V I B R A T I O N A L S P E C T R A A N D N O R M A L

V I B R A T I O N S O F A C E T A N I L I D E A N D N - D E U T E R A T E D A C E T A N I L I D E

Bv V. VENKATA CHALAPATHI AND K. VENKATA RAMIAH

(Department of Physh's, College of Sciencc, OsmaMa University, Hyderabad-7)

Received Novembcr 23, 1967

(Communicatod by Dr. N. A. Narasimham. F.A.SC.)

ABSTRACT

The Raman and infra-red spectra of acetanilide and N-methylaceta- mide and of thcir N-deuterated corrŸ have been recorded. The vibrational frequencies of acetanilide have been assigned and the nature of the Amide 1, II and IlI bands in acetanilide and N-methylacetamide has been investigated by the study of the changes in the frequencies of these bands in the spectra of their deuterated compounds. Acetanilide and deuterated acetanilide molecules have been subjected to normal co-ordinate treatment and the mixing up of the skeletal frequencies arising out of the in-plane vibrations has becn determined. These results indicate that as in secondary amides, the amide II and amide [II bands in acetanilide are due to the combined contribution of �91 (NH) and v(C--N) vibrations, but the contribution of v(C--N) to the amide II band is less in acetanilide and deuterated acetanilide than in cases of N-methylacetamide and deuterated N-methylacetamide.

INTRODUCTION

THE planarity o f - - C O N H - g r o u p in substituted amides has beel~ well establishcd from infi'a-red, Raman and Ultra violet absorption spcctra, 1-~ dipole momcnt measurcments and eleetron diffraction studies? Suzuki e t a l ? invcstigatcd the near infra red absorption spectra and measurcd the dipole moments of a number of anilides in solution of carbon tetrachloridc at various comentrat ions and showcd that acetanilidc has a .:raT.s-structure with ' O ' and ' H ' atoms in ~'ram-position about the C - N bond. The infra-red spectre of acetanilide and its deuterated specics werc studied by Abbott et al. ~o and Soichi Hyashi, ~~. ~~ using polarised radiation. Earlier infra-red studies of acetanilide hav e been included in the papers by Crooks, TM

184

Vibrational Spectra, Vibratiom o f Acetanilide & N-Deuterated Acetanilide 185

Mann and Thompson, at Banford etal. .£ and Gierer. a~ Thatte etal . 1• recorded the Raman spectra of a f~w arr, ides and anilides. There appears to be no mcntion in earlier literature about the assignmcnt of all the fundamental frequcncies of acetavilid~. The: infra-red and Raman spectra of acetanilide and N-mcthylacctamidc and of ff, cir N-dcuterated spccies have been recorded with a vicw to (i) assign all the fundamental frequencies of acetanilide (ii) compare the frequencics of 0mide I, anaide II and amide III bands in N-methylacetamide and acctanilidc and in their deutcrattd compounds and (iii) study the nature of the amide I, amide Ii and amide IIl bands by subjecting acetanilide to normal co-ordinate treatment and comparing these results with those of 1N-methylacetamide.

EXPERIMENTAL

The infra-red spectra of N-methylacetamide and N-deuterated N-methyl- acetamide and of them in solutio~s of chloroform in the region 3,500 cm. -1 to 400cm. -~ were recorded with Perkin-Elmer Modcl 21 and Model 337 spectrophotometers. The infra-rcd s p,(ct:a of aceta~ilidc and N-deu- terated acetanilide and of thcm in solution of chloroform were recorded in the region of 3,~00 cm. ---J to 2,400 cm.-~ by Perkin-Elmer Model 221 speetrophotometer with NaCI optics, in the region of 1,700 cm. -1 to 1,200 cm. -1 and 4130 cm. -~ to 250 cm. -1 by Perkin-Elmer Model 21 spectrophoto- meter with NaCI and CsBr Prisms respectivdy ar.d in the regicn 1,3130 cm: -~ to 400cm. -~ by Perkin-EImer Model 337 grating spectrophotometer. The Raman spectrum of acetanilide was recorded in sol~tion of methanol using Hilger Raman source unit and Fucss glass speetrograph. ~ 4358 was used as exeiting radiation.

