T H E R A M A N S P E C T R A O F O R G A N I C C O M P O U N D S

Par t I. Methyl, Ethyl, n-Propyl and n-Butyi Alcohols

BY K. KaUSrtNA~ (Department q[ Physics, lndian Institute of Science, Bangalore-12)

Rcccived January 28, 1961

(Communicated by Profi R. S. Krishnan, F.A.SC.)

I. [NTKODUCTION

THE technique of excitation of Raman spectra by the A 2537 radiation from a water-cooled mercury ate has been widely used in the case of crystals both in this laboratory and elsewhere and many interesting results have been obtained. The application of this method to the case of liquids is, however, beset with some practical difficulties, the most important one being that many liquids ate not transparent to the 2, 2537 radiation. In spite of these limitations, Bolla (1934) and Narayanaswamy (1947) employed this technique for investigating the Raman spectra of water, methyl and ethyl alcohols and a couple of hydrocarbons. The spectrograms obtained by Narayanaswamy were partly masked by the presence of a strong fluorescence extending from about ~ 2600 to A 2800 A.U. due to the fused silica Raman tube. In recent years better quality fused silica tubes are available, which do not exhibit any fluorescence in this region. Using such good quality fused silica Wood's tube a systematic investigation of the Raman spectra of liquids, which are transparent to the ultra-violet has been undertakea by the author. As ex- pected, considerably improved and new results were obtained in the case of the first four members of normal aliphatic alcohols, and these results ate presented in this paper.

2. EARLIER WogK

Methyl alcohol is one of the substances, the Raman spectrum of which has been studied by many investigators. A complete bibliography on this subject has bcen given by Narayanaswamy (1947), and also by Halverson (1947). It will not be repeated here. Besides the 'wing', Narayanaswamy reported the existence of 15 Raman lines.

The Raman spectrum of ethyl alcohol has also been the subject of exten- sive study. A complete bibliography on the Raman spectrum of ethyl alcohol is given by Narayanaswamy (1947). Bolla recorded nearly 56 Raman fines in the spectrum of methyl alcohol, while Narayanaswamy reported the existence of only 31 Raman lines.

151

152 K. KmSHNAN

The Raman spectra of n-propyl and n-butyl alcohols were studied by Ganesan and Venkateswaran (1929), Venkateswaran and Bhagavantam (1930), Wood and Collins (1932), Nevgi and Jatkar (1934) and Medard (1934). Trumpy (1930) investigated the Raman spectrum of n-propanol and Kohl- rausch and Koppl (1935) and Sanyal (1950) investigated the Raman spectrum of n-butyl alcohol. Quinan and Weberley (1954) recorded the Raman spectra of all the four alcohols, along with their monodeuterated analogues. The maximum number of Raman lines recorded so far for n-propanol ,,vas 18 and that for n-butanol was 27.

3. EXT'E~Irr162 DETAILS

The methyl alcohol used in the present study was of Merck's guaranteed analytical reagent quality. The liquid was distilled twice be(ore being trans- ferred to the Wood's tube. Ethyl alcohol was prepared from commercial sample as follows: The commercial alcohol was repeatedly distilled, then refluxed with a small quantity of H2SO4 and distilled again. Next, ir was refluxed with pure NaOH (Merck) and distilled. Finally, it was refluxed with CaO and distilled. The final liquid was found to absorb only below 2000 A.U. indicative of the high purity of the sample, n-Propyl and n-butyl alcohols were B.D.H. 'Analar' samples and were distilled over NaOH be(ore use to remove the traces of aldehydes present. Refractive index and specific gravity measurements indicated that the compounds were very pure.

The intense mercury resonance radiation from a water-cooled and magnet- controlled quartz arc was allowed to fall on the liquid, which veas contained in a fused silica Wood's tube. The scattered radiation was condensed on to the slit of a Hilger medium quartz spectrograph. Using a slit width of about 0.04 mm., intense spectrograms were obtained in about 20 to 50 hours with ilford Zenith Astronomical plates. Using the same plates and a slit width of 0.065 mm. intense spectrograms were obtained with about seven days' exposure with a Hilger E-1 quartz spectrograph. In the case of n-propyl alcohol intense pictures could not be obtained because it got decomposed due to prolonged exposure to ultra-violet radiation. The frequency shifts of the Raman lines were evaluated with the help of an iron are comparison spectrum.

