CHAPTER - 4 VIBRATIONAL SPECTRA AND NORMAL COORDINATE ANALYSIS

OF N,N-DIMETHYL ACRYLAMIDE

4.1 INTRODUCTION

A ryrtematic study of molecular rpectra and structure

of primary, ~ e c o n d a r y and tertiary amidel are of great

significance ln v i e w of thelr obvioua importance to

biological rystemr. Several authors ( 1 - 4 ) have reported the

Raman and infrared spectra of prlmary, secondary and

tertiary amides and carried out the normal coordinate

treatment of these amides in order to asslgn the vibrational

frequencies and investigated the mlxlng up of skeletal

frequencier. The main result that emerges out of these

studies ir that all amides shows a carbonyl absorption band

irnown rr the a m ~ d e I band. Its posltion depends on the

physical state of the compound (5).

In prlmary amides, the amlde 1 , amlde 1 1 and amlde 111

band8 are essentially due to ( C = O ) stretchlng, ( N H 2 )

deformation and ( C - N ) stretchlng vlbrrtlons respectively.

In recondary amider, while the amide 1 band 1s essentially

C.0 rtretch, the rmide I1 and amlde 111 bands have been

shown to arise out of the combined contrlbutlon of ( N - H )

deformation and ( C - N ) atretching vibrationr.

The spectral lnvestlgatlons of tertlary amldes and

related aystems have been the subject matter of several

remearch papers in recent tlmes. Although the spectra of

there erres were reported in detail, their analyslfi are

rome-what tentrtlve. Infrared and Raman spectra wlth

tentative assignments were flrst reported by Jonathan (6).

However, the lnfrared data were llmlted to 450 cm-I and

Raman polarization measurements were not performed. In order

to verify a proposed crystal structure, polarlsed lnfrared

spectra on oriented samples were obtalned by Colthup ( 7 ) who

also proposed ar assignment for a few fundamental modes. The

vibrational spectra were r e i n v e s t ~ g a t e d by Ramana Rao et

a1 ( 8 , 9 ) who also carried out a prellmlnary normal

coordinate calculations. In these works too, Raman

polarization data ,were not reported and the lnfrared spectra

were limited to 400 cm-I. Far-lnfrared vapour phase spectra

of acrylamlde u8ere investigated by Kydd et a1 (10) but these

studiea were mainly devoted to the elucidation of the

moiccular conformation. An assignment of the Raman bands of

acrylamide was also proposed by Gupta Bans11 ( 1 1 ) In

connection with a study of the structure and conformation of

polyacrylamide. A n ~ s n e y u l u et a1 ( 1 2 ) evaluated the

thennodynamic functions of acrylamlde uslng the available

vibrational data. Venkata Ramiah and Ccworkers ( 1 3 )

recorded the lnfrared and Haman spectra of K , N -

dimethyl formamide [DMF] (131, N,N - dimethyl propionamide

[DPA] (141, N,N - dimethyl butyramide [DBA] (15) and N,N - dimethyl thloforrnamide [ D M T F I (16). They have also studied

force field [GVFF] of the above system#, except DBA, by

treating the methyl and ethyl groups as point masses.

Acrylamlde, N, N - dlmethyl acrylamlde and related

systems have been subject matter of several research papers

( 1 7 , 1 8 ) , N, N - dimethyl acrylamide finds extensive

applications as coatings, paper and textiles treating

agents, adhesives and binders. Earller, Hamana Kao and

Venkata Rarniah (18) attempted partially to interpret

infrared and Raman spectra of N,N - dirnethyl acrylamide,

using SVFF and UBFF. Hence the aim of the present work 1s

to investigate the vibratlonal spectra of N, N -dimethyl

acrylamide completely using infrared and laser excited Raman

spectra with a modified eeneral quadratic valence force

field ( M G Q V k F ) and to assign the in-plane and out-of-plane

vibratlonal I requencles.

Spectroscopically pure N,N-dimethyl acrylarnide in

liquid-phase was obtained from Alcolac (BALTIMOHt,USA) and

uaed ?a huch. ?he infrared spectrum of N , h-d~rnethyl

acrylamide was recorded on a Perkln-Elmer 1 K 9 8 3 double beam

grating apectrophotometer in the region 200 - 4000 cm-l.

The Fourier transform far-lnfrared spectrum of the same

sample was recorded In the region 100-500cm-~ uslng Polytech

FIR 30 apectrophotometer. The laser Raman spectrum of the

sample was also recorded i n the region 100 - 4000 cm-' on a

Cary Model 8 2 grating Spectrophotometer equlpped wlth a

spectra Physlcs Model 165 ~ r + Ion laser operating at 4W

power continuously on the 488 nm lrne was used with a

spectral vldth of 2.0 cm-l. The spectra were measured with a

scanning speed of 30 cm-'mln-l. The frequencies for all

sharp bands are accurate to i 1 cm-l. The observed laser

Raman. infrared and far-infrared spectra are shown ~n Flgs

4.1 - 4.3.

