energy of the molecule is increased If the incident frequency differs from the characteristic frequenshycies of the molecule the radiation passes through undiminished The charshyacteristic frequencies for a particular molecule are determined primarily by the masses of the atoms in the molecule and the strength of the bonds connectshying them Furthermore the proximity and spatial geometry of various groups may often influence their vibrations
If a pair or group of atoms is to absorb infrared radiation it must undergo a change in dipole (dipole moment) during the vibration The changing dipole couples the vibration of the molecule with that of the radiation much as air (or any other fluid) between two fans couples the motion of one fan with the other If an unconnected fan is placed opposite a moving fan in a vacuum the unconnected fan will not move If air is admitted to the system it couples the motion of the moving fan to that of the unconnected fan which ideally rotates at the same frequency as the fan to which power is supplied
974
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
974
0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
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It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
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xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
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Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
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Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
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Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
iv
H H H Cl
C C
H
H
H H
C c
The two carbon atoms have Presence of chlorine alters charge same charge stretching vishy distribution so that the carbon atoms brations produce no change have a small but significant difference in dipole moment in charge density Carbon stretching
vibrations cause a change in dipole
Fig 2 - Stretching of carbon-to-carbon double bonds in ethylene and chloroethylene
The stretching of the carbon- carbon double bond in ethylene (Fig 2) does not absorb infrared radiation because there is no change in dipole during the vibration This inactivity of a vibrational frequency often occurs when the vibrating group lies at or neara center of symmetry within the molecule The stretching of the carbon-carbon double bond in chloroethylene causes a signifishycant change in dipole moment and this double bond has a strong infrared abshysorption The changing dipole couples the electromagnetic radiation with the vibrating carbon atoms
Molecular vibrations can be classified as stretching or bending vibrashytions (Fig 3) The latter are sometimes called deformation and are subshyclassified into scissoring wagging twisting and rocking The frequencies of the stretching and the bending vibrations like the frequencies of all
~ Bending or Deformation
Stretching
o 0 o 0 0 0 0+ 0 0+ +0 0 ~- ~~ XXX(
T i T
i i Aayrmnetric Synunetric Scissoring Twisting Wagging Rocking Stretching Stretching
Fig 3 - Types of vibrations
974
0
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
xi
FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
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Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
mechanical oscillators are dependent upon the masses of the vibrating units (atoms or groups of atoms) and the stiffness of the spring-like conshynections (chemical bonds) joining the vibrating units Stretching vibrations always have a higher than the bending vibrations of the same group The lower the masses of the atoms the higher the frequency of vibration The stiffer the bond the higher the frequency of vibration A bonds stiffness or its force constant is roughly proportional to bond strength which in turn is roughly proportional to the bond order That is for groups with atoms of the same mass a triple-bonded group has a higher vibrational frequency than a double- bonded group and the double- bonded group has a higher vibrational frequency than a single- bonded group A group bonded with a single bond that has partial double- bond characteristics such as often results from resonance has a vibrational frequency intermediate between those of the same group with pure double and single bonds
Vibrations of groups where one atomic nucleus is a proton have the highest frequencies of all molecular vibrations All stretching vibrations of hydrogen atoms occur abqye 2250 cm- l bull No other groups have fundamental absorptions in this regi~n although overtones from lower frequency vibrations are sometimes observed above 2400 cm- l Groups with triple bonds absorb in the next highest region of the spectrum from 2300 to 2100 cm- l bull The only other principalgroup to have fundamental absorptions in this region are those with cumulated double bonds (2350 - 1930 cm- I ) as -C=C=O Cumulated double bonds absorb at a higher frequency than other double bonds (1900 - 1580 cm- l ) because of coupling between th~ cumulated bonds
Coupling or mechanical interaction occurs when two groups having similar frequencies are close to each other in the same molecule In effect resonance is established between the two vibrating groups and vibrational energy flows back and forth between them so that the vibrations of the two groups modify each other Another way of viewing this is that the coupling groups lose their individual vibrations and vibrate together Coupling is strongest when the two interacting groups share a common atom and the freshy
of the two groups are very close or identical
Carbon dioxide is such a molecule The stretching frequencies of most carbonyl groups is somewhere near 1700 cm-1 In carbon dioxide the two carbonyl groups vibrate together with the asymmetrical vibration occurshying at 2350 cm- 1 and the symmetrical vibration occurring at approximately 1330 cm- l bull The symmetrical vibration is actually a complex widely spaced doublet because of Fermi resonance with an overtone from a bending vibrashytion The symmetrical vibration does not cause an infrared absorption beshycause no change in dipole occurs The regions for the various vibrations are summarized in Figure 4
974
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
xi
FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
vi
FREQUENCY ICM )
2800 2400 2000 1800 1600 1400 1200 1000 800 650
Fig 4 - Absorption in different regions of the spectrum For use in identification of various groups in spectra of unknowns this chart is included full size at the back of this manual as Appendix 1
Interpretation of Infrared Spectra
There is no high intellectual barrier to interpretation of infrared spectra For facile good interpretation one needs a thorough understanding of the principles outlined above an infrared cor relation chart a reasonable knowledge of structural organic chemistry (and inorganic chemistry if inorshyganic compounds are to be examined) and experience The first two are proshyvided with this manual The third can be obtained by a formal introductory course in organic chemistry such as almost all scientists study as part of their undergraduate curiculum
There is of course no short cut to experience The problems that follow are intended to give users of Perkin-Elmer spectrophotometers a beginning More experience can be obtained from the references listed after the problems from the short infrared interpretation courses offered at various universities and from the interpretation of spectra obtained from the spectrophotometer in its day-to-day application
The first step in the interpretation of an infrared spectrum is to look at the entire spectrum keeping in mind any other information about the comshypound that might aid in its identification such as source state boiling point etc The general appearance of the spectrum usually gives clues to the identity of the compound The following specific regions should then be examined
974
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
xi
FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
vii
Look first at the 3800-2250 cm- 1 ranfe for hydrogen stretching abshysorptions A set of bands at 3000-2800 cm- indicates hydrogen on saturated carbon atoms at 3100- 3000 cm- 1 hydrogen on aromatic vinyl or cycloshypropyl carbon atoms A very sharp band at 3300 cm- l indicates the hydrogen on a terminal acetylene unit (-CliCH) Other sharp bands above 3100 cm- l
are due to unassociated hydroxyl or amino groups Very broad or ill defined bands between 3300 and 2250 cm- l are from associated -OH and NH groups Broad absorptions between 3000 and 2250 cm- 1 are either from OH of acids or N-H of amine salts A doublet at 2820 and 2720 cm- 1 is from the proton on the carbonyl carbon atoms of aldehydes and is very characteristic of these compounds As indicated above absorptions from 2275 cm- l to 1930 cm- 1
are from triple or cumulated double bonds Since not much else absorbs in this region bands here are very diagnostic
The double-bond region from 1900 cm- 1 to 1500 cm- 1 should be exshyamined next Strong bands between 1900 and 1660 cm- 1 a1most always indishycate carbonyl groups although some carbonyl groups such as those with exshytensive conjugation andor strong hydrogen bonding some amides and carboxylate salts absorb at lower frequencies See Table V in the accompanyshying frequency correlation booklet for absorption of specific groups The double- bond region also includes bonds from ethylenic type linkages (very weak to moderately strong 1685-1630 cm-1) aromatic structures (several from 1620-1450 cm- l ) aromatic heterocyclics (several from 1660-1490 cm- 1) conjugated dienes and trienes (one to three bands from 1650 to 1600 cm- l ) and polyenes (broad band at 1650-1580 cm- l ) The presence of these unsaturated systems can be verified and specific structural types determined by
1 the exact frequency of the band
2 the moderate to strong out-of-plane bending vibrations between 1000 and 660 cm- l (Tables III and IV in the accompanying frequency correlation booklet) and
3 the weak overtone combination bands between ZOOO and 1650 cm- l (Table I in the frequency correlation booklet for aromatics and 1860-1800 cm- l for -CHCHZ and 1800-1750 cm- l for CCHZ)
The next region to examine is lZ50-1000 cm- 1bull Very strong bands here with no other very strong bands from 1580-940 cm- l are indicative of C-O stretch such as is found in ethers esters carboxylic acids and their anhydrides alcohols and phenols
Bands in the 1390 to 1350 cm- l region are indicative of methyl groups A doublet here indicates a gem dimethyl or trimethyl groupbull Very intense bands between the carbonyl region and 940 cm- l are usually due to polar
974
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
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Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
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Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
viii
I groups containing oxygen or fluorine such as -P=O -P-O- -N=O -N-O- -8=0 -8-0- C-O- etc Some of these bands such as those from -NO -NOZ and S03H are the most intense of all infrared absorption bands as might be expected from the large changes in dipole caused by vibrations of
lthese groups Strong bands below 810 cm- are often from carbon-chlorine stretch vibrations Carbon-bromine and carbon-iodine stretch vibrations
l are usually below 620 cm-
Other absorption bands in the spectrum are useful for verifying the general structural features indicated by the above procedure for obtaining information on other structural features and for fingerprinting the comshypound
The spectra for the following examples were obtained on the Model 735 and should be essentially identical with spectra you would obtain froITl the same sample on your instrument It is suggested that you first look at the spectra and the information about the compounds given in the captions With thes e data try to identify the compounds Then read only the first parashygraph of the interpretation 1pound the interpretation there is different than the one you obtained reevaluate the data and attempt to identify the compound again Then read the rest of the interpretation 1pound you missed try to deshytermine where your interpretation went astray By following this procedure even if you miss every problem you will take a big step in beginning to obshytain the experience that is needed to interpret infrared spectra
Example 1 A liquid compound has a formula C5HIZ0 and gives the absorpshytion spectrum shown in Figure 5 A quick glance at the spectrum shows that the strongest bands are at 3300 cm- 1 (broad) 2940-2860 cm- l and 1060 cm- l (sharp) The broad 3300 CIn- l band indicates associated OH and the band at 1060 cm- l is probably froIn carbon-oxygen stretching The 2940- 2860 CIn- l absorption is clearly froIn hydrogen on a saturated carbon atOIn There is no absorption from olefinic or aroInatic hydrogen and there are no other absorption bands which could be froIn unsaturated groupings The infrared spectrum shows that the COInpound is definitely an alkanol This is verified by the molecular formula whi ch is consistent only with an alkanol or saturated ether
