تشخيص الطيفي نظري –مرحله الرابعة –كلية العلوم / قسم الكيمياء

د. هالة الزهاوي .أ

المحاضرة االولى

-Spectroscopic Identification

1) Silverstein - Spectrometric Identification of Organic Compounds 6th 2) Harris, D. C., Bertolucci, M. D., Symmetry and Spectroscopy, Dover, 1978. 3) Pasto, D. J., Johnson, C. R., Organic Structure Determination, Prentice-Hall, 1969.

4) Drago, R. S., Physical Methods for Chemists, Surfside Publishing, 1992. 5) Nakanishi, K., Berova, N., Woody, R. W., Circular Dichroism, VCH Publishers, 1994 6) Williams, D. H., Fleming, I., Spectroscopic methods in organic chemistry, McGraw-Hill, 1987.

The Identification of Organic Compounds

Which is why spectroscopic method is better than chemical one ? 1)We need lesser weight of sample.

).s very rapid (i.e takes lesser time ,It) 2

Spectrum ماهية الطيف

مقدمة:

كهرومغناطيسيال الشعاعو matterبين المادة interactionبدراسة التداخل Spectroscopyيهتم علم األطياف

electromagnetic radiation والذي يمتد من أشعة جاما عالية الطاقةhighly energetic إلى موجات الراديو المنخفضة

مرورا باألشعة السينية وأشعة المايكروويف واألشعة فوق البنفسجية والمرئية وتحت very low energeticالطاقة جدا

. الحمراء

فإنها تعني: قياس هذه التداخالت بين المادة والشعاع وصفيا عن طريق Spectrometryأما القياسات المطيافية

التعرف على التراكيب الكيميائية لهذه المواد أو كميا عن طريق قياس تراكيز هذه المواد.

Physical Properties

Melting Point

Boiling Point

Density

Solubility

Refractive Index

Chemical Tests

Hydrocarbons

Alkanes

Alkenes

Alkynes

Halides

Alcohols

Aldehydes

Ketones

Spectroscopy

Mass

(Molecular Weight)

Ultraviolet/Visual

(Conjugation, Carbonyl)

Infrared

Functional Groups

NMR

(Number, Type, Location of protons)

Gas Chromatography

(Identity, Mole %)

http://ar.wikipedia.org/wiki/%D8%A5%D8%B4%D8%B9%D8%A7%D8%B9http://ar.wikipedia.org/wiki/%D8%A5%D8%B4%D8%B9%D8%A7%D8%B9http://ar.wikipedia.org/wiki/%D8%A5%D8%B4%D8%B9%D8%A7%D8%B9_%D9%83%D9%87%D8%B1%D9%88%D9%85%D8%BA%D9%86%D8%A7%D8%B7%D9%8A%D8%B3%D9%8Ahttp://ar.wikipedia.org/wiki/%D8%A5%D8%B4%D8%B9%D8%A7%D8%B9_%D9%83%D9%87%D8%B1%D9%88%D9%85%D8%BA%D9%86%D8%A7%D8%B7%D9%8A%D8%B3%D9%8A

أو راسم طيفي Spectrometers بالمطيافيات أو أجهزة مقياس الطيفوأما األجهزة التي تقوم بهذه القياسات تدعى

Spectrograph بمخطط طيفين المادة والشعاع . ويشار الى مخطط التداخل بي spectrogram طيفأو spectrum .

بالكونوتشكل بذلك ما يعرف ، volumeويشغل حيز من الفراغ ، أي له حجم massهي كل شيء له كتلة -والمادة:

atom، والذرة ط كميائيةبرواب الذراتفهي تتكون من تجمع chemical elements العناصر الكيميائيةالملموس. أما

neutronsات النيوترون)جسيمات موجبة الشحنة( و protonsات البروتونتحتوي علي عدد من nucleusتتكون من نواة

)جسيمات سالبة الشحنة( وأن تلك الجسيمات هي electronsات إلكترون)جسيمات متعادلة دون شحنة( ويدور حولها

حيث تكون صلبة أو سائلة أو غازية. phasesوتتعدد صور وحاالت المادة الجسيمات االساسية المكونة للمادة ،

. s the study of the interaction between radiant energy and the matter ,What is spectroscopy? It

(Monochromatic light )يكون على شكل ضوء احادي الموجه الضوء

Electro magnetic radiation :- It is the radiation energy transmitted through the speace in the form of wave .