RESULTS

The infla red and Raman frequencies of acetanilide and their assign- ments ate given in Tablc I and some of the frequencies of N-methyla(etamide and acetanilide and thcir deuterated compounds are given in Tables II and III.

The infra-rcd spectra of N-methylacetamide and acetardlide and of their deuterated species are shown in } igs 1-4 and the Raman spectrum of acetanilide in methanol is given in Fig. 5.

The spectra of the deuterated N-methylacetamide and acetanilide show weak peaks in the N-H stretching and bending regions indicating that only about 70.Ÿ of these eompounds could be converted to deuterated substances.

186 V. VENKATA CHALAPATHI AND K . VENKATA RAMIAH

TABLE I

Infla-red and Raman spectra of acetanilide (Frequeneies in era. -a)

Infra-red

Pure anilide KBr Anilide in solution pellet and mull of CHCIa

Raman

Anilide in solution of CHaOH

Assignment

[ 2 3 4

~ 1 7 6

~ 1 7 6

3127" (8)

3o4~'(8)

3440 (m) 3305"ivs) 3q20 (m) 3270 (w) :~,2,'o (w) 3205 (w) 3205 (w) 3)45 (w) 3145 (w) 3090 (Sh) 308() (~h) 3065 (w) 3065 (w) 3030 (w, 3010 (s) 2980 (vw) .. 2930 (~w) 2860 (vw) 2860" ivw) 2810 (vw) 2810 (vw) 1950 (w) 1940 (w)

1780 (vw) 1658" �91 1686 (vs) 1598 (si 1598 (a) 1549 (s) 1510 (s) 1500 (m) 1497 (m) ]428 (s) 1436 (s) 1361 (m) 1366 (m) 1316 (s) 1305 (s) 1258 (s) 1240 (s) 1170 (w) 1165 (w) 1074 (w) 1074 (w) 1030 (m) 1025 (m)

1017 (m) 1000" im) 1005 (m) 955 (m) 95,5 (m) 900 ( m) 892 (m) 853 (w) 842 (w) 843" iw) 745 (vs) 685 (m) 682 is) 650 (m) .. 600 (m) .. 528 (m) .. 505 (m) .. 369 (m) .. 34~ (s) ..

, . . *

v (N- -H) free v (N--H) bonded 1673 + 159~ 1658 + 1549 1598 + 1549 v (C--H) A1

do. ~

202~" (2) 2s36 (t)

. o

, .

167~" (3) 1603 (5) 1550 (1) 1507 (1)

1377" (1) 1325 (5) 1269 (3) 1179 (1)

. .

lO2.;" (~) 1001 (4)

. .

850" 759 (2) 665 (3)

) ~

~

~

358" (1) 279 (1)

vas (Cti3) 1549 + 1428 vs (CH3) 1428 + 1428 1549 + 1258 1258 + 685 1030 + 745

(c=o) Ring A1 8 (N- -H) in-p!ane Ring B1 8a8 (CHa) in-plane �91 (CIta) in-plane

v (C--N) �91 (eH) .% 8 (CH) B, r CCH) Out-of,plane v (N-- CeHs) Ring A1 r (CH3) in-plane 8 (CH) A2 505 + 345 v (C--Ctfa) 8 (CH) B2

do ( O = C - - N )

8 ( N - - H ) � 9 1 Ax

(C- -C- -C) B~ �91 ( c = o ) • r (C--CHe) 8 (C--N--C6H~) in-plane

The absorption bands, arising out of the N - H and N - D stretching and bending vibrations and the amide I, the amide II and the amide HI bands in N-methylacetamide and acetanilide and their deuterated compounds ate indicated in the figures by arrow marks,

Vibrational Spectra, Vibrations of AcetanilMe & N-Deuterated Acetandides 187

TABLE II

Some of the vibrational frequencies of N-methylacetamide and deuterated N.methylacetamide

N-methy lace taan ide C H 3 . C O . N H C H ~

- Frequenc ies (in c m - 1 ) of M o d e

of ] P a r e In s o l a t i o n of v ib ra t ioa I an i l i de C H C I a

/

v ( N - - H ) . . 33;hb 3470

v ( C = ( 3 ) Amide I . . 1647 1~i91

a ( N - - H ) A m i d e I I . . 1:-)58 14~6

v ( C - - N ) A m i d e I I I . . 13f)(J 1250

v ( C - - C l t a ) . , 881 865

6 (? �91 • . , 70., . .