The C-O stretch at 1060 CIn- l can be from a primary alcohol with no branching at the second carbon -CH2CHZOH (1050 CITl- l ) or a secondary alcohol with double branching at one carbon atOIn adjacent to the -CHOH group
1 laquoH
-C-laquo-laquo-CHZshyC OH
1
974
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
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FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
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xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
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Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
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Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
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Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
FREQUENCY (CM) 000 3600 3200 2800 2400 1800 1600 1400 1200 1000 BOO 601)
Fig 5 Infrared absorption spectrum of C5HIZ0 in a 0025 mm cell
The latter structure is inconsistent with the formula and with the spectrum in the 1400-1100 cm- l region With -CHZCHZOH known three more carbon atoms must be accounted for The doublet around 1380 cm- 1 indicates a gem dimethyl group The fact that the intensity of the lower frequency band is not considerably stronger than that of the higher frequency band indicates that the doublet is not from a tertiary butyl group This alone however does not comyletely rule out the tertiary butyl group Absorptions at 1175 and 1130 cm- indicate an isopropyl group although many absorptions occur in this region which may either mask or be mistaken for the two bands that verify an isopropyl group In any event the only group that is consistent with this and the other information on the molecule is isopropyl (CH3)ZCH- This and the -CHZCHZOH group indicate that the compound is isoamyl alcohol or 3-methyl-l- butanol (CH3)ZCHCHZCHZOH
Example 2 - A liquid compound of molecular weight 84 + 3 gives the spectrumlshown in Fig 6 The strong aliphatic C-H stretching near 2950 cm- the
ldeformation absorptions at 1365 and 1465 cm- and the lack of any absorptions that could possibly be from functional groups show that the compound is an alkane An alkane of the molecular weight indicated would have six carbon atoms and possible molecular formulas of C6H14 for a noncyclic compound C6H12 for a monocyclic compound and C6HlO for a bicyclic compound
The incompletely resolved multiplet around 1370 cm-1 indicates a gem dimethyl group with possibly another type of methyl group The much stronger low frequency absorption of this multiplet indicates a tertiary butyl group The tertiary butyl group is verified by the absorptions at 1255 and 1215 cm-1 and by the weak absorption at 930 em-I With (CHS)3C- established
974
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
xi
FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
It
FREQUENCY (CMi 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6 - Infrared absorption spectrum of a liquid with a molecular weight of 84 3 run in a 0025 rnrn cell
two carbon atoms remain These can only be arranged as an ethyl group This is verified by the absorption at 780 cm-lwhich is probably from methyshylene rocking These occur at 790-770 cm- 1 for ethyl 745-732 cm- 1 for ~-propyl and 725-715 cm- l for four or more methylene groups in series This absorption not only shifts to lower frequencies with an increasing numshyber of methylene groups but also increases in intensity In unsaturated and polar compounds the absorption is often not observed because it is so weak relative to other absorptions or because it is masked by strong bands beshytween 800 and 700 cm- l bull The compound is 2 Z-dimethylbutane or neohexane (CH3hCCHZCH3
Example 3 - A liquid (C8H70CI) in a 0025 mm cell gives the infrared abshysorption spectrum shown in Figure 7 Absorptions between 3100 and 2900 cm- l indicate hydrogen on both saturated and unsaturated carbon atOITls
lThe strong absorption at 1685 cm- can only be from a carbonyl group The absorptions at 1585 cm- l with shoulders on either side and at 1485 cm- 1 inshydicate an aromatic ring
The formula and carbonyl absorption allow only an aldehyde ketone or acyl chloride The absence of a doublet at Z870 and 2720 cm- 1 argues against an aldehyde and acyl halides have carbonyl stretch absorption freshyquencies above 1740 cm- l bull Only a ketone remains and the 1685 CITl- 1 locashytion indicates a ketone conjugated with an aromatic ring This is verified by the strong band at 1260 em-I The location and intensity of this band vary enough however to make it not too reliable for verifying the presence of ketone groups It is doubtful that the halogen is alpha to the ketone group as this usually shifts the carbonyl stretch absorption to a higher frequency
974
xi
FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
xi
FREQUENCY (CM1 000 3600 3200 2800 2400 2000 1800 1600 100 1200 1000 800 600 400
Fig 7 - Infrared absorption spectruIn of C8H70Cl in a 0025 InIn cell
by 10 to 25 CIn- l The bands at 1430 and 1355 CIn- 1 are consistent with a Inethyl group alpha to a carbonyl FroIn the above inforInation we know the
9 COInpound Inust be an aryl Inethyl ketone ArCCH3 Consideration of the forInula and lack of evidence for other functional groups gives a structure of
CIS]
with only the position of the chlorine atOIn left undecided The strongest absorption in the out-of-plane bending region is at 833 CIn- l This indicates 14- or 135- substitution The Inolecular forInula and lack of another strong absorption band between 730 and 675 CIn- 1 rule out the latter possibil shyity The two weak absorptions (1910 and 1780 CIn- 1) in the unsaturated overshytone-coInbination region verify para substitution The COInpound is P- chloroacetophenone
974
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
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Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
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Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
xii
REFERENCES
MONOGRAPH
Bauman R P
John Wiley and Sons London 1962 pp 593
Barrow G M The Structure of Molecules W A Benjamin New York 1963 pp 153
Co1thup N B Daly L H and Wiber1ey S E Introduction to Infrared and Raman Spectroscopy Academic Press New York 1964 pp 484
Kendall D N Applied Infrared Spectroscopy Reinhold Publishing Corporation Chapman and Hall London 1966 pp 532
Potts W J Chemical Infrared Spectroscopy John Wiley and Sons New York 1963 pp 312
Interpretation Only
Cairns T et al Spectroscopic Problems in Organic Chemistry Heyden and Son Ltd London 1964 Volume I - 60 problems 1966 Volume IV - 60 problems
DESCRIPTION
Mainly theoretical considerations some instrument accessory and experimental information a little interpretation Some ultraviolet discussions
Simplified theoretical About 40 infrashyred Rotational and electronic spectra also
Most comprehensive text in this list on theory and interpretation of vibrational spectra
Very comprehensive Includes special topics Better suited for thos e with some infrared experience
Experimental techniques spectrometer optics and operation basic theory quantitative analysis
Answers to problems available from publisher NMR ultraviolet and infrashyredand in Volume n mass spectroscopy
974
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
xiii
MONOGRAPH DESCRIPTION
Dyer John R About 3000 infrared NMR and ultraviolet Applications of Absorption spectra Spectroscopy of Organic Compounds Prentice-Hall Inc Englewood Cliffs N J 1965 pp 132
Nakanishi K Text tables and problems with answers Infrared Absorption Spectroscopy All infrared Holden Day San Francisco California 1962 pp 220
Swinehart J S Tables prograIllIlled text and problems Introduction to Interpretation with answers 7500 infrared of Spectra Wadsworth Publishing (in press Jan 1975)
Bellamy L J Reference text Infrared Spectra of Complex Molecules Methuen amp Co LTD London England (1954) pp 425
974
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 1-1
EXPERIMENT 1
Instrument Operation and Calibration
OBJECTIVE
To become acquainted with the operation of the Model 735 and with calibration of the wavenumber scale
MATERIALS
The Model 735 instruction manual and a polystyrene film
INTRODUCTION
The Model 735 is quite simple to operate and will quickly produce quality spectra There is however one set of spectra which should be obshytained at least once a week and more often if the instrument receives heavy use These spectra should be dated and kept since they provide a continuous record of instrument performance Variations in these spectra can be used as guides for modifying analytical procedures or to detect incipient troubles Comparison of the most recent spectra with those obtained when the instrushyment was new will allow quick detection of deterioration in instrument pershyformance that would probably go unnoticed for a considerable time without such comparison
PROCEDURE
Part I Operation of the Instrument Performance Checks
Turn the instrument on and place a sheet of paper on the recorder as described in the instrument instruction manual Carefully align the chart paper with the index mark on the recorder scale The gain and balance should be set according to the instructions in the manual
Set the SCAN switch so it is not lit or flashing and move the recorder to the right until the arrow points to 4000 em-I Without a sample in either the sample or reference beam adjust the 10000 control until the pen reads 95 on the transmission scale Start the scan by pressing the SCAN switch and record the 10 or baseline as shown in Figure 1-1 It should be flat within the specification noted in the manual
At the completion of the scan the SCAN switch will flash Depress the SCAN switch return the recorder to 4000 cm- l and adjust the 100 conshytrol until the pen reads 100
974
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 1-2
FREQUENCY (CM) 000 3000 3200 2800 2~00 2000 1800 1600 1400 1200 1000 800 AOO
Fig 1-1 - 10 baseline
Adjustment of the 10000 control for a 10000 transmission reading with no saITlple in the spectrophotoITleter has been found to be the most generally useful setting for running spectra of saITlples particularly unknown samples This setting will prevent the pen from running off the chart above 10000 with possible loss of spectral inforITlation If an occasional saITlple has low transshyITlission overall a second spectrUITl with the 10000 control adjusted for maxishyITlum utilization of the transITlission scale =ay be obtained Even this ITlay not always be necessary for a good spectrum is by definition one which yields the desired inforITlation
Part II Obtaining a SpectrUITl of the Polystyrene Calibration Sample
With the 10000 control adjusted for a 10000 transInlssion reading place the polystyrene calibration saITlple in the saITlple holder of the instrument and scan the spectrUITl of polystyrene on the saITle piece of chart paper used for the 10 scan froIn 4000 to 400 CIn-l ReITlove the chart paper from the recorder as described in the instruction Inanual and fill in the appropriate inforInation on the upper part of the chart
The spectruITl of polystyrene contains a convenient set of absorption bands which =ay be used to verify the calibration of the frequency scale of the instrument These peaks are nu=bered in Figure 1- 2 and their positions should be cOITlpared with the frequencies tabulated below The experiITlentally deterITlined frequencies should agree with the tabulated values to within plusmn 8 cm- l
from 4000 to 2000 CITl- I and withinplusmn4cm- 1 from 2000 to 400 em-I
974
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 1- 3
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 ISoo 1600 1 00 1200 1000 800 600
Fig 1- 2 - Polystyrene calibration sample spectrum (005 mm film)
PEAK FREQUENCY cm- l WAVELENGTH p
1 3027 330 2 2851 351 3 1944 514 4 1802 555 5 1601 625 6 1495 669 7 1181 847 8 1154 867 9 1028 973
10 907 11 02 11 699 1431
974
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
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Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
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Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 2-1
EXPERIMENT 2
Care and Handling of NaCl and KBr Crystal Windows
OBJECTIVE
To become acquainted with procedures for cleaning polishing and cleaving optical grade NaCl and KBr windows to be used in infrared analysis
MATERIALS
For Cleaning Solvent for the sample material which will not affect the crystal
For Polishing Finger cots or rubber gloves and Perkin-Elmer Crystal Polishing Kit (186-0429)
For Cleaving Razor blade and small hammer
INTRODUCTION