3. R~ULTS

The Raman spectra of methyl, ethyl, n-propyl and n-butyl aleohols taken with the Hilger medium quartz spectrograph are reproduced in Figs. 1 (a), 1 (b), 1 (c) and 1 (d) respectively, on Plate IV. The frequency shifts of the stronger lines, as well as some of the intense mercury lines are given in the figures. In Fig. 2 (a), on Plate V, is reproduced a heavily exposed Raman spectrum of methyl alcohol taken with the E-1 quartz spectrograph,

The Raman Spectra of Orgcmic Compounds I 153

while Fig. 2 (b) exhibits a heavily exposed spectrum of ethyl a lcohol taken with the medium instrument. The high frequency shift R a m a n lines are also marked on the figures. The mic ropho tomete r records o f the spectra o f the four alcohols taken with the medium instrument are reproduced in Figs. 3 (a), 3 (b), 4 (a) and 4 (b) respectively, on Plate VI. The frequency shifts together with visual estimates o f intensities ate given in Tables I--IV.

TABLE I Raman spectrum of methyl alcohol

Author Narayana- Plyler Assignment swamy (I.R.)

/ 67 67 . . . .

Wing -) 130 146 . . . .

( 250 234 . . . .

484 (2) 491 . . . .

523 (1) . . . . . .

574 (1) . . . . . .

670 14 b) . . . . u 'r out-of-place bending

864 (3) 872 (3) . . . .

881 (1) . . . . . .

908 (1) . . . . . .

920 (3) 922 (3) 946 ..

1025 (15) 1032 (5) 1033 v5 C-O stretching

1109 (8) 1109 1.4) 1106 v'e CH3 rocking

1159 18) 1150 (3) 1164 us CH3 rocking

1200 (1) .. 1213 ..

1271 (1) .. 1256 ..

1300 to 1370 (2 b) 1346 v s OH in plane deforma tion

1430 (6 b) v' 4.-CH3 asymmetrie bend- lng

K. l~sm,~Ar~

TABLE [ (Contd.)

Author Narayana- swamy

Plyler (I.R.)

Assignment

1450 (16)

1475 (14)

1970 (1)

2074 (2)

2148 (I)

2243 t2)

2305 (2)

2473 (1)

2551 (6)~

2614 (6).1

2683 (2)

2833 (20)

2914 (10)

2946 (18)

2990 (li:))

3200 to 3550

3846 ti)

3934 (2)

4044 (4]~b)

4165 (2)

4275 (2)

1449 (8)

1470 (7)

. .

. .

2585 (2 b)

2833 (10)

2911 (5)

2944 (9)

2989 (5)

3380

�9 e

. � 9

Q @

� 9 1 4 9

1455 m

1479m

2057

2667

2847

2929

2946

2989

�9 .

v3-CH a symmetric bending

v4-CH a asymmetric bend- ing

v I -- v~

2 v 5

v s + v�91

2 P r 6

2v.

v s + vs

O - H . . . . . . . . O

O--H . . . . . . . . O

vx, 2v4

v(-.CH Asymmetric stretch- mg

vl, 2v a

vI-CH Asymmetric stretch- ing

vv O-H stretching (associated)

vi + v5

v i + v,'

P 2 ~ V5

v 2 + ve

vx+ ,,3

The Raman Spectra of Orgcmic Compounds--I

TABLE II

Raman Spectrum of ethyl alcohol

155

Author Bolla Plyler (I.R.)

Assignment

6 3 . . . .

W i n ~ {;20 . . . .

267 t4) 257 (2) 267

359 (1) .. 353

432 (10) 433 (6) 427

525 (4) . . . .

549 (4) . . . .

674 (0) . . . .

775 (6) . . . .

818 (8) 814 (3) 801

843 (1) . . . .

877 (20 b) 883 (60) 877

935 (4) . . . .