كمات من الطاقه تنتقل في الفراغ بشكل موجي -الضوء :

Electric and magnetic field components of

plane polarized light

* Light travels in z-direction

* Electric and magnetic fields travel at 90° to each other at speed of light in particular medium

in a vacuum) 1-cm s 10c (= 3 × 10

* Electromagnetic radiation :- of which visible light has the properties of both particles and waves.

* The range of photon energy is called the electro magnetic spectrum

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Characterization of Radiation

E = energy , h = plank constant , υ = frequency , λ = wave length

s the distance between the crest in the wave to the crest in the next ,It -:Wave length

.s the number of the complete cycle in the second ,It -: Frequency

Because we have different wave lengths and different frequencies therefore will have

Different energy.

Wavelength and Energy Units

Wavelength :-

)(millimicrons m 7=10 4 nm = 10 7Å = 10 8cm = 10 1

N.B. 1 nm = 1 m (old unit)

Energy :-

of particles 1-= 2.858 cal mol 1-cm 1

1-erg molecule 1610 1.986= 1-eV molecule 4-10 1.24=

) (Å ) 1-E (kcal mol 510 2.858=

)(nm/510 ) = 1.19 1-E(kJ mol

297 nm = 400 kJ

Beer’s Law

= Intensity of incident light oI

I = Intensity of transmitted light

= molar extinction coefficient

l = path length of cell

c = concentration of sampl

υhcλ

hchυ)moleculeΔE(erg

λ(cm)

1υ

λ(cm)

)secc(cm)υ(sec

molecule

sec erg106.626h

E

hcλor

λ

hcE

energyor υ,υλ,

1

11-

27

lcAI

I010log

Absorption Spectroscopy

Energy States

Energy absorption by transparent materials in any portion of the electromagnetic spectrum

causes atoms or molecules to pass from a state of low energy (ground state) to a state of

higher energy (excited state).

:of Energy States There are 3 types

i)Electronc ii) Vibrational iii) Spin

-: Types of Spectrometry

The four most important types of spectrometry that organic chemists

routinely use are:

Electronic Energy States –Ultraviolet Spectroscopy (UV) )1

Use –Conjugated Molecules; Carbonyl Group, Nitro Group

rgy StatesVibrational Ene –Infrared Spectroscopy (IR) )2

Use – Functional Groups; Compound Structure

StatesNuclear Spin –Nuclear Magnetic Resonance (NMR) )3 Use – The number, type, and relative position of protons (Hydrogen nuclei) and Carbon-13 nuclei

Bombardment Energy Electron-Hi –Mass Spectrometry (MS) )4

Use – Molecular Weight, Presence of Nitrogen, Halogens

Each of these methods provides unique information about organic molecular structure because each monitors the

response of an organic molecule to a different type of energy input. In MS ( do not use spectrometry), a molecule is

bombarded with a beam of high energy electrons, in NMR it is irradiated with radio waves, in IR it is subjected to

heat energy, while in UV-Vis spectrometry the molecule is placed in a beam of ultraviolet or visible light

:Spectroscopy Types

UV and Visible Spectroscopy

* Ultraviolet: 190~400nm * Red: 620 - 780 nm

* Violet: 400 - 420 nm * Orange: 585 - 620 nm

* Indigo: 420 - 440 nm * Yellow: 570 - 585 nm

* Blue: 440 - 490 nm * Green: 490 - 570 nm

)200 nm -rays ( 100 -or soft X Vacuum UV *

absorb strongly in this region 2and CO 2, O Quartz*

lamp 2350 nm) Source is D –purge good down to 180 nm Quartz region (200 2N

800 nm) Source is tungsten lamp –( 350 Visible region*

Visible light occupies a very small region of electro magnetic spectrum .