The care and handling of the crystal windows used in demountable cells and demountable sealed cells is critical to the quality of any infrared analysis Window fogging caused mainly by etching of the window surfaces by water vapor may result in a sloping baseline or in excessive reduction of the energy transmitted by the cell Sample residues occluded on window surfaces may absorb energy in a way which will seriously hinder the interpretashytion of other spectra or reduce the accuracy of quantitative analyses These difficulties can be overcome by keeping the windows clean and dry and by polishing them when necessary using the procedures described
Furthermore windows that are cracked or broken may still be useable Large pieces may be found suitable for running samples harmful to the crystal material where it is not desirable to ruin a good window Smaller pieces can be cleaved as described and used in microsampling cells
Table I lists properties of crystal materials which are important as aids to maintaining and handling cell windows
974
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
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Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
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Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
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Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 2-2
Table I
Crystal
Properties
Useful Range (cm-l)
of Crystal Materials
Water Solubility g100 cc H2O) Other Properties
NaCl 10000-650 357 Cleaves and polishes easily
KBr 10000-400 538 Cleaves and polishes easily
CaF2 10000-lllO 00017 Does not cleave difshyficult to polish
BaF2 10000-760 017 Obtained as sawed blanks moderately easy to polish
Irtran-2 10000-715 Insoluble Glasslike withstands severe thermal shock Difficult to polish
PROCEDURE
Part I - Cleaning the Windows
Sodium chloride and potassium bromide crystal windows can be cleaned easily by washing with a solvent (not water) for the film or sample on the window However if the sample is insoluble or if the crystal surface has become fogged or scratched it may be necessary to polish the crystal as described below If the window is merely fogged omit grinding on the sandshypaper and proceed to the polishing operation
Part II - Grinding Cell Windows
When the polishing kit is being used follow the directions below
The grinding operation is carried out on one of the ground glass plates A small amount of abrasive is poured on the-plate and enough ethyl alcohol is added to make a slurry
To grind the surface of a crystal use strokes 3 to 4 inches long preferably in a figure eight pattern After 10 to 15 strokes rotate the crystal 90 and use an additional 10 to 15 strokes to obtain even wear The plate should not be allowed to dry A very small amount of grinding comshypound will polish several crystals
Use no 400 abrasive for rough grinding and no 600 for fine grinding Wash the glass plates before changing abrasives Scratches can occur from unclean abrasive
974
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 2-3
Part III - Polishing Cell Windows
Put the self-adhering polishing pad on one of the ground glass plates Mix a slurry of Barnsite and water and brush onto the back third of the pad (Other polishing compounds are available such as Linde metallographic polishing compound) Rub the crystal in a brisk manner gradually working toward the dry portion of the pad About 25 strokes should be enough to polish the surface and 10 or so strokes to buff on the dry portion of the pad Fig 2-1 - Correct way to polish crystalWipe the edges of the crystal with a materials for infrared sample cells dry rag
Inspect the window surface to see whether additional polishing is required The surface should be clear and free from scratches A small amount of orange peel may be evident tpis is acceptable if barely noticeable If no further polishing is needed grind and polish the other side of the window
Mter both sides of the window have been polished obtain a spectrum of the window to detect any residual polishing compound which might remain on the window The spectrum of a clean NaCl window is shown in Fig 2-2a and the spectrum of a clean KBr window is shown in Fig 2-2b If the spectrum
FREQUENCY (CM) lt1000 3600 3200 2800 2400 2000 1800 1600 IAoo 1200 1000 800 600
Fig 2-2a - Spectrum of clean sodium chloride window 4 mm thick
974
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 2-4
FREQUENCY (CM ) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 2-2b - Spectrum of clean potassium bromide window 4 mm thick
appears to indicate the presence of polishing compound as shown in Fig 2-3 wipe the window carefully on a clean portion of the polishing cloth moistened with alcohol Wipe carefully on a clean dry portion of the cloth Rerun a spectrum of the window
Part III - Cleaving NaCl or KBr Plates
NaCl (or KBr) plates may be cleaved to form smaller rectangular windows satisfactory for many qualitative and semi-micro applications It is preferable to prepare the smaller windows from cracked or broken plates produced as a result of thermal shock or accidental dropping
FREQUENCY (CM) 000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 800 600 400
gH+H+M+H LmiddotmiddotmiddotImiddotmiddotmiddot ~t+ttlrtttirttH+1
Fig 2-3 - Spectrum of 4 mm thick sodium chloride window with residual
polishing compound
974
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 2-5
Fig 2-4 - Cleaving a sodium chloride crystal
)
I
e i ~
~ j - shyI
I
Fig 2-5 - Cleavage planes of a crystal window
The actual process of cleaving NaCl or KBr is quite simple but requires a little practice Place the crystal to be cleaved on a flat clean firm surface Hold a single-edge razor blade parallel to one of the flat sides of the piece to be cleaved at about the center and tilted slightly so that the blade contacts the crystal at an edge as shown in 2-4 Tap the back of the razor blade sharply with a small hammer and the crystal will cleave into two pieces A little experience will soon indicate how hard to strike the razor The two pieces may be cleaved again along anyone of the three perpendicular cleavage planes shown in Fig 2-5 to obtain still smaller pieces Each time it it cleaved the crystal should be divided into roughly equal pieces The cleaved sections produced can often be used without further polishing for many qualitative applicashytions If polishing is necessary or desirable then Part II described above should be followed
Note Only single crystal NaCl or KBr plates can be cleaved Saw blanks which are often used in sealed and demountable cells will not cleave
974
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 3-1
EXPERIMENT 3
Determining the Thickness of a Sealed Cell and of a Polymer Film
To determine the thickness of a sealed liquid cell and of a polymer film by the interference fringe technique
A sealed cell (thickness 0015 to 03 rom) and the polystyrene calibrashytion film
INTRODUCTION
The thickness of sealed cells is one of the basic measurements required for quantitative The value should be verified from time to time since the thickness may change due to a gradual erosion of the internal surshyfaces of the crystal windows in the celL In addition to the thickness of cells the thickness of polymer films is also important both for quantitative analysis of the film and for a knowledge of the thickness itself
The basis for the measurement is the interference fringe pattern proshyduced when the transmission of the film or empty cell is recorded over a range of frequencies This pattern an effect of the wave nature of light reshysults from the interaction between radiation which is reflected by the inner surfaces and then transmitted Unless absorption occurs most of the radiashytion at any given wavelength is transmitted A small amount however is reflected and then transmitted as shown in Figure 3-1 a simplified schematic diagram The amount reflected depends on the difference in the refractive indexes of the two materials at the reflecting interface
The reflected radiation as finally transmitted may be exactly in phase with the radiation not reflected it may be exactly out of phase or it may be somewhere in between If in phase reinforcement occurs and the cell (or film) transmission is maximum if out of phase destructive intershyference occurs and the transmission is minimutn Between the maxima and minima the transmission changes gradually with frequency as radiation which is neither entirely in phase nor entirely out of phase interacts As the spectrophotometer scans the cell or film transmission at one wavelength after another a wavy interference fringe pattern emerges such as that shown in Figure 3-3 or Figure 3-4
974
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
c
Page 3-2
A B
- =-~~~ ---- -- --- --shyo
~---------d--------~v
-------REFLECTED -------REFLECTED
----- TRANSMITTED ---- TRANSM ITTED
Fig 3-1 - Path of radiation between Fig 3-2 - Wave patterns for transshythe inner surfaces of a filITl or cell ITlitted and reflected portions of radiashyPath of reflected radiation is drawn tion when cell thickness d is such at an angle to separate it froITl that that 2d ITlll the in-phase condition transITlitted for a fringe ITlaxilnuITl The reflected
radiation as finally transITlitted is in phase with that transITlitted directly
The thickness d of a ce1l or filITl can be calculated from data obtained froITl the fringe Jlattern by using Equations land 2 below
AmFor cells d = Equation 12(vl-v2)
AmFor filITls d = Equation 22n(vl-v2)
where d= thickness in centimeters (em)
frequency at which first ITlaxiITlurn (or ITlinimum) occurs in wavenumber (em-I) units
v2 = frequency at which last maxhnurn (or minimum) occurs in wavenumber units
cm number of complete fringe maxima (or minima) in the interval from VI to v2 a whole number One complete fringe minimum is from point X to point Y in Fig 3-3
n = index of refraction for the filITl
The use of these equations should become apparent when performing the Proshycedure which follows These equations and their origin are discussed in more detail in the Discussion following the Procedure
974
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 3- 3
PROCEDURE
Part I - Thicknes s of a Sealed Cell
Place an eITlpty sealed cell (noITlinal thickness 0015 to 03 ITlm) in good condition in the saITlple beam and obtain the spectrUIll from 4000 to 400 CITl- l The spectrum produced should be slITlilar to that shown in Figure 3- 3 except for the spacing between ITliniITla or ITlaxima The calculation based on Equation 1 is deITlonstrated on the figure with appropriate values of Am VI and vZ Note that as many fringes as possible are counted in order to reshyduce the effect of errors in ITleasuring vl and vZ
Part II - Thickness of a Polymer Film
Place the polystyrene calibration film in the sample beam of the inshystrUIllent Obtain a spectrUIll from 4000 to 400 ern-I The curve should be similar to that shown in Figure 3-4 The interference fringes used in the calculation are noted on the curve In this case Equation Z should be used A refractive index value of 1 6 was used for polystyrene The operator should be ahlp to verify that his polystyrene film is approximately the same thickness as deterITlined in the exaITlple
DISCUSSION
The phase relation beheen radiation translTIitted straight through a cell (or film) and that reflected by the inner surfaces and then transITlitted depends on several factors In the case of the Model 735 where the rays of incident radiation are perpendicular on the average to the cell (or film) surshyfaces the phase relation depends on the cell or fillTI thickness d the radiation
FREQUEtoICY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 3-3 Fringe pattern obtained for an elTIpty O 1= thick sealed KBr cell
974
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 3-4
FREQUENCY (CM) ~ooo 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 00
I
I 11
_LJ-j-H-+-t+t-H-++--++++~+t+++-tt-~t+ilm i r-t-HffI+IH+H-H+f-IttI+f1-t-H-H+HH-+HI ~~-H-tIHH+++I HH+ ~ i ji I i-I 6m=ll 6m - - r~ ~ 1~1r-H-j ~ ++ d = 2n(v1-v2)tlt+ttti++-ttttti++-t+-Irtt-rttf vl
j Ii j-shy
II i
t laquot-Z I f~ 27~cxm~lf I 11 I I III _-----11------_ 1
1-++++i+++++++i++H+-IIH-HI--++++++l-4+++V2 = -l+m-tH1+1+m-t-l-i---H-H d = 2 x 16(2700 - 2025)-H-t4+i-IH++h4-l ~ I I I I i I 2025cm- 1 f t ZI-++tti++-ttttti-l+t+tIrll-IHH+t+l--l+++t+l-t+t-H-H+-+++-H-t+l+C14yen1-t-m-ttit+l+H d = 0005 Oem -H-m-tH+H+-t-t ~ 1 I I 1 + W- ti -ttH+rr+rrm1 d = 005 Cbm i i
1-++++i++H-f-~+f+++~-Jfl~H+H+l-rt+++i-H~~-tHH+-H++lH+I++H-H~j+H-H-t-H-tH-f-j-H-tHI-H-jjll 20 i1 II HW+I+HH
r-t+H+H+Ht~tlJr-t+r-tt-H + o
25 35 (MICRONS) 11 1213 I 16 l 20 25
Fig 3-4 - Fringe pattern obtained with the 005 nun thick polystyshyrene calibration saITlple
wavelength A and in the case of a filITl the index of refraction n If the phase relationship and wavelength are known therefore it is possible to deshyterITline the thicknes s of an eITlpty cell If in addition the index of refraction for a filITl is known then its thickness can also be found Except for the inshydex of refraction all of this infoxITlation is available in the fringe pattern of the cell or filITl transITlission On the other hand if the filITl thickness is known froITl SOITle other ITleasureITlent the refractive index ITlay be deterITlined