1032 (2) 1032 (1) . .

1050 (20 b) 1051 (32) 1067

. . 1073 (1) . .

1090 (16) 1096 (27) . .

1121 (4) 1125 (6) . .

1163 (2) 1160 (2) . .

1276 (10) 1274 (17) 1242

1384 (2) 1386 (5) 1391

�9 ~

�9 ~

vla CHa twisting

v12 C-C-O skeletal bending

. .

v n OH out-of-plane defor- mation

v14 CH2 rocking

2 • C-C-O bending

v5 C-C skeletal stretching

vi5 CHa out-of-plane wagging

q C-O skeletal stretching

vis CH2 twisting

vxv CHa in plane wagging

�9 .

vis CH2 wagging

vi0 OH in plane deformation

3-3

156 K. K~srmAN

TABLE II (contd.)

Author Bolla Plyler (I.R.)

Assignment

1417 (2 b)

. .

1452 (18 b)

1485 (15 b)

1620 (2)

1680 (0 b)

~

~

1974 (i)

2o91 (2) o o

2183 (I)

2250 (2)

2283 (2)

2330 (I)

2439 (l)

2474 (2)

2547 (4)

2598 (4)

2654 (2)

2719 (15 b)

2755 (10)

~

1445 (1)

1455 (46)

1484 (10)

1618(4)

. .

1885 (0)

~921(0)

1969(0)

2065 (1)

2093 (l) 2138(0)

2188(o)

2254(1)

2281 (1)

2327(0)

2431 (1)

2476 (1)

2546(2)

2597 (2)

2647 (1)

2717 (7)

2752 (4)

�9 ~

, ~

1456

. .

. ~

. � 9

, .

2110 . � 9

2le0

�9 ~

�9 .

�9 ~

. o

yo CH bcnding

~

v s CH bending

v7 CH bending

2 • C-C stretching

�9 o

vle + v5

2 v a

2 vxe

v~+ vio

V 5 ~ V 9

vs+ v5

va + 1'1o

V~o + vze

O-H . . . . . . . . 0

t ~

2 ~

The Raman Spectra of Organic Compounds--r~

TABLE I I (Contd.)

I~7

Author Bolla Plyler (I.R.)

Assignment

2829 (16 b) 2835 (5) . .

2880 (20) 2879 (59) 2890

2929 (20) 2929 (100) 2924

2976 (20) 2972 (61) 2977

3232 (6 b) 3240 (3) . .

3390 3359 (10) ..

3628 (2) 3632 (2) ..

3662 (1) 3685 (0) . .

3839 (2) 3852 (2) . .

3948 (1) 3945 (0) . .

4020 (2) 4053 (2) . .

4o92 t i ) . . . .

4237 (2) 4242 (0) . .

v s C--H stretching

V2 ~,

v a C-H stretching

i r

ve O-H stretching--assoeiated molecule

O-H stretching monomer

1,3+ v.

v~q- v5

IS 8 ~ V 4

V 1 31- Ir d

vx+ vxT

vx + vx8

TABLE II l

Raman spectrum of n-propyl alcohol

Author Wood and Plyler Assignment Collins (I.R.)

160 wing

240 (0)

332 (2)

463 (8)

670 (0)

. . . . Wing

. . . . CHa twisting

324 (2) . . Skeletal bending

458 (4) 463 m Skeletal bending

. . . . OH in plane bending

A4

158 K. KRISHNAN

TABLE III (Con:d 0

Author Wood and Collins

Plyler (I.R.)

Assignment

770 (4)

821 (1)

860 (15)

882 (12)

928 (1)

968 (8)

987 (0)

1020 (l)

1054 (12)

1070 (II))

11o1 00)

1133 (4 b)

1172(0)

1204 (0)

1237 (4)

1251 (1)

1273 (8)

1300 (I0)

1342 (2)

1385 (i)

1451 (15)

1467 (I0 b)

1501 (o)

757 (4)

. .

856 (1o)

. � 9

967 C4)

o ~

~

i049 (5)

1064 (6)

i00 (6)

. .