D e u t e r a t c d N - m e t h y i a c e t a m i d e C t ic . C o . N D C [ I a

F requenc ies ( i n cm. - z ) of

P u r e In so lu t ion o f ani l ide C 11CI

M o d e of

v ib r a t i on

v ( N - - I ) )

v (C :- O)

�91 ( N - - I ) )

v ( C - - N )

v ( C - - C l i p ]

2475 2564

1639 1653

1 479 1479

1120 1120

871 862

5:!0 . .

TABLE III

Some of the vibrational frequencies of acetanilide and deuterated acetanilide

Acetalf i l ide C I I . C O . N t I . CsH~ Deu te ra t ed ace tan i | ide C t I 3 C O . N D . C � 9 1

F requenc i e s (in cm. -1 } of F requenc ies ( in cm. - 1 ) of Modc

of vi b ra t ion

. ( N - - I t )

v ( C = O ) A m i d e i . .

(3 ( N - - t i ) A m i d e I i . .

v ( ( ' ~ N ) Amide I l i . .

,, (C--CH3) . .

8 ( N - - I I ) a. . .

Pu re In so!ut ion an i l tde of C H C I 3

3505 :~440

1658 1681]

1549 1510

1258 1240

84? �9 �9

600 �9 �9

'. ode of

vi b ra t ion

,, (N--O)

v ( C = O )

�91 ( N - - I ) )

(C .N)

v (C ( I { , O

5 ( . \ ' . . i ) ) •

P u r e I n s o h t i o n ani]ifie of CHCI, ,

2425 256:2

16-10 1660

74~0 1410

lO~u 1080

8"2O . .

. ) 4 . ' ~ . .

DISCUSSION

The rcsuhs in Tablc.~ 1I and 1II indicatc that the N - H and the C = O stretcbing frequencics in N-Methylacetamide and acetanilidc ha'v;e higher

alues in solutions of chloroform than in case of the pure compounds and

188

O4O

V. VENKATA CHALAFATHI AND K . VENKATA RAMIAH

F R E Q U E N C Y ( C M - I ) 160O 1400 0.0~ I�91

~ 0-2 , .; -, .,., "" ': :'

~o, \ ! : ~/v ~ ii

06 i l j ::

5500 3000 2500 FREQUENCY (CM "l)

0.I

i ,SI

.:~ '~ :.

FJG. 1. lnfra-rcd sp~ctra of zt~etanilide--So!id l ineand N-dcutcrated acetanilide~Brokc:~ line. (3,500cm. -~ to 2,400cm. -~ rccorded by KBr disc techniquc; 1700cm. -~ lo 1,200crn." recorded by lntlll tcchniquc).

FREGUENCY (CM -3) FREO, UENCY (CM "l)

4 0 0 0 3 0 0 0 2500 1800 1600 t400 I i I I i I

o.o F o.o~

I I i

~" ~ ~ ~

<" F ~ ,,, ; '~ : < 0-4, , ,J , , o.4

I t ,". ,,~ : i

~ V ', o:~ o.~ :,/ ~ I'0 I'5 ~- ,

t t ' "t I i/ ~ /

. , P i �9

FrG. 2. Infra-rcd spectn~ of N-mzthylacctamidc So;id!ine z:ndN-dctl ten, tc~! N - n c t l y l acetainid.z --Broken lino (Sp:ctra rccorded with l:quid ii'. the forro of micro film).

the higher frequencies arise out of the stretching vibrations of the free linkages a s a result of breaking up of intermolecular associations in solutions. The N-D stretchinl~ frequencies appear in the region of 2,500 cm. -1 and the frequencies increase by 50 cm. --1 to 60 cm. -1 in solutions. In N-methylacetamŸ the amide II band occurs at 1,558 cm. -1 and the corres- ponding peak in the deuterated N-methylacetamide has ah absorption at

Fibrallonal Spectra, Vibrations of Acetanilide & N-Deuterated Acetaniltde 1 8 9

M I C R O N S

�9 .0 9 . 0 IO.O ii.0 ZO.0 2 5 . 0

FIO. 3.