Figure 3-2 is a ITlodification of Figure 3-1 showing the relation between cell thickness and phase in a siITlplified fashion Here the cell thickness d is =ade equal to one wavelength or d = The reflected wave travels a disshytance 2d farther than the wave not reflected If the distance 2d is equal to ITlA (where ITl is any whole nUITlber) the reflected and nonreflected waves will eITlerge froITl the cell cavity in phase and the fringe pattern will show a ITlaxiITlUITl a ITliniITlUITl will occur when 2d = (ITl + 12)1 We now have a ITlatheITlatical relashytionship between cell thickness and wavelength which is related directly to the fringe pattern For any ITlaxiITluITl the cell thicknes s is
d = rnA Equation 32
However the fringe pattern does not give a value for ITl directly It does show the wavelengths at which various ITlaxiITla occur Since the value of ITl changes by 1 for adjacent ITlaxiITla (or ITliniITla) the following relations can be established for two different ITlaxiITla in the fringe pattern
974
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
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Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
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Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 3-5
m1 Al 2d (for maximum 1)
m22 2d (for maximum 2)
ml-m2 = 2d -1
-2d A2
Solving for d
12 (m 1-m2 ) d =
2(rAl)
Am then
A1 A2 (~m) d = Equation 4
2([2-1-1)
Note that in Equation 4 the quantity (A m) corresponds to the number of maxima between wavelengths 1 and 2 For an empty cell the value of d depends only on the wavelengths at which the two chosen maxima occur and the nUluber of maxima between them
When the thickness of a film must be measured the nmnber of waves in the film depends on the index of refraction n This value must be obtained from a handbook or other source Equation 3 now becomes
d = rnA 2n
and Equation 4 becomes
Equation 5
Generally Equations 4 and 5 will enable the user of the Model 735 to determine the thickness of a cell or film Both equations however are based on the premise that the incident radiation is propagated in a direction perpendishycular to the film or cell surfaces (angle of incidence = 0 0 ) which is the normal situation in the Model 735 If the angle of incidence 1) were not 0 0 it would be necessary to use the general equation for thickness which is
d Equation 6
This reduces to Equation 5 when () 0deg
974
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
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Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 3- 6
Throughout the discussion above the calculation of cell or film thickshyness is based on a unit of wavelength (in the infrared the micron) It is more convenient to make the calculation using wavenumber units when using the spectroshyphotometer For any given wavelength the corresponding wavenumber is the number of waves which will occur in one centimeter If wavelength II is given in microns the usual unit for infrared radiation then the corresponding wavenumber is 104 11 waves per centimeter (cm- l )
Wben wavenumber units are used Equations 1 through 6 must be modishyfied Equation 3 for cell thickness based on n = 1 at a fringe maximum becomes
4d == 10 m where d is in microns Equation 72v
1pound d is in centimeters then
d = 2v
Equation 1 for cell thickness based on n 1 becomes
Equation 2 for film thickness based on n 1 becomes
Equation 9
Equation 6 for film thickness based on n I 1 and an angle of incidence () 0 becomes
Equation 10
974
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 4-1
EXPERIMENT 4
Spectra- of Pure Liquids
OBJECTIVE
To obtain the infrared spectra of several pure liquids and to demonstrate the procedures used
MATERIALS
Indene carbon tetrachloride carbon disulfide mineral oil (such as Nujol) perfluorohydrocarbon oil (such as Fluorolube) silicone grease demountable cell O 1 mm sealed cell or demountable sealed cell two NaCl or KBr windows for demountable cell spacers for demountable cell eye droppers 1 ml glass syringe rubber ear syringe
INTRODUCTION
Perhaps the simplest most common method of sample preparation for the infrared examination of liquids involves placing an undiluted sample between a pair of transparent crystal windows This sandwich is clamped together and placed in the sample holder of the spectrophotometer and then the spectrum is obtained This spectrum is one of the most characteristic physical properties of the sample No solvent or matrix interferences and interactions are preshysent to contribute to difficulties in interpretation and identification
For a good infrared absorption spectrum one which accurately proshyvides the information needed however the analyst must take into account the intrinsic intensities of the bands in the sample spectrum and also the efshyfeet of sample thickness on band intensity The intensities of the absorption bands of different materials can vary appreciably For example nonpolar materials or compounds containing highly polar functions such as the carshybonyl group are moderate to strong absorbers Furthermore the thicker a sample (that is the greater the number of molecules along the radiation path which may interact with and absorb the incident radiation) the more intense the absorption bands Therefore one should expect to use different thicknesses for different samples to optimize the spectra obtained for the information needed
As a general rule nonpolar materials require a sample thickness in the vicinity of O I mm On the other hand thicknesses in the range from 002 mm (or thinner) to 005 mm will be required for polar materials
This experiment will familiarize the operator with the various technishyques for preparing samples of pure liquids
974
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
4-2
PROCEDURE
Part I Sealed Cell
Remove the two Teflon stoppers from the O 1 mm sealed cell and lay the cell on a flat surface with a pencil under one end as shown in Figure 4- 1 to facilitate filling withshyout formation of bubbles Draw about O 5 ml of carbon tetrachloride (WARNING Carbon tetrachloride is toxic) into the syringe and insert the syringe into the lower fitting of the cell Slowly fill the cell by gently deshypressing the plunger of the syringe Do not
Fig 4-1 - Correct way to force the plunger of the syringe as this may fill a sealed cell put excessive hydraulic pressure on the cell
and force the cell open break the amalgam seal and increase the cell thickness Watch the liquid as it fills the clear openshying it is advisable whenever possible to add 02 ml of sample in excess of that needed to cover the opening About 02 to 04 m1 should be required if the cell is properly filled Remove the syringe and insert a Teflon plug with a twisting motion into the same fitting then insert the second Teflon plug in the same manner into the other fitting If liquid fills the top port remove most of it with a of tissue If the port is left full when the second plug is inserted excessive pressure may distort or rupture the cell
Put a sheet of chart paper on the instrument without a cell in either cell holder Record an 10 baseline as described in Part I of the Procedure in Exshyperiment 1 Adjust the 10000 control to position the pen at 100 transmittance
FREQUENCY (CM) 4()00 3600 3200 2Il00 2400 2000 1800 1600 1400 1200 1000 800 600 00
Fig 4-2 - Carbon tetrachloride spectrum O 1 mm sealed cell
974
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 4- 3
FREQUENCY (CM) 4000 3600 3200 2800 2(00 2000 1800 1600 1-00 1200 1000 800 600 400
Fig 4- 3 - Carbon tetrachloride spectrum of reduced intensity because of bubbles in sealed cell (0 1 nun sealed cell)
on the chart then place the cell in the sample position of the instrument and record the carbon tetrachloride spectrum as described in Part II of the Proshycedure in Experiment 1 Remove the chart paper from the recorder and fill in the appropriate information on the upper part of the chart
lThe spectrum should resemble Figure 4-2 If the band near 770 crnshyhas a transmission of more than 2 500 examine the cell for bubbles The spectrum produced using a cell with bubbles is shown in Figure 4- 3 Compare this spectrum with Figure 4- 2 Note that the absorption bands in Figure 4- 3 are less intense i e they transmit more of the radiation This is because the instrument sees partly sample and partly air and air transmits more radiation than the sample Rerun the spectrum if necessary
Remove the sealed cell from the spectroshyphotometer and remove the Teflon plugs from the cell With the glass syringe withdraw the carbon tetrachloride from the cell then empty the syringe With the rubber syringe blow air first through the cell until the cell is dry then through the glass syringe until it is dry Now lay the cell down once again with one end slightly raised ready for filling (A push-pull technique using two syringes should be used to clean and dry cells less than 0075 mm thick One syringe is used to contain the solvent and the Fig 4-4 Use of two-
syringes to clean cellsother to generate a vacuum which pul1s the solvent through the cell (Fig 4-4) This technique less than 0075 mm thick
974
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
4-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
Fig 4-5 Carbon disulfide spectrurrl 01 rrlrrl sealed cell
is also often useful for filling thin cells)
Use the 1 rrl1 syringe to inject about 04 rrl1 of carbon disulfide into the cell
-~= ~===~___ NEOPRENE tl=Oiiii GASKET
=r==r=====JI---WINDOW
__-==-__~~------SPACER ~WINDOW
~ NEOPRENE~ ~ GASKET
BACK PLATE
4- 6 - Derrlountable cell as serrlbly diagrarrl
974
CAUTION Carbon disulfide is toxic extrerrlely volatile and very flarrlmab1e Handle it under a hood with no open flarrles or hot plates nearby where the fumes could contact therrl
Replace the Teflon plugs firrrlly (with a twisting motion) first in the lower fitting and then in the upper Place the cell in the instrument sample position and obtain a spectrum The specshytrUrrl produced should resemble that in Figure 4- 5
Carbon disulfide and carshybon tetrachloride are two of the rrlost common infrared solvents and they are generally used in conjunction to cover the spectral range of the Model 735 Carbon tetrachloride may be used from 4000 cm- 1 to 1230 cm-i while
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 4-5
carbon disulfide may be used from 1390 cm- 1 to 400 em-i Keep the spectra obtained for these materials in a permanent file they will be used in Experishyment 5 and may be useful as part of a general reference file
Part II - Demountable Cell - Use with Spacers
Place the back plate of the denlOuntable cell on a flat surface with the studs of the cell upwards as shown in Figure 4-6 Lay one of the rubber gasshykets on the cell back plate with the aperture in the gasket centered on the aperture in the back plate Now place one of the rectangular KBr windows on the rubber gasket (Handle the windows at their edges hands should be dry or finger cots should be used) Lay a 0025 mm spacer on the window (If the spacer is wrinkled place the second KBr window on it and press the window firmly to smooth out the spacer Remove the second window) With an eye dropper put two drops of indene on the lower window in the aperture of the spacer Place the second window on top of the spacer by bringing one end of the window into contact with the spacer first and then lowering the other end If the top window is lowered properly the indene will fill the opening in the spacer and no bubbles will appear Center the second rubber gasket on top of the windows place the front plate over the studs and firmly and evenly tighten the four nutsmiddot Excessive or uneven tightening of the four nuts may crack the windows Obtain the spectrum as described in Part 1 The positions of the bands noted in Figure 4-7 may be used for cbecking the frequency calibration of the instrument
Part III Demountable Cell - without Spacer
Begin as in Part lI but do not place a spacer on the surface of the lower window With an eye dropper place two drops of mineral oil (Nujol) on the surface of the window near the center Place the second window and rubber gasket on top If necessary use the top window to spread the oil on the bottom plate so there are no air spaces or bubbles CialDp the windows in place with the top plate and thumb nuts A sample pr epared in this manner as a very thin film is often called a capillary filnl
Obtain the spectrum as described in Part I and refer to Figure 4- 8 Save the spectrum for reference in Experiment 6 which describes the use of mineral oil as a medium for obtaining the spectra of solid powders
Mineral oil can be removed from the cell windows by wiping them with tis sue and rinsing off the residue with chloroform