! 268 (4)

1296 (6)

. o

~ 1 7 6

1451 (10)

~

758 w

. .

o � 9

898 m

~

971 s

. ~

1013 w

1047 m

1066 v.s.

�9 ,

1218 s

. ~

1276 v.w.

o *

. w

1393 s

1464 m

CH2 rocking

C-C skeletal stretching

C-C skeletal stretching

CH3 out-of-plane wagging

C-O skeletal stretehing

CHz twisting

CH3 in plane wagging

CHz twisting

CH2 wagging

CHz wagging

882 + 463

OH in plane bending

CH bending

CH bending

1054 + 463

The Raman Speetra of Organic Compounds--I

TAnLE III (Contd.)

159

Author Wood and Plyler Assignment Collins ti .R0

1640 (0) . . . . 130~ q- 332

2110 (0) . . . . 1054 • 2j

2197 (0) . . . . 1300 q- 882

2240 (0) . . . . 1101 q- 1133

2338 (0) . . . . 1451 q- 882

2460 (0) . . . . 1133 -l- 1300

2 5 5 0 (2 b) . . . . o - H . . . . . . o

2595 (4) . . . . . .

2677 (8) 2663 (1) . . . .

2738 (12) 2731 (2) .. ,,

2876 (23) 2873 (15) 2892 m CH stretehing

2915 (18) 2905 (I0) 2929 s ,,

2942 (18) 2931 (I0) 2946 s ,,

2970 (18) 2963 (10) 2978 s ,,

3232 (4 b) . . . . 2915 q- 332

3380 (Band max.) . . . . O-H stretching--associated

3630 (2) . . . . O-H stretching--monomer

3685 (1) . . . . 2915 q- 770

4. DISCUSSlON

Methyl alcohoL---Thirty-five R.aman lines have been observed in the spectrum of methyl alcohol of which ." 0 have been recorded for the first time. The frequency shifts observed by Narayanaswamy are given in column 2 of Table I. In the third column are given the positions of prominent infra-red absorption maxima observed by Plyler (1932). The 'wing' accompanying

160 K. Klt tsm~~

TALLE IV

Raman spectrum of n-propyl alcohol

Author Wood and

Collins

Quinan and Weberley

(I.R.) Assignment

O- 2OO

272 (1)

349 (5)

398 (12)

450 (4)

485 (4)

515 (4)

670 (0)

748 (2)

807 (8)

825 (15)

844 t6)

882 (8)

903 (8)

945 (8)

963 (8)

971 (8)

992 (1)

1025 C8)

1057 (8)

I072 (10)

�9 ~

350 (2) ]

394 (6)~

448 (2).)

483 (2)

514 (2)

805 (4)

825 (8)

845 (3)

877 (4)

901 (4)

944 (4)

963 (4)

�9 ~

I025 (4)

1051 (4)

1067 (4)

~ 1 7 6

, ~

698

738

799

853

954

997

1021"~

1057~

1070J

Wing

CHs twisting

C-C-C-C-O skeletal bending

�9 ~

O--H out-of-plane bending

CH~ rocking

CHs Wagging

C-C Stretching

C-O skeletal stretching

The Raman Spectra.of Orgnnic Compounds I

TABLE IV (Contd.)

161

Author Wood Quinan and

and Weberley Assignment Collins (I.R.)

1110

1136

1222

1256

1304

1343

1369

1382

1433

1448

1465

1481

1896

2196

2274

2332

2428

2485

2523

2593

2667

269O

(IO)

(3)

(4)

(6)

(12)

O)

(1)

(1)

05)

05)

05)

(12 b)

tO)

(2)

(1)

(0)

(2)

(I)

(1)

(4)

(4)

~4)

I 104.(6)

1135 (1)

o o

1296 (l) -

�9 ,

1447 (lO)

�9 ,

1476 (4)

2660 (I)

�9 �9

!1 �9 ~

1394

't

CH2 twisting

CH.. wagging

O--H in plane bending

C-H betlding

1072 --' 825

1304 -+- 882

1448 + 825

1448 ~ 882

1304 + 1110

1222 + 1256

1448 + 1072

O-H . . . . . . . . O

A~5

162 K. Ieausrm~

T~d3LE IV (Contd.)