.10.

,2'0'

.3,O r = ]

. 4 0

.= .~o 1

1.0

i ine.

II

Ii

II

�9 . I I I' I I l

1 2 0 0 I l O 0 l O 0 0 9 0 0 8 0 0 7 0 0 (~DO 5 0 0 4 0 0

F R E Q U E N C Y { c m - I )

[nfra-red spectra of acetanil idz--Solid line and N-deuterated acetaniiide--Brokcn

O.0

*10 l

w-20~

, o t, . 5 0 Ÿ

.60

. 7 0

1.0

FIo. 4.

M I C R O N S 8.0 ~ 0 I 0 . 0 15.0 ~0 ,o I i i I I ~ L _

�91

. . . . . ~ . . . . l . . . . I I - - _ _ I l --' 1 r 3 0 0 1 2 0 0 I t O 0 lOCO 9 0 0 8 0 0 l O O 6 0 0 ~ 0 0 4~K3

F R E Q U E N C Y ( cm - I )

Infra-red spectra of N-methylacetamide--SoIid lino and N-dcuteratr N-methyl ace tamide- -Broken line.

FIG. 6.

C --Q-- N /# ~\.

H 3 C J-i

A. Ac~tanitidc, 13.

0 C 6 Hs \ /

C . . . . N / ',,

M3C D

N-deuterated acetanilidc.

190 V. VENKATA CHALAPATHI AND K. VENKATA RAMIAH

1,479 cm. -1 In acetanilide which is essentially a secondary amide, the amide II band occurs almost at the same frequency as in lq-methylacetamide (at 1,549 cm.-~), but the corresponding absorption of deuterated acetanilide occurs at a lower frequency, being at 1,410cm. -1 The obser~ations in Tab]es II and III indicate that the change in the frequeneies of the amide III band from pure to deuterated compounds in N-methyl acetamide and acetamlide is of sarr, e order while it is considerably different in case of the amide I1 band. The amide ii and, the amide III bands in secondary amides are due to the combined contributions of �91 (N-H) and v ((C-N), vibra- tions, and the difference in the frequencies of the amide II band in deute- rated N-methylacetamide and deuterated acetanilide may therefore be due to the difference in the relative contributions of �91 (N-D) and v(C-N) vibrations in these molecules.

NORMAL CO-ORDINATE TREATMENT

Acetanilide and deuterated acetanilide ate treated as six-body pro- blems taking the CH~ and C~H:, groups as point masses and their structurcs are shr below:

O%. q243 O~C__N/CeH ~ II3c)C--N�9 }IaC / ~D

Acetanilide Deuterated acetanilide

These arc planar molecules with the point group Cs and the tw~lve funda- mental ffequencies ar~, classified into nine in-plane (A') and three out-of- plano (A") v ibrations. The NI -H and N-D stretching frequencies being in the region 3,300cm. --1 and 2,500 cm. -~ and the test below 1,700cm. -~ the former ate scparated flora the latter frequencies. The orthonormalised set of symmetry co-ordinatcs for the in-plane v ibrations of the moleculc ate given in Table IV.

The elements of the F and G matrices havc been oblained in thc usual way and the structure parameters used in thesc calculations, as givtn by Brown et al. ls are given in Table V.

The bond length of N-H bond is taken as lA and all the angles relatcd

:C6Hs to thc g~'oup N / are assumed as 120 o.