)(red 7-nm (violet) to 8x10 7-It is characterize by wave length of 4x10

light-All organic compounds absorb UV

C-C and C-H bonds; isolated functional groups like C=C absorb in vacuum UV; therefore not

readily accessible

* In structure determination : UV-VIS spectroscopy is used to detect the presence of

chromophores like dienes, aromatics, polyenes, and conjugated ketones, etc

and polyunsaturated compounds NH(R)C=O-O(R)C=O, -C=O, 2R Important chromophores are*

المحاضره الثانيه

Spectral measurement

*usually dissolve 1 mg in up to 100 mL of solvent for samples of 100-200 D molecular weight *data usually presented as A vs (nm)

to make spectrum independent of sample 10or log axis is usually transformed to y for publication,*concentration

Electronic transitions

A phenomenon of interaction of molecules with ultraviolet and visible lights. Absorption of photon

results in electronic transition of a molecule, and electrons are promoted from ground state to higher

electronic states.

There are three types of electronic transition which can be considered;

Transitions involving p, s, and n electrons

Transitions involving charge-transfer electrons

Transitions involving d and f electrons

-:Theory electronic transitions

Orbitals involved 5 in electronic transition :- The most probable ∆E transition would appear to involve the an electron from the highest –

occupied molecule orbital (Homo) to the lowest available unfilled orbital (Lumo) , but in

many cases several transition can be observed giving several absorption bands in the

spectrum :-

∆E = h υ = h 𝐶

𝜆

* not all , transition from filled to unfilled orbitals are allowed

ليست كل انتقاالت من اوربيتاالت مملؤة الى غير مملؤة مسموح بها

The symmetry relationship between the two orbitals being important ,where a transition

occurring is " Forbidden " the probability of that transition occurring is low , and correspondingly

the intensity of the assoc rated absorption band is also low

ما يكون االنتقال محضورا فان احتمالية ذلك االنتقال ان تحدث واطئة , وبالتالي فان شدة الحزمة المرتبطة بذلك عند

االنتقال يكون واطئا )ضعيفا(

5

UV Spectroscopy

I. IntroductionC. Observed electronic transitions

6. Here is a graphical representation

Energy

s*

p

s

p*

nAtomic orbitalAtomic orbital

Molecular orbitals

Occupied levels

Unoccupied levels

6

UV Spectroscopy

I. IntroductionC. Observed electronic transitions

7. From the molecular orbital diagram, there are several possible electronic transitions that can occur, each of a different relative energy:

Energy

s*

p

s

p*

n

s

s

p

n

n

s*

p*

p*

s*

p*

alkanes

carbonyls

unsaturated cmpds.

O, N, S, halogens

carbonyls

Modes of electronic excitation

orbital) to (ơlying –the only transition available is the promotion of an electron from a low -:alkanes In**

) ,and requires very*ơ -orbital). This type of transition is called (ơ antibonding *ơhigh energy ( short wave length ultraviolet light around ( 150 nm) .

several transition are available , but the lowest energy transition is the most -:alkenes In simple**

important this is ( 𝜋 - 𝜋 *) transition which is responsible for the absorption band around (170 – 190 nm) in un conjugated system .

bonding electrons –the lowest energy transition involves the non -saturated aliphatic ketones :In **

*) 𝜋 – orbital: this( n* 𝜋 lying –on oxygen one of which can be promoted to the relatively low transition is " forbidden " in the symmetry term and therefore the intensity is low .

UV/VI

S

Vacuum UV

or Far UV

(λ

.these are both allowed*) 𝜋 - ( 𝜋 ) and*ơ -Two other transition available are (n

*) 𝜋 – Transitions and give rise to strong absorption bands, but the energy involved is higher than( n ) and around*ơ -therefore the wave length of the absorption is shorter around (185 nm) for (n ,

(160nm) for ( 𝜋 - 𝜋 *) . ( 𝜋 - 𝜋 *) transitions gives more intense absorption peak.

Q // How can you determine the types of electronic transitions of a given organic compound and depict the its spectrum ?

OH2CH3CH) 1

2CH=CH3CH) 2

CHO2CH3CH) 3

3CH=COH CH2CH3CH) 4

3COH CH 2=CHCH2CH) 5