Follo the same procedure to obtain a spectrum of perfluorohydrocarbon 011 as shown m Flg 4-9
Part IV - Demountable Cell - a Viscous Liquid
Begin as in Part II but do not place a spacer on the lower window Put a small amount of silicone grease on the lower window and with the second window smear the grease and press it into a thin film Put the
974
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 4-6
FREQUeNCY (CMl 4000 3600 3200 2900 2400 2000 1900 1600 1400 1200 1000 800 600 400
~O S MICltONSl
Fig 4-7 - Indene spectrunl 005 == denlountable cell
FReQUENCY (CMlt) 4000 3600 3200 2800 200 2000 1800 1600 1400 1200 1000 BOO 600 400
I I I
10 11 12 131t J6 b20 25 $I
Fig 4- 8 - Spectrunl of nlineral oil capillary filnl run in denlountable cell FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 4-9 - Spectrum of perfluorohydrocarbon oil capillary film run in demountable cell
974
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 4-7
FREQUENCY (CM) 000 3600 3200 2800 2000 1800 1600 1lt100 1200 1000 800
Fig 4-10 Spectrum of silicone grease smear run in demountable cell
second rubber gasket on the top window and clamp the windows firmly with the top plate and thumb nuts
Obtain the spectrum as described in Part 1 It should be similar to that shown in Figure 4-10 If so keep it for future reference If the absorpshytion bands are too strongly absorbing either tighten the thumb screws furshyther to thin the sample or disassemble the cell wipe one window clean and then reassemble the cell (Be sure to tighten the thumb screws evenly to avoid cracking the windows) Again obtain the spectrum and compare it with Figure 4-10
Silicone grease is a common impurity in many samples since it is often used as a lubricant
The cell windows can be cleaned of silicone grease by wiping them with a piece of tissue moistened with toluene Afterwards rinse them with petrolshyeum ether or toluene
974
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 5-1
EXPERIMENT 5
Spectra of Liquids and Solids in Solution
OBJECTIVE
To obtain the spectra of materials in solution and to demonstrate the effect of solvent absorption bands
MATERIALS
Carbon tetrachloride carbon disulfide toluene polystyrene xylene three 10 ml volumetric flasks three 1 ml syringes demountable cell with NaCl or KEr windows and 0025 rom spacers two 01 mm sealed cells (or demountshyable sealed cells with 01 rom spacer) rubber ear syringe
INTRODUCTION
Often the analyst will find it necessary to analyze samples in solushytion The samples may be received in solution or may have to be put into solution if the absorption bands of the pure materials are so exceptionally strong that their true shapes cannot be discerned however thin the pure sample
The spectra of samples in solution present problems not encountered with pure samples All heteronuclear molecules which include any solvent one might choose have an infrared spectrum In solutions the spectrum of the solvent adds to that of the sample and may interfere with observation of the sample bands In selecting a solvent therefore it is essential to know the characteristics of its spectrum The purpose of this experiment is to acshyquaint the operator with some of the common infrared solvents especially carbon tetrachloride and carbon disulfide which are most often used
There are at least three methods for overcoming in part the effects of interfering solvent absorption bands
1 Obtain the spectrum of the pure sample as a capillary film or in a thin (0025 mm path length) sealed or demountable cell
2 Change the solvent to one with bands that do not interfere with the sample bands Since all solvents have several absorption bands in the infrared it is generally not possible to obtain a complete spectrum free from intershyfering solvent bands The normal procedure is to use two or more solshyvents to cover the complete range If one compares the spectra of CC14 and CS2 obtained in Experiment 4 (Figures 4-2 and 4-3) one finds that in those regions where CCl4 interferes CSZ does not The converse is also true
974
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 5-2
3 Obtain a compensated spectrUIll of the sample by taking advantage of the optical null balancing system of the instrUIllent that is place a cell conshytaining pure solvent in the reference beam of the spectrophotometer When the spectrUIll of the solution is run the instrUIllent will then automatically compensate for the solvent absorption bands For the Perkin-Elmer Models 7XX X67 and X21 this technique is successful only in those regions where the solvent transmits more than 20
It is important when obtaining compensated spectra to bear in mind this requirement for no less than 20 transmittance anywhere in the solvent spectrum and to understand the reason for it For proper operation an optical null instrUIllent such as the Model 735 requires that a certain amount of radiant energy reach its detector When this minimum energy requirement is not satisfied the pen system will be sluggish and will not accurately follow the absorption behavior of the sample
A simple experiment with three opaque cards will demonstrate the effect of low energy With a white card partially block the sample beam of the instrument to make the pen indicate 15l0 (Think of this as a solvent abshysorption band that allows only 1500 transmittance) Holding the first card in position with masking tape use a second card to partially block the reference beam to bring the pen back up to about 95 Tape this card in place also (Think of this second card as the compensating solvent which eliminates the effects of the solvent in the sample solution) Now totally block the sample beam with a third card to simulate an absorbing sample and observe the pen behavior It will appear to move sluggishly and will go downscale rather slowly it will not be able to respond accurshyately to rapid changes in light transmission like those encountered when scanning a sample spectrUIll In the above experiment if a very strong solvent band were simulated by completely blocking both beams with the cards thus allowing no energy through either beam blocking the sample beam with a third card would not affect the pen position Under such conshyditions the recording system is said to be dead If
PROCEDURE
Part I - Solution of Liquid in a Liquid
Prepare 20 by volUIlle solutions of toluene in carbon tetrachloride and toluene in carbon disulfide in two 10 ml volumetric flasks by adding 2 ml of toluene to each flask with a glass syringe and diluting to the mark with carbon tetrachloride and carbon disulfide respectively
974
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 5- 3
Fill the O I mm sealed cell with the carbon tetrachloride solution as described in Experiment 4 and obtain the spectrum Compare this spectrum with that of carbon tetrachloride obtained in Experiment 4 and with the specshytrum of pure toluene shown in Figure 5-1 Note those spectral regions where the carbon tetrachloride absorption bands interfere
Leave the first cell in the sample beam and fill a second O 1 rom sealed cell with carbon tetrachloride Put it in the reference beam of the instrument and run a spectrum The instrument will automatically compensate for solvent absorption Again compare the spectrum with Figure 5-1 Note that there are regions in the compensated spectrum where either absorption bands have not been recorded or where the accuracy of the recorded band intensity and frequency is reduced Comparison with Figure 4- 2 will show that these reshygions correspond to the locations of the strong (less than 20 transmittance) solvent absorption bands
Remove both cells from the instrument and draw out the contents with a glass syringe Flush the cells with CC14 using the syringe and dry them by blowing air through them with the rubber syringe
Fill one of the cells with the CSZ solution and obtain the spectrum Compare this spectrum with that of CSZ obtained in Experiment 4 and with the spectrum of pure toluene shown in Figure 5-1 Note the regions where the CSZ absorption bands interfere with observation of the toluene absorption bands
Now run a compensated spectrum as described above for the CC14 solution Clean the cells and syringes
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1600 1600 1400 1200 1000 600 600 400
Fig 5-1 - Spectrum of pure toluene run in 0025 mm sealed cell
974
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 5-4
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12
Fig 5-2 Spectrum of 20 weight-to-volurne polystyrene in xylene run in a 0025 mm demountable cell
Part II - Solution in a Liquid
Prepare a solution of the polystyrene by placing 2g of polystyrene in a 10 ml volumetric flask and diluting to the mark with xylene Retain the solution for use in Experiment 8
Set up a demountable cell with a 0025 mm spacer as described in Experiment 4 With a dropper place 2 drops of the polysytrene solution on the window in the center of the spacer opening Place the second window on top of the spacer avoiding bubbles and clamp with the top plate and four thumb nuts Obtain a spectrum compare it with Figure 5-2 and retain it for comparison with that prepared in Experiment 8
Disassemble the cell Carefully clean the crystal windows and spacer by rinsing them with xylene and drying them with air
Reassemble the demountable cell with xylene as the sample Obtain the spectrum and compare it with the spectrum of polystyrene solution obshytained previously Note and mark those bands which do not belong to the xylene solvent and hence do belong to the polystyrene Clean the cell
974
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 6-1
EXPERIMENT 6
Spectrum of a Solid and Preparation of a Mull
OBJECTIVE
To obtain the infrared spectrum of a solid prepared as a mull in mineral oil and in perpoundluorohydrocarbon
MATERIALS
A 50 mm or 65 mm (o D) mullite or agate mortar and pestle (Perkin-Elmer part no 990-4906) mineral oil such as Nujol (Perkin-Elmer part no 186-2302) perfluorohydrocarbon such as Fluorolube (Perkin-Elmer part no 186-2301) or perchlorokerosene demountable cell with two KBr windows rubber policeman 2 4-dinitrophenylhydrazine phthalic anhydride talc (baby powder) sodium bicarbonate
INTRODUCTION
One of the most generally useful techniques for preparing a solid samshyple for infrared analysis is mulling Good results are obtained by this method only if the average particle size of the solid is somewhat less than the waveshylength of light the particles are to transmit or if the medium used to suspend the particles has nearly the same refractive index as the sample Since the latter is rarely (if ever) true one generally must reduce the average particle size of the sample to 1 or 2 microns If the sample particles are of this size when received or if the sample is quite frangible it may be placed directly on a crystal window a drop or two of mulling agent added and a second winshydow placed on top A circular and back-and-forth motion will disperse the sample in the mulling agent and the spectrum may be obtained directly On the other hand coarse or hard particles will require some grinding
The most common mulling agent is mineral oil which for many spectra can be used over the full wavelength range of the instrument Howshyever it may be desirable in some cases to use a perpoundluorohydrocarbon over the range from 400Cl cm- l to 1350 cm- l and mineral oil from 1380 cm- l to
l650 cm- See Experiment 4 for reference spectra of the two mulling agents Fig 4-8 and Fig 4-9
It is the purpose of this experiment to familiarize the experimenter with the techniques of grinding and mulling which have proven successful for preparation of samples for infrared examination
974
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 6-2
FREQUENCY (CM I 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
III bull [T~n ~~Ii~~ bullImiddot I
T ~ - T ]middotTmiddot~-I ~ V
~
I L~ iI I I Imiddot~middot bull lL~~ bull i 40I 1 ~ -l bulll
~J I 1~ 1
1 bull 20 II I bull 1 ~
I I Ii II11 L~ I Ji iI41 I0 1 iIiI
II
10 11 12131 16 1820 25
Fig 6-1 - Spectrum of talc Inulled in ITlineral oil
PROCEDURE
Part I - Mulling a Finely Divided Solid
Place about 10 ITlg of talc on the face of a KBr window Add one sITlall drop of ITlineral oil and place the second window on top without a spacer With a gentle circular and back-and-forth rubbing motion of the two windows evenly distribute the ITlixture between the windows The mixture should apshypear slightly translucent with no bubbles when properly prepared Cla=p the sandwich between the front and back plates of the deITlountable cell as described in Experiment 4 and obtain a spectrUITl Ideally the strongest absorption band should have a transITlis sion of 0 to 10 and should not be totally absorbing for more than 20 cm- 1 The spectTUITl obtained should reshyseITlble that shown in 6-1 If the bands are distorted as shown scheshymatically in Figure 6- 2 the particle size is too great and some of the radiashytion incident on the ITlull has been scattered out of the saITlp1e beam This efshyfect called Christiansen scattering indicates that the particle size must be reduced if a better spectrUITl is required Determine the bands due to the mineral oil froITl the spectrUITl of Nujol in Fig 4-8