\ H

The calculations of normal vibrations of aeetanilide and deuterated acetanilide were made by the method of Wilson. As the CHaCON group is common to N,N-dimethylacetamide m~d acetanilide, the stretching,

Vibrational Spectra, Vibrations of Acetanilide & N-Deuterated Acetanllide 191

TABLE I r

The symmetry co-ordinates

Symmetry eo-ordinates Vibrational mode

R 1 = / ~ a . .

R2----- A b . .

R s - - - - A c . .

R 4 = Ad ..

R5 = l[~v/6 (2Aab-- Aac-- Abc)

R6 = 1/VI2 (Abc-- Aac) ..

R~ = l/V'6 (2Aad-- Ade-- Aae)

R• = l/X/2 (Aae-- �91 ..

C ~ N stretch

C = O stretch

C-2-~ CH3 stretch

N--CeH5 stretch

O = C - - N deformation

C--CHa in-plane rocking

C~Hs--N--C bending

N---H bending

TABLE V

Structure parameters of acetanilide

Bond Bond length Interbond angle

(C=O) 1.23 A ~ O : C - - N =121 ~

(C--N) 1- 33 A ~ N ~ C ~ C H a = 119 ~

(C--CHs) 1-48 A ~ CHs--C =O ---- 120 ~

(N~C6H6) 1" 43 A ~ C----N--H = 120 ~

( N ~ H ) 1" 00 A ~ C6H~~N~H = 120 ~

. . . . C~N--C6H£ = 120 ~

bending and interaction constants related to this group of N, N-dimethyl- acetamidO 9 were transferred to acetanilide. The force constants related to the other bonds, as of N - H and N-C6H5 linkages were taken from similar molecules like N-methylacetamide and from the data given by Wilson, Deeius and Cross. 2o In these calculations, the bond-bond and bond-angle

/L2

192 V. VENKATA CHALAPATHI A N D K . VEiNKA'I'A RAMIAH

interacfion constants were retained and the secular determinant which has the dimensionality of (8 • 8) was expanded by modified Danielewsky's .1 method. A program was written in Fortran language for Model IBM 1,620 digital computer to compute polynomial coeflicients and IBM 1620 goneral program was used to extract the roots of the polynomial. The IBM standard program uses Newton's process for updating the root and once the root is found the polynornial is redueed to a lower degree.

Some of the force constants were adjusted tiU a close fit was obtained between the observed and calculated frequencies. With the final set o f force eonstants, as given in Table VI, the frequencies were caleulated. The observed and calculated frequencies are given in Table VII.

TABLE VI

Force constants of acetanilide

Bond stretcbing f , -- 6.8

Bond-bending

fb -=-9.0

f , - - 4 .0

j.d " 4.6

j ; . = 1 . 8

fbo ~= 0.9

f,, = 0.8

.f,~ = 2"2

f . , = 0 . 7 5

f,~ =.0-31

Bond-bond.. f,~ = 0.8

. . A . = l . 2

.. f ," = 0 . 3

.. fo4 = 0 . 5

Bond-angle.. f0" = 0.6

.. fox~ = 0 . 9

Bond-stretching constants and bond-bond interaction constants arein md./.~ and bending and bond-angle interaction constants are in md./rad.

The force constants used in case of acetanilide, were then transferred to deuterated acetanilide ana the frequencies of deuterated acetanilide were calculated. These are also given in Table VI1. The calculated frequencies of N-deuterated acetanilide are in good agreement with the observed frequencies as seen from Table VII. In these calculations, a

Vibrational Speclra, Vibratkma oj Acetanilide & N-Deuterated Acetandide 193

TABLE Vil

The observed and calculated frequencies

Mode Observed frequencies Calculated Compound of frequencies

vibration Raman Infra-red

Acetanilide

Deuterated

Acetanilide

.. v (C--N) 1269 1258 1254

v (C=O) 1674 1658 1645

v (C--CHz) 850 843 852

v (N--CeH£ 1025 1017 1017

3 (O =C--N) 632 650 630

r (C--CHs) 358 345 350

�91 (C---N--CsHs) 279 .. 276

�91 (N--H) 1550 1549 1554

v (C--N) .. 1080 1068

.. v (C=O) .. 1640 1640

v (C--CHs) .. 820 806

v (N---C6H~) .. 985 999

�91 (O=C--N) .. 645 613

r (C--CHs) .. 345 349

�91 (C--N--CsHo) .. 276 272

�91 (N--D) .. 1410 1450

decrease in f a e has the effect of increasing the frequencies of the amide II and the amide III bands and decreasing that of the amide I band. The bending force constant fae is critical in the sense that a slight alteration in its v alue produces a considerable difference in the frequency of the amide II band. Ah irtcrease in fab has considerable effect on the frequeneies of C - N stretch and O = C - N bending vibrations. The interaction con-