Author Wood Quinan and

and Weberley Collins (I.R.)

Assignment

2720 (8) 273~. 1 ~'~y ..

2744 (8) . . . .

2871 (20) 2865 (10) 2853 ]

I 2906 (20) 2903 (10) 2893 2926 ~

I 2938 (201 2932 (10) 2949 [

J 2965 (20) 2963 (15) 2973

3221 (6 b) . . . .

3390 . . . .

36413 (2) . . . .

3685 (1) .. 3682

O-H . . . . . . . . O

C-H stretching

2965 + 272

O-H st retch ing--assoeiated

O-H stretchinghmonomer

2938 + 748

the Rayleigh line is found to extend up to 250 wave numbers. It exhibits two maxima, at about 67 and 130 cm. -~ which are in agreement with the values given by Narayanaswamy. Because of the fluorescence of the eon- tainer, Narayanaswamy was able to record only the very intense lines in the high-frequency shift region. The O-H stretching band extends from about 3200 to 3550 cm. -~ with a maximum at about 3370 cm. -x The appear- ance of a series of weak and broad lines in the region 3800 to 4200 cm. -x is a new feature of the spectrum of met~y�91 alcohol (Fig. 2 a).

F rom theoretical considerations it can be shown that methy! alcohol molecule should exhibii twelve fundamental vibrational frequencies, eight of them (1,1 to us) symmetric with respect to the C - O - H plane, anfl four (v2', v4' , v 6' and vs') antisymmetric with rcspect to the above plane. Fre- quencies of the first three antisymmetric vibrations may be expected to lie close to those of three symmetric vibrations.

AII the twelve frequeneies should be present in the Raman speetrum of methyl alcohol. They havc been identified and their assignments aro

The Raman Spectra Of Organic Compounds--I 163

indieated in column 4 of Table [. As frequency shift of the overtone of vA, i.e., 2v 4 is nearly equal to that of vi, one should expeet Fermi resonance splitting. The two Ramau lines arising therefrom ate 2833 and 2946 cm. -1 They have been assigned as v I and 2v4.

The assignments given in Table 1 are in general agrecment with those given by Margottiu-Mac[ou 0960) for methyl alcohol vapour. One CHs rocking frequency at about 1070 cm. -1 in the vapour might have shifted to 1109 cm. -l in the liquid due to association. The existence of two Raman lines at 1056 and 1171 cm. -j. observed by Halford, Anderson and Kissin (1937) in the spectrum of methyl alcohol has not been eonfirmed and hence assignments given by Herzberg (1945) based on these Raman lines may have to be revised.

The comparatively fainter lines appearing in the region 1900-2500 cm. -1 and 3800-4300 cm. -1 have been explained as combinations and the respec- tive assignments have been indicated in Table I. The Raman line at about 1970 cm. -1 may be assigned as a differential, i.e., v~-v 5 and the corresponding summational appears with moderate intensity at 4044 cm. -~

There ate 3 Raman lines betwecn 2500 and 2800 cm. -1, two of which are too intense to be explained as summation frequencies, and the third at 2683 cm. -~ does not seem to correspond to any summational frequency. These lines are assigned to the O-H . . . . . . O vibrations, due to hydrogen bonding between the hydroxyl groups of associated methyl alcohol moleeules in the liquid state.

Van Thiel et al. (1957) have shown that methyl alcohol can form cyclic and open-chain dimers and higher polymers. The maxima observed in the 'wing' at about 67 and 130 cm. -a might correspond to the rotational oscillations of the CH3OH units in the dimers and polymers about the hydrogen bond.

Th•re are quite a few weak Raman lines, namely, 484, 523, 574, 964, 881,908, 920, 1200 and 1271 cm. -1, which could not have been assigned either to any of the fundamental vibrations of the CH3OH molecule or to their differentials. They may have to be attributed to the internal oscillations modified under the influence of association.