Talc produces a very strong absorption spectrUITl and must be careshyfully cleaned from the cell windows to prevent contaITlmation of future samples Wipe the windows with a tissue then wash them several times with methylene chloride Run a spectrum of the cleaned windows to be sure they are clean
Part II - Mulling a Coarse Organic Solid
The reduction of particle size to an average diameter somewhat less than 25 ~ (4000 em-I) the short wavelength limit of the Model 735 is most important when
974
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 6-3
preparing a mull Proper preparation requires patience diligence and effort
There are two techniques for grinding dry grinding and wet grinding The former which applies to compounds
UJ ltgtknown to be relatively stable will be Z
~described here the latter which applies iiito those materials which may lose water z
or undergo crystalline modification will 0
be described in Experiment 7 Preparashy tion of KBr Discs Both techniques can be used to prepare either mulls or KBr
WAVELENGTH (MICRONS I discs depending to a great extent on the sample
Fig 6-2 - Typical band distor-The sample chosen here tion resulting from Christiansen
24-dinitrophenylhydrazine is partishy scattering Dotted line represhycularly difficult and if one succeeds sents normal band shape in preparing a good mull (and as a result a good spectrum) with it he should feel assured he has the technique well in hand As an alternative phthalic anhydride is somewhat easier to handle The mulling procedure for both materials is the same
Place an estimated 10 to 15 mg of 2 4-dinitrophenylhydrazine (or phthalic anhydride) in a 50 or 65 mm mullite (or agate) mortar Larger amounts of sample are more difficult to grind Break up the solid and disshytribute it over the surface of the mortar by light grinding with the pestle Now with a vigorous hard back-and-forth motion of the pestle grind the sample until it becomes firmly caked on the sides of the mortar and quite glossy in appearance This process may take from 2 to 10 minutes depending on the sample and the operator
When the caked glossy condition has been reached add a small drop of the mulling agent (either the perfluorohydrocarbon for the 4000 cm- l to 1350 cm- l region or mineral oil for the 1380 cm- 1 to 400 CIrl- 1 region) to the mortar Grind the saIrlple with a vigorous rotary motion until all the material is suspended in the mulling agent It Irlay be necessary to add an additional sIrlall drop of the Irlulling agent as this grinding is continued The ideal conshysistency of the final mixture is about that of Vaseline reg
Remove the mull from the mortar with a clean rubber policeman (these are often coated with talc and should be wetted with alcohol and wiped in order to clean them) and transfer it to a KBr plate Place a second window on top of the first and distribute the saIrlple evenly between the plates The mull should appear slightly translucent if properly prepared
middot974
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 6-4
4000 3600 I
3200 2800 2400 2000 I
FREQUENCY (eMj 1800 1600 1400 1200 1000 800 600 400
Fig 6-3 - Spectrum of 2 4-dinitrophenylhydrazine mull
FREQUENCY (CM~) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
Fig 6-4 - Spectrum of 2 4-dinitrophenylhydrazine mull showing band distortions characteristic of Christiansen scattering
Clamp the sandwich in a demountable cell in the normal fashion and obshytain a spectrum over the spectral range appropriate to the mulling agent
The resulting spectrum should be similar to that given in Figure 6- 3 1pound the absorption bands appear too strong the mull may be thinned somewhat by tightening the locking nuts on the demountable cell Figure 6-4 shows band distortions which are characteristic of the Christiansen scattering effect If such distortions are observed in the spectrum obtained then the grinding proshycess has not been mastered and should be repeated from the beginning with the dry material
974
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 6-5
FREQUENCY (CMmiddot) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 II 121314 16
Fig 6-5 - Spectrum of phthalic anhydride mulled in perfluorohydrocarbon
FREQUENCY (CM) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
(MICRONS) 10 11 12 13 I 16 18 2() 2S
Fig 6- 6 - Spectrum of phthalic anhydride mulled in mineral oil
Figures 6- 5 and 6- 6 show the spectra for phthalic anhydride mulled in perfluorohydrocarbon and in mineral oil respectively
Part III - Mulling a Coarse Inorganic Solid
Follow the procedure described in Part II but with a sample of sodium bicarbonate A spectrum similar to that shown in Figure 6-7 should be obshytained If band distortion occurs repeat the grinding of the dry material unshytil a satisfactory spectrum is produced
974
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 6-6
I FREQUENCY (CM) 4000 3000 3200 2800 20100 2000 1800 1600 1400 1200 1000 800 600 lt100
Fig 6- 7 - Spectrum of sodium bicarbonate mulled in mineral oil
974
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
7-1
EXPERIMENT 7
Spectra of Solids - the KBr Disc Technique
To obtain the infrared spectrum of a solid prepared in a potassiUITl bromide disc
MATERIALS
A 50 mm or 65 mm (0 D) mullite or agate mortar and pestle (990-4906) infrared quality 100 to 200 mesh KBr powder (990-5927) reagent grade ethanol toluidine red or phthalocyanine green pigment or benzoic acid (Sample I) small piece of quartz or granite (Sample II) 13 mm KBr die 13 mm KBr disc holder eye droppers balance capable of weighing I mg with good precision micro spatula vacuum system capable of providing 1 to 2 rnm vacuum 12 ton laboratory press small camels-hair brush tweezers
INTRODUCTION
Potassium bromide powder can be pressed at about 12 tons of force linto clear discs having high transmission throughout the 4000 to 400 cm- range
of the infrared instrument Before pressing samples may be mixed with the KBr powder at a sample concentration level of O 1 to 200 and their spectra obtained in the KBr matrix As in the mulling technique the sample must be very finely ground in order to reduce scattering losses and absorption band disshytortions This experiment demonstrates a wet-grinding method which has been found particularly effective for reducing the particle size of inorganic matershyials as well as some organic compounds As with the mulling technique the choice of wet or dry grinding depends on the sample and the quality of the spectrum desired by the operator
A word of caution concerning the KBr technique is required Modificashytions in the spectra of some samples may occur due to ion exchange with the KBr matrix pressure effects or transformations to other crystalline forms This does not detract from the general usefulness of the technique but must be kept in mind when comparing unknown spectra obtained as KBr discs with known or standard spectra obtained by other techniques
PROCEDURE
Part I - Preparation of a Blank KBr Disc
Place the body of the die on its base (Consult the instructions for the
Dry the KBr powder in an oven at 1050 for 12 hours and store it in a desiccator
974
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 7-2
FREQUENCY (eM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 0100
Fig 7-1 - Spectrmn of potassimn bromide disc blank
particular die for a description of the die parts and directions for pressing a disc) Insert the small lower ram into the die opening with the shiny surface up Completely transfer 300 ~5 mg of infrared quality KBr powder to the die opening (Use the of a carriels-hair brush to brush the KBr powder from its container) Insert the top plunger and with a light rotary motion of the plunger level the sample Connect the die to the vacumn system and evacuate the die to a pressure of I to 2 rrirn of Hg for about 2 minutes to remove lightly held water from the surface of the KBr and to remove air from between the KBr particles With the vacumn still connected place the die on the press with the top platen if required on top of the ram Press for 3-4 minutes at 10 to 12 tons of total force Disconnect the die from the vacumn line reshylieve the pressure on the press and remove the die Invert the die and remove the base Place the inverted die back in the press and center the split ring on the die so that the lower plunger will be visible when forced from the die Now with the press force the plunger upward until the lower ram and disc just clear the body of the die Remove the die from the press and with the tweezers place the disc which should be homogeneous in appearance in the disc holder Insert the disc holder in the instrmnent and obtain the spectrmn in the usual manner The spectrmn should resemble that shown in Figure 7-1
Part II - Wet Grinding of Samples and Preparation of a KBr Disc
Place an estimated 10 to 15 mg of Sample I (see materials list) in the mullite or agate mortar With the eye dropper add 10 to 15 drops of ethanol to the mortar Grind the sample with a vigorous firm rotary motion reshystricting the sample as much as possible to about 13 to 12 of the mortar surface until the ethanol evaporates completely Do not continue grinding after the sample becomes dry If samples are particularly hard the wet grinding step may be repeated
974
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 7-3
FREQUENCY (CM) 4000 3200 2800 2400 2000 IOO 1600 1400 1200 1000 800 400
4000
Fig
3600
7-2 - Spectrum of benzoic acid in potassium bromide disc
FREQUENCY (CM) 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
4000
Fig 7-3 - Spectrum of benzoic acid in potas sium bromide disc showing band distortions caused by poor grinding
FREQUENCY (CM) 3600 2800 2400 2000 1800 1600 1400 1200 1000 800 400
Fig 7-4 - Spectrum of quartz in potassium bromide disc
974
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 7-4
Scrape the ground sample from the sides of the mortar with the micro spatula and weigh out 1 ITlg (l2 34 mg for toluidine red) on an appropriate balance Place the weighed ground sample in a clean ITlortar Weigh 300 S ITlg of dry KBr powder and add 5 to 10 ITlg to the mortar containing the samshyple Use the pestle to mix the KBr and sample with a gentle rubbing motion Do not grind the KBr during the ITlixing procedure since reduction in particle size is not required and will lead to adsorption of water on the KBr Now add 15 ITlg of KBr powder and mix as before Add another amount of KBr approxishyITlately equal to the total quantity in the mortar (1 e add about 30 ITlg) and mix Continue adding and ITlixing KBr in this manner until all the KBr is in the mortar If this procedure is followed a homogeneous mixture of the samshyple and KBr with little water pickup on the KBr will result If the sample is stable when heated the mixture may be dried in an oven or vacuum oven for 1 hour at 105 to 1100 C
Completely transfer the mixture from the mortar to the die using the side of the camels-hair brush and press the disc as described in Part I Remove the disc froITl the die ITlount it in the KBr disc holder and obtain the spectrum It should resemble that shown in Figure 7- 2 If it exhibits the band distortions evident in Figure 7 - 3 then the grinding was not done proshyperly and a new saITlple ITlust be ground and incorporated into a new KBr disc
Part III - Preparation of an Inorganic Sample in a KBr Disc
Place 10 to 15 ITlg of SaITlple II in the mortar and grind it as described above Prepare the 300 ITlg KBr disc using 1 mg of ground saITlple press it as described and obtain the spectruITl The spectrum should be siITlilar to that shown in Figure 7-4 and should not exhibit distortion due to the scattering effect of large particles Quartz is a relatively hard sample to grind and the 10 to 15 mg saITlple may have to be wet-ground twice before the KBr disc is prepared
For quantitative analysis an electronic ultramicrobalance such as
reg the Perkin-Elmer Autobalance could be used If a microbalance is not available it may be desirable to weigh out 3 mg of sample mix it with 1 gram of KBr and then take a 300 mg aliquot for preshyparation of the KBr disc
974
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 8-1
EXPERIMENT 8
Spectrum of a Solid Prepared as a Film from Solution
OBJECTIVE
The preparation of a solvent-free film of solid sample from solution in a volatile solvent
MATERIALS
The polystyrene solution used in Experiment 5 demountable cell KBr windows for the demountable cell eye dropper hot plate paper toweL
INTRODUCTION