4.3 NORMAL COORDINATE ANALYSIS

The normal coordinate analysis based on hilsonls (19)

F-G matrlx method is performed using the Schachtschnelder

(20) programnc ulth a modlflcatlon to sult our system. From

the structural point oi view, this molecule belongs to C s

symnetry and ~t may be rustifled from the crystaliographic

data for a number o f long chain n-fatty acid amldes (21,

22). The tu,o of the hydrogens of each methyl group are

lylng out of !he plane of molecular symnetry. one above and

the other below the plane. The ethylene double bond also

takes part ln givlng a planar structure to thls molecule.

The reprcrrntat~ve structure of the molecule 1s shoun In

Fig. 4.4. For a C s structure, the 42 fundamental vlbratlons

fall into 27 in-plane vibrations of a' specles and I 5 out-

of-plane vibrations of a" specles.

F I G . 4 3 FOURIER FAR -INFRARED SPECTRUM OF N,N-DIMETHYLACRYLAMIDE

The rtructural parameters employed in the present work

are C-N = 1 . 3 1 5 A ' ; C = O = 1 . 2 4 3 A' ; C-C = 1 . 4 7 A' ; C = C =

1 . 1 3 7 k ; C = H (ethelene) = 1 . 0 7 4 ' ; N-C = 1 . 4 7 4 ' ; C-H

(methyl) 1 . 0 9 ~ ' . The angles around methyl carbon atom

ate asrumed to be tedrahedral 1 0 q 2 8 ' : other angles are

taken t o be 120' each. The symnetric coordinates used rn

the preaent work are given in Table 4.1. The inrtial set of

force conrtsnta are taken from acrylamide (lo), N,N-dlmethyl

thioacetamide ( 3 ) and other related molecules. Thls set of

force constant is subsequently reflned by keeplng a few

interaction constant. fixed throughout the refznement

process. The final set of force constants are presented ln

Table 4.2 together with the inltral values.

4.4 RESULTS AND DISCUSSION

4.4.1 Vibrations of m e t h y l Eroup

When the stretching vlbratlons of methyl groups rn

compounds contrlnrng the dlmethyl amlno groups are assigned,

the number of fundamental usually exceeds the number of

bands which reasonably can be ascrlbed to thls ortgln ( 2 3 ) .

From the normal coordinate analysls of N, N - dlmethyl

acrylamide, the bands observed at 3 0 0 7 cm-' In rnfrared and

3005 cm-I in Raman are doubly assigned to asymnetric

stretch o f (CH,)Z o f a' specres. Slmllarly, the strong band

observed at 2 9 3 0 em-' In infrared and its laser Raman

counter part at 2938 cm-'are doubly assigned to

rymnstric etretch of (CH3)Z of a'species.

According to the results of the normal coordinate

analysis on N,N-dlmethyl acrylamlde, the bands observed at

2960 cm-I in lnfrared and 2965 cm-I In Raman are doubly

asslgned to out-of-plane asymnetrlc stretching modes of

(CH3IZ. O n the basis of the calculated vibrational

frequencies and PED, it 1s concluded that the deformatlon

modes of methyl group fall under the reglon 1000-1500 cm-l.

All these modes appear to be mlxed modes. The very weak

bands observed at 1460 cm-I and the strong band at 1462 cm-I

in infrared and Raman are assigned to two asymnetric

deformation of a ' type. The asymnetrlc deformation of ( C H 3 ) 2

belonging to a" species 1s asslgned to the band at 1452

cm-', The weak bands observed at 1410 acd 1375 crn-I In

lnfrared spectrum are asslgned to tu.0 symnetric deforrnatlon

modes of ( C H 3 ) Z .

- 1 T h e strong bands observed at 1140 and 1 0 5 9 cm ln

rnfrared have been asslgned to two rocking modes of ( C H 3 I r

According to the calculated PED, asymnetrlc stretches of

methyl groups in dimethyl amlno groups also contribute tc

the rocking modes of ( C H 3 ) 2 . Slmllarly, the very strong

- 1 Raman band at 1150 cm la doubly asslgned to rocklng modes

o f (CH,)Z o f a " s p e c 1 e s . The weak bands observed at 145 and

128 c m - I in infrared are asslgned to (CHj)? torsional

vibration. The contribution to these modes from asymnetrlc

(CH3)Ldeformation modes is considerable.

4.4.2 Frequency of Ethylene groups

The infrared bands observed at 2830, 3 0 2 5 and 3095 cm-I

are arrigned to C-H stretchlng, symnetrlc and asymnetrlc

rtretching moder of CH2 vibrations, respectively. As

expected these mode8 seem to be pure.

The medlum strong band at 1112 em-' in lnfrared and in

Raman at 1114 cm-' are essentially due to C = C stretchlng

mixing with deformation modes of CH2. The band observed at

985 cm-I In infrared 1s asslgned to C-C symnetrlc stretching

of a' specles,

The strong band observed at 1424 cm-I and the very

weak band at 1302 cm-I In lnfrared are asslgned to the

a s y m e t r l c and symnetric deformatlonal modes of CHZ. This

is in close agreement wlth the earller literature values

( 1 6 , 1 7 ) . The deformatlon mode of C=C-C 1s assigned to the

strong band observed at 414 cm-l In Raman spectrum and from

the calculated PED, ~t 1s clear that it mlxes wlth the C:C

rtretching and deformatlon modes of C-C.