Ethyl alcohol.--Forty-nine Raman lines have been recorded for this liquid (Table II). The frequeucy shifts reported by Bolla ate given in column 2. Though Narayanaswamy (1947) was able to record a few faint lines br I000 cm. -~ many of the fainter lines in the region 2000-4500 cm. -1 wcre not rr by hito. The author was unable to r the existence

164 K. KRISHNAN

of some of the fainter lines reported by Bolla. The prominent infra-red absorption maxima reported by Plyler (1952) are given in colunm 3. The O-H band extends from 3200-3550 cm. -1 exhibiting two maxima at about 3232 and 3390 cm. -1 The 'wing' in ethyl alcohol extends up to 200 cm. -x and exhibits two maxima at about 63 and 120cm. -1

The C2H~OH molecule should possess 21 fundamental modes of vibra- tion, all of which are expected to appear in the Raman effect. The assign- ments of the observed Raman lines to the vibrational frequencies marked arbitrarily as v 1 to v~ s are indicated in column 4 of Table II. These a.re done by comparing the observed intensities of the Raman lines and making use of the infla-red data of Plyler (1952), and Barrow (1952) on ethyl alcohol and Sheppard (1949) on ethyl halides.

As in the case of methyl alcohol, the fainter lines between 1900-2500 cm. -x and 3800-4300 cm. -1 are assigned to combination frequencies, and the stronger lines between 2500 and 2800 cm. -x to O-H . . . . . . O vibrations. The 'wing' structure could once again be attributed to the rotatory oscillations of the C2HsOH units in the associated groups about the hydrogen bond.

An interesting feature of the Raman spectrum of ethyl alcohol is the presence of two lines in the region of the free O-H stretching vibration, i.e., 3600-3700 cm. -1 The higher frequency line at 3662 cm. -x is the weaker of the two, and can be attributed to a combination frequency. Then the stronger line at 3628 cm. -1 can be explained as due to the O-H stretching vibration of the siugle or unassociated molecule.

In this case also, there are a few faint lines of low-frequency shifts, which correspond neither to the fundamental vibrations of the molecule nor to combinations. These lines might owe their o:igin to the internal oscillations of the associated m01ecule. The fairly intense line at 818 cm. -1 may be ascribed to the C-C skeletal stretching oscillations the frequency of which has been lowered due to a%ociation.

n-Propyl alcohol.--As mentioned earlier, the spectrum of this compound is very weak because of the fact that the sample got decomposed due to over-exposure. Forty-five Raman lines have been recorded and are given in Table [[I. The frequency shifts reported by Wood and Collins (1932) are given in column 2. About 27 Raman lines have been recorded for the first time. The infra-red data of Plyler (1952) are given in column 3. The 'wing' accompanying the Rayleigh line is very faint and extends up to 160cm. -x and does not seem to show any maximum. The O-H band in this case extends from about 3200-3500 cm. -1 exhibiting two maxima at about 3232 and 3380 cm. -1 The important Raman lines have been assigned

The Raman Spectra of Organic Compounds--I 165

to the fundamental modes of vibration of the n-propyl alcohol molecule as indicated in column 4 of Table [II. Simpson and Sheppard (1955) have shown that the skeletal frequencies of alcohols and amines can be identified by comparison with the corresponding fluoride or the next higher hydro- carbon in the series. Thus, considering n-propyl alcohol molecule, it is seen that it has approximately the same molecular weight and contains the same number of CHe groups as n-butane-CHsCH2. CHe, CH3. Hence, by a judicious comparison of the data concerning this molecule, the funda- mental vibrational frequencies of n-propyl alcohol can be identified with reasonable accuracy. But n-butane is known to existas a mixture of rota- tional isomers in the liquid state. This difficulty is overcome by using the data for only one form of n-butane, in this case, trans-n-butane. The vibra- tional artalysis for the latter molecule has been made by Szasz, Sheppard and Simpson (1948), and these ate used in assigning the fundamental frequencies of n-propyl alcohol.