.~tants related to the group CHaCON have high v alues indicating the existence

194 V. VENKATA CHALAPATHI AND K. VENKATA RAMIAH

of considerable coupling between v arious modes of v ibrations. The stretch- ing force constants of C -- ~) and C-N linkages have intermediate values of force constants which ov_e expccts from the idealised double bond and single bond linkages of these atoms. This indicates partial single and double bond charactcr for C = (~ and C - N linkages in acetanilide and this result is similar to that in case of amides.

The elements of the L matrices have been evaluated of homogeneous linear equations represented by

(GF -- E~k) ak = 0

Wherc ak is the kt~~ column of matrix 'a'. is obtained from

N k z Z Ftt" atk at 'k ~ )tk t t t

by using a set

(1) The normalisation factor Nk

(2)

The elements of each column ak of the a ' matrix are multiplied by the corresponding normalisation constant Nk to obtain the L matrix and the relation

LL = G

is verified. Using the expression

FiiLisLis • 100 hs

(3)

the potential energ3, distributions of each normal mode among the various symmetrv co-ordinatcs arc ealculated in cases of acetanilide and N-deute- rated acetanilide and aro given in Tables VIII and IX.

The band at 1,658 cm. -1 (the amide I band) is essentially a C-----O stretch and the contribution of C-N stretching vibration to this frequeney is considerable, being 2~%. In deuterated acetanilide, the frequency of the amide I band decreases only by 18 cm. -1 and the contribution of C = O stretch increases by abcut 15~. The small decrease of the frequency of the amide I band frcm acetanilide te deuterated acetanilide indicates that the contribution of N - H in-plane bending vibration to this mode is negligiblc and this resuit is substantiated by the results of the potential energy distribution in rcgard tc this frequency. Similar results were obtained by Miyazz,wa e t a L 22 in regard to N-methylacetamide.

The frequencies of the amide I1 and the amide II l bands in N-methyl- acetamide and acetanilide and their deuterated species are given in Table X.

Vibrational Spectra, Vibrations of Acetanilide & N-Deuterated Acetanilide 195

TABLE V I I J

Potential energy distribution among different modes of vibrations of acetanilide

Mode Symmetry co-ordinates o f Frequency

vibration Rx R~ Ra R4 R~ R 8 R 7 R 8

v (C--N) .. 1258 26 2 20 1 24 3 7 34

v (C--O) .. 1658 29 51 0 0 1 7 8 4

v ( C - - C H ~ .. 843 5 0 60 32 0 0 0 3

v (N- -CaH ~) ... 1017 15 28 0 13 9 1 31 2

( O = C - - N ) 650 1 0 18 25 29 25 2 1

r (C--CHs) .. 345 5 4 5 17 4 64 0 0

8 (C- -N~C6Hs) 279 8 0 0 6 30 1 53 0

�91 (N- -H) .. 1549 15 15 2 6 9 0 0 56

TABLE ]X

Potential energy distributions among different modes of vibrations of deuterated acetanilide