Solution spectra will satisfy the requirements of many analyses partishycularly in quantitative work but in some cases they suffer from the disadvanshytages of overlapping and interfering solvent absorptions In situations where the analyst can choose the solvent used these disadvantages can be largely overcome as when CSZ and CC14 are used in conjunction to cover the full range of the instrument At times however it is not possible to select the solvent in which the solid of interest occurs and the analyst must accept the solution as received Typical examplemiddots are samples of solvent- based paint or varnish Where possible therefore it is desirable to remove the solvent interferences and to obtain a spectrum of the solute only This experiment describes the procedures for preparing pure solid samples from solutions containing volashytile solvents
PROCEDURE
Part I Preparation of a Film from Solution in a Volatile Solvent
Turn the hot plate on and select a temperature which is quite warm to the touch but not hot The KBr windows may crack if the hot plate is set at too high a temperature Place a paper towel on the hot plate and a KBr winshydow on the toweL With the dropper add two to three drops of the polystyrene solution to the surface of the window while it is still cool Allow the solution to spread over the face of the crystal and evaporate completely Some Inatershyials retain solvent rather tenaciously and the analyst should allow several Ininutes for complete evaporation of the solvent The objective in this proshycedure is to obtain a fi1In having a thickness in the range of 003 to 007 rnm
When the poundi1In appears to be free of solvent place the window in a demountable cell add a second window if necessary to claInp the first firInly and obtain the spectrum The resulting spectrum should be siInilar to that shown in Figure 8-1 Compare this spectrum with the solution spectrum
974
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 8-2
FREQUENCY (eMmiddot) 000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
10 11 12 13 1lt1 16 18 20 D
Fig 8-1 - Spectr= of polystyrene cast film
obtained in Experiment 5 If the bands produced by the film are appreciably stronger than those in Figure 8-1 too much solution was used and the preparashytion must be repeated if the bands are too weak more solution should be evaporated on the crystal Examine the spectr= critically for solvent abshysorption bands Consult the spectrum obtained in Experiment 5 Part II for the positions of the strong solvent bands
974
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 9-1
EXPERIMENT 9
Quantitative Analysis
OBJECTIVE
To i11ustrate the procedures and techniques of quantitative infrared spectroscopy
MATERIALS
Sealed cells (0015 and 0025 mm) hypodermic syringes graph paper isopropyl alcohol toluene and methyl ethyl ketone
INTRODUCTION
The amount of sample present in the sample beam of an infrared spectroshyphotometer is directly related to the strength of an absorption band (or the absorbance at any given frequency) in the infrared spectrum of the sample The relation is expressed mathematically in terms of sample concentrashytion and radiation path length through the sample by the Beer-Lambert Law Depending on the units of measurement this law may be expressed in a variety of ways
1 100 Absorbance = A =
eel sectbc=log I = log T log Tmol wt
Where A = absorbance observed from the spectrum (Figures 9-1 and 9-2)
e =molar absorptivity or molar extinction coefficient It is a characteristic of the sample at a particular frequency It is often nearly the same for a group of compounds if the absorption band is characteristic of that group
c = concentration in grams per liter
l=b = sample path length in cm (inside cell thickness)
a = absorptivity characteristic of the compound for that particular absorption ~ = emol wt
= intensity of incident radiation (Figures 9-1 and 9-2)
974
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 9-2
02 A Ii I pound03 ~O4
05
06 07
~~ 2ll~dddkblIdd=i=l=bbb6
FREOUENCY_
Fig 9-1 - Absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
70 K+III++1++1-~-t - 60 t ~50pt+III++1+~-t-~ ~OK+III++1++-t-t-+1 laquo ~30
20
10 ALOGtLOG~LOG~LOG 606~O~8 OLL~~~__~~~~~~~~~
FREQUENCY_
Fig 9-2 - A second example of an absorption band recorded on a linear transmittance scale and on a nonlinear absorbance scale
I = intensity of transmitted radiation (Figures 9-1 and 9-2)
T =transmittance =110
or the ratio of the radiant energy transmitted to the radiant energy incident on the sample
Most infrared spectrophotometers record the spectrum linearly in transmittance units and nonlinearly in absorbance units In order
974
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 9-3
to relate such spectra directly to concentration the transmittance measurements must be converted to absorbance units This can be done either by (l) mathematical conversion (2) using chart paper having a nonlinear absorbance scale as in the second parts of Figures 9-1 and 9-2 or (3) using a special ruler calibrated in absorbance units which has the same length as the transmittance scale on the chart paper
Usually for quantitative analysis by infrared spectroscopy the abshysorptivity a or e is not calculated Instead a standard is preshypared whichcontains a known concentration Cs of the compound in the unknown The absorbance As of the standard is measured at the same frequency that is used to measure the absorbance of the unknown A The concentration of the unknown Cu in a binary mixture can theVt be calculated from a simple proportion as follows
A a C 1 C 1 u - uu uu
T=aCl =Cl s - s s s s
If the same cell or cells of exactly the same path length are used to obtain the spectra of the standard and unknown then the proportion becomes AulAs = CuCs The concentration of the unknown can then be determined from the expression C u = AulAsCs
This equation demonstrates that the Beer-Lambert Law allows the use of any units of concentration such as percent by volume pershycent by weight or mole fraction so long as the units used in the calculations and determinations are the same as those used in the calibrations Moles per liter or grams per liter need only be used when either e the molar extinction coefficient or the absorptivity is used
Often a graph of absorbance versus concentration is plotted (see Figures 9-12 and 9-13) particularly if the unknowns are expected to fall into a wide concentration range or if the analysis is to be repeated but the standardization is not Determining the concentration of the unknown then becomes a simple matter of measuring the absorbance at the freshyquency used in preparing the graph and reading the corresponding conshycentration from the graph A linear plot may also be obtained by plotting transmittance T-IIo versus concentration on semilog paper (see Figure 9-14)
It is sometimes difficult to determine the value of transmittance (10 )
or absorbance (A2) at the base of an absorption band because of the close proximity or actual overlap of other bands For best preshycision it is preferable to use a horizontal baseline as shown for bands a band c in Figure 9-3
974
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 9-4
Fig 9-3 - 10 for complex absorption bands Dotted lines showextenshysion of bands in an assumed symmetrical Lorentzian shape
When a point is selected for determining the value of I or AI it is prefshyerable that it fall between 20 and 8500 transmittance (07 and 01 absorbshyance units) Also even though such a point is not always taken at an abshysorption maximum (transmittance minimum) in quantitative analysis it is best to use an absorption maximum because it is easily located and the spectrophotometer servo system is in equilibrium at that point
In any but the crudest quantitative analysis it is necessary to determine T (or A the band absorbance) for all samples (unknowns and standards) from several spectra A good procedure is to start with two spectra for each sample If the values determined for roT differ by more than 100 obtain another spectrum If the three values for T vary by more than 200 make still another determination from a fourth spectrum The T value to be used is the average of all the determinations made
Prepare the absorbance vs concentration (calibration) curves using the same instrument that will be used to analyze the unknowns Use the same cell and instrument operating conditions for the standard and unknown solutions If this is inconvenient use fixed thickness cells (Experiment 4) of accurately determined dimensions (Exshyperiment 3) and make corrections for any difference in thickness beshytween the cell used for the standard solutions and the cell used for the unknown solutions Errors from the distortion or rupture of cells due to improper cell handling techniques are very Significant in quantitative
974
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 9-5
analysis Use care when filling and cleaning cells (see pages 4-2 and 4-3)
The following data show how a solution can be quantitatively analyzed The specific example is a ternary solution of toluene isopropyl alcohol and methyl ethyl ketone which is widely used in the paint and adhesives industries
Figures 9-4 9-5 and 9-6 are spectra of toluene isopropyl alcohol and methyl ethyl ketone respectively Figures 9-7 through 9-11 are spectra of solutions of these three liquids at various concentrations (expressed in percent by volume) The absorption band at 817 cm- 1 is conveniently used for all calibrations and determinations of isopropyl alcohol and the absorption at 695 cm- 1 is used for toluene The methyl ethyl ketone is determined by difference
fREQUENCY (CM 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600
bull 10 n 121314161120 25
Fig 9-4 Spectrum of neat toluene in a 0015 mm KBr cell
4000 3600 3200 2800 2400 2000 FREQUENCY (CM)
1800 1600 1400 1200 1000 800 600
10 11 12 t~I 1120 2S
Fig 9-5 Spectrum of neat 2-isopropyl alcohol in a O 015mm KBr cell
974
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 9-6 FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
-I -I ~Hlj
~ I w U z laquo
i I -- l tshy~
~ il I I~ -f Ii t- i ~ -II I-shy
II ~ ~--l11 2
it I 1NJl1 iii j i ~ i Ii 11+H i
i I Ii 1 II i il jifll I ishy
i
fMl r hit ill 11 LIil i ~+ 1 Il 0 m Iii i I
2
rtH- i
f T +HltttiflH~ctfH+++t++ttffi-t++l+htttFmiddotJ If ~- i i ~ ii bull t ~ I i ~ 1fl
I I I T f 1+ J l( ~ i iij 1i J ~
j
(MOONS) n Fig 9-6 - Spectrum of neat methyl ethyl ketone in a 0015 mm
KBr cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
~ H+++1It+tttHHtti+ttttt++++++ttHttlf-oifj~ iHtl~ I ill I j I liV~ ~ 11ttt++++fu+ttt-t+-t++1+t+HH+++++++++++++HttttHH-tHtftHlt IWhH f 41 I I I i
117
I Iit- ill~ illl til lji I 14tl c fi
- fIT
IIH+H+iH+i+++++++++-lfHcH++t+H+H+iH+i-++ltt+ttH11t+HII+H+It+r LHI II 111l II i 1
bull o 1- -l--t shyt lilii III 25 5 (MIClONS) n 20
Fig 9-7 - Spectrum of solution containing 15 isopropyl alcohol 55 toluene and 30 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
+ 1 1 _ _~ J ~ftJ I j~ lAi i Ie j i i II I J II j II r- I I I II I I I I I
1 1 I I it Iii III
ii 0 Itbull I 10 11 12 13 1 16 8 20 2S
Fig 9-8 - Spectrum of solution containing 2000 isopropyl alcohol 45 toluene and 35 methyl ethyl ketone in a 0025 mm cell
974
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 9-7 FREQUENCY (CMl
~ooo 3600 3200 2800 2~00 2000 1800 1600 1~ 1200 1000 800 600 400
Fig 9-9 - Spectrum of solution containing 2500 isopropyl alcohol 4400 toluene and 31 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 200 2000 1800 1600 1 00 1200 1000 800 600
Fig 9-10 - Spectrum of solution containing 3500 isopropyl alcohol 2000
toluene and 4500 methyl ethyl ketone in a 0025 mm cell
FREQUENCY (CM) 000 3600 3200 2800 1400 2000 1800 1600 1~ 1200 1000 800 600
Fig 9-11 - Spectrum of solution containing 50 isopropyl alcohol 1400 toluene and 3600 methyl ethyl ketone in a 0025 mm cell
974
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
0800
0700
0600
0500 w u z lt
~ 0400
51 ~
0300
0200
0100
ISOO
1400
1200
1000 w u z lt(
~ 0800 o fJ) m lt 0600
0400
0200
0-----10---20 0 40 ~5LO----l60 o 10 20 30 40
BY VOLUME TOLUENE BY VOLUME ISOPROPYL ALCOHOL
Fig 9-13 - Plot of volume percent isopropyl alcohol vs absorbance toluene vs absorbance obtained from obtained from 817 cm-1 absorption 695 cm- 1 absorption band in Figs 9-7
band in Figs 9-7 through 9-11 through 9-11
Fig 9-12 - Plot of volume per~ent
PROCEDURE
Laboratory Analysis of a Ternary Solution
Prepare accurately the following solutions ( by volume)
Solution Isopropyl Alcohol Toluene Methyl Ethyl Ketone
A 15 50 35
B 23 27 50
C 40 20 40
D 70 10 20
Obtain at least two spectra for each solution determine A or T for toluene (at 695 cm- 1) and isopropyl alcohol (at 817 cm- I ) in each solution and preshypare plots of absorbance vs concentration on linear graph paper (or 00 transmittance vs concentration on semilog paper) as shown in Figure 9-12 (or 9-14) for each solvent Now obtain at least two spectra of a solution containing the three solvents in an unknown proportion (As a check on results have a coworker make up the unknown solution with accurately measured quantities of each solvent and have him or her record the
974
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Page 9-9