The fainter Raman lines appearing in the region 2000-2500 cm. -1 are explained as combinations and those between 2500 and 2800 cm. -1 as due to O-H . . . . . . O vibrations. As in the case of ethyl alcohol, here also there ate two lines in the region 3600-3700 cm. -1 The stronger of the two, i.e., 3630 cm. -1 is assigned to the O-H stretching vibration of the unassociated molecule and the other fainter lirte at 3685 cm. -1 is explained as a combina- tion frequency.

n-Butyl alcohoL--Fifty-one Raman lines have been recorded in the spectrum of n-butyl alcohol and are given in column 1 of Table IV. 24 of them are recorded for the first time. In columns 2 and 3 are givert the fre- quency shifts reported by Wood and Collins (1932) and infra-red absorp- tion maxima reported by Quinan and Weberley (1959) respectively. The O-H band extends from 3200-3550 cm. -x exhibiting two maxima at about 3221 and 3390 cm. -~ There is a weak fluorescence superposed on this band. The 'wing' accompanying the Rayleigh lirte extends up to about 200 cm. -1 and does not seem to show any structure.

The assignments of the important Raman lines observed ate indicated in column 4 of Table IV. These are made by ah extension of the assign- ments for n-propyl alcohol, and also by comparing the results obtained for n-butyl alcohol, with those of 7z-pentane. For the above purpose, only the data on the gauche form of n-pentane given by Tchamler (1954) are used.

There a r e a series of 8 sharp and intertse Raman lines with the frequency shifts varying from 807 cm. -~ to 971 cm.-L The CH~ rocking, C-C and (?Ha wagging modes of oscillations are expected to give intense Raman fines

166 K. KRm~NaN

in this region. There should be threc different types of C-C oseillations in the butyl alcohol giving rise to three different Raman lines. One might expect further splitting of some of these modes due to the existence of the phenomenon of rotational isomerism (Berthelot, 1950 a_ad Brown, Simpson and Sheppard, 1950). In view of the larger number of lines of nearly equal intensity appearirtg in this region, it is difficult to assign a particular Raman line to a particular mode. They have theretbre been clubbed together in Table IV.

The faint lines appearing in the region 1850-2000 cm. -1 have been assigned as eombinations and those between 2500 and 2800 cm. -1 as O-H . . . . . . O frequeneies. In this spectrum also there ate two Raman lines between 3600 and 3700 era. -1, the lower frequency one being assigned as the O-H stretching frequency of the single molecule and the higher frequency one a s a combination.

S ~ Y

The Raman speetra of methyl alcohol, ethyl alcohol, n-propyl alcohol and n-butyl alcohol have been recorded using ,~ 2537 excitation. 35, 49, 45 and 51 Raman lines respectively have been identiŸ in the spectra of these alcohols, in addition to the rotational 'wings'. In each case, a large number of additional lines have been recorded. The existence of Raman lines with frequency shifts greater than 3800 cm. -1, tirst reported by Bolla in the spectrum of ethyl alcohol, has been cortfirmed. Similar high-fre- quency shift Raman lines have also been recorded in the spectrum of methyl alcohol. They have been assigned as eombinations. Proper assignments have beca given for the prominent Raman lines appearing in the spectra of these alcohols.

ACKNOWLEDGEMENTS

The author is grateful to Prof. R. S. Krishnan for suggesting the prob- lem and for valuable discussions. The author's thanks are also due to Dr. P. S. Narayanan for useful suggestions.

1. Barrow, G.B. ..

2. Berthelot, C. ..

3. Bolla, (L ..

4. Brown, J. K., Sheppard, N. and Simpson, D. M.

5. Ganesan, A. S. and Vr S.

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K. Krishnan Proc. lnd. Acad. Sci., A, Vol. LIlI, PI. IV

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K. Krishnan Proc. lnd. ,4cad. Sci., A, Vol. LIII, PI. V

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K. Krishnan Proc. In& Acad. $ci., A, VoL LIII, PL VI

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FIG. 3. (a) Microphotometer reco~d of the Raman spectrum of rnethyl alcohol. (b) . . . . . . ethyl alcohol.

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Fxo. 4. (a) Microphotometer record of the Raman spectrttrn of n-propyl alcohol. (b) . . . . . . n-butyl alcohol.