Mode Symmetry co-ordinates of Frequency

vibration R1 R~ Ra R4 R~ R 6 R 7 Ra

v (C- -N) .. 1080 0 7 17 0 17 0 18 32

v ( C = O ) .. 1640 25 60 0 0 1 8 1 0

v (C--CHs) .. 820 7 1 53 16 1 0 0 20

v (N--CeH~) .. 985 14 22 6 23 2 3 13 19

8 ( O = C - - N ) . �9 645 2 0 12 29 27 22 1 6

r (C--CHs) .. 345 6 5 8 17 5 67 0 0

b (C--N--C6H6) 276 9 0 0 7 30 0 53 1

�91 (N- -D) .. 1410 37 10 7 7 18 0 2 19

196 V. VENKATA CHALAPATHI AND K. VENKATA RAMIAH

TABLE X

Amide Frequencies (in cm. -1) of

Amide II Amide HI band band

N-methylacetamide .. 1558 i 300

Deuterated N-methylacetamide .. 1479 1120

Acetanilide .. 1549 1258

Deuterated acetanilide .. 1410 1080

The normal vibrational analysis of N- methytacetamide bv Miyazawa e t a l .

showed that the amide II and the amide I l I bands in secondaly amides are due to the combined contribution of £ ( N - H ) a n d v ( C N ) v i b r a - tions. In N-methylacetamide the potential energy distribution calculations by Miyazawa et al. show that the contribution of the C-N stretch to the amide II band is about 40%, whereas in acetanilide, the results of the authors (Table VIII) indicate that the contribution of this mode to the amide II band is only 15%. In deuterated acetanilide to the band at 1,410 cm. -1 wh~ch is the amide II band, the contlibution of N-D deformation aecreas.*s considerably and that of C -N str~tcb increases being about 37% (Table IX). A similar result was obtained by Miyazawa e t a L in case of deuterated N-methylacetamide, with the difference that in the latter case, the contribution of C-N stretch is much more than that in deuterated acetanilide, being about 67~. This explains the differenee in the fiequencies of the amide II bands in deuterated N-methylacetamide and deuterated acetanilide (Table X). In acetanilide, to the amide HI band, the contribution comes mainly from v (C-CHs), v (C-N) and 8(N-H) vibrations, but to the corresponding band at 1,080cm. -1 in deuterated acetanflide there is no contribution from C - N stretching vibra- tion. This result is similar to that obtained by Miyazawa ct al. 22 in deute- rated N-methylacetamide. It ma), thus be concluded that the amide II and the amide III bands in secondary amides and anilides are due to the combined contribution of 8 (N-H) and v (C-N) vibrafions and the contribution of v (C-N) to the amide II band is less in anilides than in secondary amides. Abbott et al. and Soichi Hayashi recorded the speetra of acetanilide using polarised infra-red )adiation and the assignments

Vibrational Spectra, Vibrations of Acetanilide & N-Deuterated Acetanilide 197

of the authors of the amide II band on the basis of normal vibrational studies is a deviation from that of Abbott etal. and is in agreement with the assitmment of Soichi Hayashi.

The authors assign the bands at 843 cm. -1 and 1,017 cm_ 1 is acetanilide as due to v (C-CH3) and v (N-CsHs) vibrations and similarly the results of the potential energy distributions indicate that the bands at 650 cm. -~, 345 cm. -~ and 279 cm. -1 are due to the bending vibrations of O = C-N, C-CHa and C-N-C6H~ groups respectively. These results also indicate considerable interaction between r (C-CHa) and �91 (C-N-CeH~) vibrations.

ACKNOWLEDGEMENTS

The authors are grateful to Dr. G. S. Sidhu, Director, Regional Researeh Laboratory, for gNing us facilities to work with the computer and to Mr. P. Jagan Mohan Reddy for bis help in the use of the computer for numerical computations. One of us (V.V.C.) wishes to express his sincere thanks to the Council of Scientific and Industrial Research, Government of India, for the award of Senior Research Fellowship.

1. Mizushima, S., Shimanou- chi, T., Nagakura, S., Kuratani, K., Tsuboi, M., Baba, H. and Fujioka, O.

2. Mizushima . �9

3. Gierer, A. ..

4. Davies, M., Evans. J. and Jones, R. L.

5. Miyazawa, T., Shimanou- chi, T, and Mizushima, S.

6. Mizushima, S. and Shimanouchi. T.

7. Miyazawa, T. �9 �9

8. Kimura, M. and Aoki, M.

9. Suzuki, I.,Tsuboi, M., Shimanouchi, T. and Mizushima, S.

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