composition for comparison with the experimental results) Deshytermine A or T for toluene and isopropyl alcohol from the spectra of the unknown and using the calshyibration curve plotted from the standard soLutions determine the composition of the unknown solution
Important Do not use the curves given in Figures 9-12 through 9-14 to determine the composition of your unknown Calibration data must be obtained from the spectrophotometer that is used to measure the absorbance of the unknown if reliably accurate results are to be obtained Even different instruments of the same model may not yield sufficient accuracy although results will generally be better than those obtained from different models
90
80
70
60 IampJ U Z 50 ~ If) Z 40 laquo a lshy
i
30
200 10 20 30 40 50
BY VOLUME ISOPROPYL ALCOHOL
Fig 9-14 - Semilog plot of percent T VB volume percent isoprryl alcohol as obtained from 817 cm- absorption band in Figs 9-7 through 9-11
974
60
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
Absorption in Different Regions of the Infrared Spectrwn
FREQUENCY (CM)
4000 3600 3200 2800 2400 2000 1 800 1600 1400 1200 1000 800 650 1 J100
H_
Hydrogen Stretchin~ f-J-- Hydrogen Bending90
VHI ~ _11 ~O~ ~t YH VH~ It H~ ~ +shy80 ~t t~p1J I C-H IT middotmiddotmiddotl~t~It--middotf-- r---_ ---- f---- f--middot~yenrmiddot--middot~
70 r-shy - I i~T ~~ J C=O 1 Sin Ie-Bond Stretch
~ 60 UI~ sclP4middot1- S~ellllt ~t ect~~ e c~ _~= ~ ~~~f+~ht--r-r--~~4 0 U Hio- ~Lltfmiddotmiddot -- ~ I C-ClLJVU
~ 50 Associated N-H OH J 8=0 C=8 L_il CL_r-shy
~ ~ + i l e== I 2SIU Do ble~ ond Stre ch St etcl E I C h~L_ Igt 1- - ~ U) 40 +- _ t-- f~+- 1-f1ll- tffU-middotImiddotmiddotmiddot bull C I n C --- bull
Z I L Ii ~~ ~-~ ~ I [ S
~ 30 r r 1 1 [ I~t t~~ B~ ____ r---t- -_m I nnn_ __ I S4 shy f4-~ -ot- fonj lgatE d an Ar mat c Dc uble 18trtotch
20 H I ~ 1 N-H I + N-H I r------l-- ~_ bull leone StIdchhr~~ s hr Nfst I - til If s 1 elf ~ ~ L C-F J 10 I+r-I-
E
I ~ -r---1
C=N N=O I jC~Sin~le4nd$ret4L-i-+--i t if - I 1 bull N pouhhe-B nd1 bull o 1 ltrh
~ d l1
~
~ I)Q (l)
gtshy
974
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
NRC BULLETIN No 6
NATIONAL RESEARCH
COUNCIL
OTTAWA 1959
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP
FREQUENCIES
RN JONES
REPRINTEO BY THE PERKIN-ELMER CORPORATION WITH THE PERMISSION OF THE NATIONAL RESEARCH COUNCIL OTTAWA CANADA
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
CONTENTS
I Introduction
II Characteristic Group Frequencies of Hydrocarbons
1 3600 - 1700 cm -1 Chart I lII 1700 - 700 cm- Chart II
III Characteristic Group Frequencies of Oxygenated Compounds
1 3700 - 2000 cm -1 Chart III II 2000 - 800 cm -1 Chart IV
IV Characteristic Group Frequencies of Nitrogen Phosphorus and Sulfur Compounds
11 3600 - 1700 cm- Chart V II 1700 - 900 cm -1 Chart VI
V Overtone Bands of Substituted Benzenes Table I
VI C = C Stretching Bands of Linear Olefins Table II
VII C - H Out-of-plane Bending Bands of Linear Olefins Table III
VIII C - H Out-of-plane Bending Bands of Substituted Benzenes Table IV
IX Carbonyl C = 0 Stretching Bands Table V
X Bibliography
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
INFRARED SPECTRA OF ORGANIC COMPOUNDS
SUMMARY CHARTS OF PRINCIPAL GROUP FREQUENCIES
INTRODUCTION
During the past decade the literature on the infrared spectra of organic compounds has expanded at an ever increasing rate and much of this work has been concerned with establishing charactershyistic group frequencies These data have been summarized and critically reviewed in recent monographs by Bellamy (1) BrUgel (2) Jones and Sandorfy (3) and Lecomte (4) They have also been tabushylated in a more condensed form in the widely used Colthup Chart (5) which has passed through several revisions since its first pubshylication
In these articles the authors have endeavored to bring together complete collections of the structure-spectra correlations and the newcomer to the field is liable to be overwhelmed when first conshyfronted by such a formidable mass of semi-empirical data
The Charts publish~d in this Bulletin make no pretense at such a complete coverage of the subject They were initially prepared in connection with an introductory course of lectures on chemical specshytroscopy given recently at Ottawa University The correlations to be included were selected as the Inost commonly used in this laboratory and their choice probably reflects to some extent our preoccupation with the structural identification of naturally occurring organic comshypounds and their degradation products
In the three series of charts the characteristic group frequenshycies associated with hydrocarbons oxygenated compounds and comshypounds containing other elements are dealt with separately The student is advised first to memorize the individual charts separately and then to integrate them to obtain the overall picture
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
In Tables I - V more detailed sub-divisions of the more imporshytant group assignments are given It must be stressed that the ranges given in these Tables are only representative values they are based on measurements made on pure liquids or on solutions in
carbon tetrachloride or carbon disulfide The possibility of variashytions outside of these ranges must be kept in mind and the chemist should read the appropriate sections of the texts cited above here these group assignments are critically evaluated
Finally as he becomes increasingly familiar with these corshyrelations the student can amplify and extend them by consulting the more detailed texts
R N Jones Division of Pure Chemistry National Research Council
April lOth 1959
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
CHART I
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - I
3500 em-I 3000 2500 2000
I I I It =pound1 121111 II d ~ III = 3300 i
CIIC-H 3100-3000
C=C-He -H st~t~hl ltgt-H
-c-cshyc
H2
CHlIX
CH2 X2
[C~~~tchl
2260- 2190
R-Ci5C-R+ r IC II C s tretchl
2140-2100
R-Ci5C-H
rc=~t~hJ
1980
c-c-c - -
C=C stretch 3000- 2800
2000- 1650 -CH2 shy
AROMATIC OVERTONES -CHa
C - H out of plone=HS~ bend
SEE TABLE r
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
CHART II
CHARACTERISTIC GROUP FREQUENCIES OF HYDROCARBONS - n
1700 em-I 1500 1300 1100 900 700
ICaC stretch I 1600 (APPROXl
AROMATIC RING
1 1380-1375
CHI
SYM1680-1650
C-C
NON shy CONJUGATEO
NON-CYCLIC
1467
ALIPHATIC CHe
1455
ALICYCLIC
CH
IC---b ~ ~ II
I C=C stretcn I SEE TABLE ]I
Iscillor I 1500 APPROX
AROMATIC
RING1680-1580
C-C CYCLIC
C-C-C-C
1420-1406 C- CHI
C-H in plone
bend
IZZZZ1J 1070
gtC -c-olt Ilym slretch I
IOUi017
0-C--oshy
~ 870-670
AROMATIC
RING
out of plone
C-H bend
SEE TABLE III
980-690
O-C-H
out of plone
C-H bend 720-718
1390-1360 SEE TABLE m -(OH 1shyDOUBLET 1i4
1460 GEM-DIMETHYLIskeletol ASYM IC-H rock I
ISOPROPYL CH
TERT BUTYL IC=H Igt~~dl Iym CH
bend
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
CHART m
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS -I
3500 3000 2500 2000
I I I I I I I I I 17777777771 7777 77777 t 5~St1 t tit I
in
3I~ZZ~fTmiddotWf free O-H 3500-3300stretch I
bonded O-H stretch in3635-PR polymers3623- SEC
3615 - TERT
3615-PHENOL
I 3600-3500
o -H stretch
Tr band
complex
35003480
I~i
O-H stretch
alcohol
dimer
3050-2990
C-H stretch
in epoxides
H H C--C
0 (weak)
1-LLo III bonded 0- H
stretch in
carboxyli c acid
dimersenolized
B-diketones
tropolones etc
1
2832-2815 C-H stretch
C-H stretch olciehydes
in methoxy
compounds
2720
265012400
0-0 stretch in deuterate d
alcohols
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
CHART III
CHARACTERISTIC GROUP FREQUENCIES OF OXYGENATED COMPOUNDS - n
1950 1600 I I
carbonyl C= 0 streich
TABLE l1
1600 1400 1200 1000 800 I I I I I Iaxr-= ~~I I~I II i 2ili If
1610-1550 1430-1400
carboxylate ion a melhylene
C-H scissor0 osym C~O - slrelcgt in lIetones and
esters
I 1420 -1390
o-H bend in
alcohols
(very weak)
I bull
1270-1150
o -C-O-R
streIch In
estrs
1270 cent-COOR
1257 -12 32 CH COOR
1218 - 1204 CHa COOC= C-R
1200 - 1190 R - COOR
1185 -1175 H - COOR
1175-1155 R-COOCH
I 1275-1010
R-0- R Qsym streIch in ether
t275 - 1200 CONJUGATED
1260 -1200 AROMATIC
1150 - 1070 ALIPHATIC
1000
1i~9 H stretch in alcohols
leoo PHE~OLS
1150-1140 TERT
1120-1100 SEC
1075 1010 PRIMARY
1100-1000 CYCLOHEXANOL TYPE
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
CHART J[
CHARACTERISTIC GROUP FREQUENCIES OF NITROGEN PHOSPHORUS SULFUR COMPOUNDS shy
2500 2000 I I
3530 shy 3400
free NmiddotH
stretch
-NHZ (2 BANDS
ASYM AND SYMl
(AMINES AND AMIOES)
= +
2600- 2550
2900-2300
bonded N - H stretch in
quaternary amine salts
(SEVERAL BANDS
rtJrzzzJl]~bull1
=
2270
R-N=C=O stretch
2250-2225
R-C=N
3500 cm- 3000 I I I
t 3500-3060
bonded N - H
stretch
I0 + shy
R-N=N=N stretch
2180- 2120COMPLEX SPECTRUM))NH (I BAND)
(AMINES AND AMIOES)
+R-NC
I
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
CHART n
CHARACTERISTIC GROUP FREQUENCIES OF
NITROGEN PHOSPHORUS SULFUR COMPOUNDS - 1I
1700 cm- I 600 1500 1400 1300 1200 1100 1000 900 I I I I I I I I
= IZZZ2l =t
~----i i =lZIIIIZ=
PI 2 22 nUl Z2 UU un 1370 _ 1250
k22272ZZ 2 u224 1680-1430
t U f m ~ ~ ~IN_ 0
I o~ 1 24o-H 0
1680- 1630
1650- 1500 (CIS AND TRANS 1300 -1250 0 - N0 2 I P -0 stretch 1IC- N stretchl [ m 0 2 BANOS) 1300-1250 N-NOt _ P-O-ArI - N osym stretch bull
O 1600-1500 C-N=O
1650-1600 -a-NOz 1500- 1430 N-N=O 1630-1550 -N-NOz 1570-1500 -C-N02
1060-1040
1- S = 0 stretch I R
S=OR
1050- 990
IP - 0 stretch I -P-O-R
1335-1310 1160-1130
1650-1590 1650-1475 0 S It asym stretch sym stretch
IAMIDE II I1 R S fO RSO1715-1630 1650-1580 R-CO-NH2 R 0 R ~O
C=O stretch 1580-1475 R-CO-NHR
AMIDE I
1715 -1675 R -CO-NHe
1710 - 1630 R -CO - NHR
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
TABLE I
OVERTONE BANDS OF SUBSTITUTED BENZENES
I 3 01 14-01
~
JV
i
1 1L ~~~~~I I I ~I~~~~
1900 1100 1900 1700 1900 1700
WAVE
I 23 TRI 135-TRI 124-TRI
) lJJ 234 -TETRA I 1245-TTRA I 11235-TETRA
jIJ ~ ) ~~~~~I I~~~~~ ~~~~~
1900 1700 1900 1700 1900 1700
NUMBER (em-I)
MONO
n
t z o J I shy0 0 o VI CD lt[
I 2 01
If n ~
PENTA HEXA
1 )
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
TABLE II
C=C STRETCHING BANDS OF LINEAR OLEFINS
Rl H RI Re
C=C 1678-1668 em-I 1662-1652C =C H Re H H
R H RI H
C=C 1675-1665 C=C 1658-1648 R2 Ra Re H
R RS R H
C=C 1675-1665 c =C 1648-1638 Re R4 H H
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
TABLE m
C-H OUT-OF-PLANE BENDING BANDS OF LINEAR OLEFINS
R H R Rs 995-985 em-I 840-790 C =C 910-905 C=C
H H R2 H
RI H R R2c =C ~ 980-965 c=c~ ~690
H R H H2
R H C=C 895-885 R2 H
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
TABLE IV
C H OUT-OF-PLANE BENDING BANDS OF BENZENE DERIVATIVES
Benzene Monosubstituted benzene 12-Disubstituted 13 -Disubstituted 14-Disubstituted 123-Trisubstituted 124-Trisubstituted 135 -Trisubstituted 1234-Tetrasubstituted 1235-Tetrasubstituted 1245-Tetrasubstituted Pentasubstituted
Five adjacent free hydrogen atoms Four adjacent free hydrogen atoms Three adjacent free hydrogen atoms Two adjacent free hydrogen atoms One free hydrogen atom
671 cm- 1
770-730 770 -735 810-750 833-810 780 -760 825-805 865-810 810 -800 850 -S40 870 -855
870
770 -730 770 -735 810-750 86O-S00 900-860
710 -690
710 -690
745-705 885-870 730-675
710-690
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
TABLE V
PRINCIPAL CARBONYL C = 0 STRETCHING BANDS (cm -1)
KETONES
R - CO - R R - C = C - CO - R R - CO - Ar Ar - CO - Ar R - CO - CO - R R - CO - CHZ - CO - R (enolized) Sat cyclic (six membered or larger ring) Sat cyclic (five membered ring) Sat cyclic (four membered ring) Quinones (Z carbonyl groups in same ring) Quinones (2 carbonyl groups in different ri1 copolone s
1725 -1705 1685 - 1660 1700 - 1680 1670-1660 1730-1710 1640 shy 1540
ngs) 1600
1725 1750 1775 1690 1655
- 1705 - 1740
- 1660 - 1635
ALDEHYDES
Usually about 15 cm -1 above corresponding ketones
ACIDS
R - COOH (dimer) R - C = C - COOH (dimer) Ar - COOH
1725 -1700 1715 -1690 1700 - 1680
ESTERS
R - COOR R - C = C - COOR Ar - COOR R - COOAr R - CO OC = C - R Sat Y-Lactone Sat O-Lactone
1750-1735 1730 -1715 1730-1715 1800 - 1770 1800 shy 1770 1780 shy 1760 1750 - 1735
OTHER CARBONYL COMPOUNDS
R - CO Cl R - CO - 0 - CO - R Cyclic anhydride (5-membered ring) R - CO - 0 - 0 - CO - R Ar - CO - 0 - 0 - CO - Ar R - CO - NH Z R - CO - NHR
1815-1770 1850 - 1800 1870 - 18Z0 1820 -1810 1805-1780 1690 shy 1650 1680 -1630
and 1790 and 1800 and 1800 and 1785
- 1740 - 1750 -1780 -1755
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950
BIBLIOGRAPHY
(1) L J Bellamy liThe Infra-red Spectra of Complex Molecules Second Edition Methuen amp Co (London) John Wiley amp Sons (New York) 1958
(2) W BrUgel Einfuhrung in die Ultrarotspectroskopie ll Steinkopffbull
(Darmstadt) 1954
(3) R N Jones and C Sandorfy The Application of Infrared and Raman Spectrometry to theElucidation of MOlecular Strucshyture Technique of Organic Chemistry A Weissberger ed Vol IX Interscience Publishers Inc (New York London) 1956
(4) J Lecomte Spectroscopie dans lInfrarouge Handbuch der Physik S FIUgge ed Vol XXVI Springer-Verlag (Berlin Gtlttingen Heidelberg) 1958
(5) N B Colthup J Opt Soc Am 40 397 1950