The very weak band observed at 102 crn-I In lnfrared

ham been asalgned to torsional modes of C-C. Thls mode 1s

due to the result of twlsting (CHZ )CH and N(CH3)2C0 group

about the C-C bond in opposlte dlrectlon. Slnce, both the

groups are massive, the torsional mode of C-C has been

assigned to thls low frequency value. The weak band

observed at YbO cm-l in ~ n f r a r e d has been asslgned to

wagging C.CH2 of a " species.

4.4 .3 Frequency of amide group

T h e very strong band observed at 1658 cm-I in lnfrared

which h a s a relatively weak Raman counter part at 1654 cm - 1 is a ~ s i g n e d to C = O stretching mode (amlde band I ) , This

agrees well wlth the earlier literature values (17). The

strong infrared band observed at 1492 cm-l 1s assigned to

C-N stretching (amlde band 1 1 1 ) mode. Similarly,the weak

band observed at 2 6 1 cm-l ln infrared and its Haman counter

part at 270 cm-I are asslgned to torsional C-h mode of atl

species.

T h e symnetrlc and asymnetric C-N stretching

vibrations In N <$:arc assigned by taklng Into account

their characteristics interchange intensity in infrared and

Raman ( 1 7 ) . Thus, the weak ~ n f r a r e d band near 7 6 " cm-l and

the relatively strong band at 1268 cm-l which have strong

and relatively weak Raman counter parts near 760 and 1272

em-' rerpectlvely are asslgnedto symnetrlc and asymnetrlc

C-N stretching modes n h'<:::. The asymnctrlc and symnetrlc

deformatlonal modes of lare re assigned to the weak bands c W3

o b s e r v e d a t 508 and 2 9 5 cm-' An I n f r a r e d s p e c t r u m . The weak

b a n d s o b r e r v e d a t 5 8 0 and 386 cm-' I n l n f r a r e d a r e

e s s e n t i a l l y d u e t o C=O o u t - o f - p l a n e b e n d i n g and (C-N<::; )

wagging of a " s p e c l e s r e s p e c t i v e l y , whlch f a v o u r a b l y a g r e e

w e l l w i t h D u r g a p r a s a d and S a t h y a n a r a y a n a ( 3 ) . The band a t

6 0 2 cm-' i s due t o O=C-N b e n d l n g of a t s p e c l e s .

A s p o i n t e d o u t e a r l i e r t h e f o r c e c o n s t a n t s used i n t h l s

c a l c u l a t i o n were t r a n s f o r m e d from r e l a t e d s t r u c t u r e and t h l s

gave q u i t e c l o s e agreement w l t h o b s e r v e d v a l u e s f o r a l l t h e

a ' s p c c i e r . But t h e agreement was p o o r f o r a n s p e c l e s . The

f a r - i n f r a r e d d a t a o f t h i s sample was v e r y u s e f u l l n t h e

a s s l g n o s n t of low f r e q u e n c y modes. l h e r e f l n e d s e t of f o r c e

f i e l d o b t a i n e d l n t h l r work 1 s comparab le t o t h a t a c h i e v e d

f o r p e p t i d e f o r c e f l e l d ( 2 4 , 2 5 ) .

TABlE - 4.1: SYWTRY COORDINATES FOR THE IN-PLANE VIBHATIONS

OF N,N-DIUETHYL ACWYLAMIDE.

Syrrznetry c o o r d i n a t e s D e s c r i p t i o n

I n - p l a n e V ~ b r a t i o n s S1 = A ] - L k v a S (CH2)

s 2 = h j + h k v S (CH3)

s 3 = 2 A l - A m - A n + 2 h p - h q - A f a s ( C H 3 ) 2

s4 = 2 A 1 - A m - A n - 2 A p + Aq + Af v a s ( C H 3 ) 2

S 5 = A 1 t Am t An - A 7 - A q - Af (CH312

S6 = A1 + Am + An + A p + Aq + A t v , ( C H 3 ) 2

S 7 = A s (C-H)

S s r ~ n ( C = O )

S g = AD V ( C - h )

S10 = 2 Alm - Am1 - A n 1 + 2 A q f - Apq - A p f a s ( C H 3 ) 2

s I 1 = 2 hmn - Am1 - An1 - 2 A q f + A P ~ + Apf b a s ( C H 3 ) Z

S , , : 2 A j k - A t ] - h t k a s ( C H 3 ) 2

S13 = A t j - A t k y (CHZ)

s14 = A m l + Amn + An1 - Aul - bum - b u n

t h p f + Aqf + Apq - Apd - A f d - A q d h s (CH3I2

s I 5 = Am1 t Amn + An1 - Aul - hum - Aun

- b p f - A q f - A p q + Apd- A f d - Aqd 5 s (CH3)2

S I 8 = 2 ~ u l - A u m - d u n - 2 A p d - ~ q d - A f d Y ( c H ~ ) ~

Ou t - o f - p l a n e v i b r a t i o n s

S 2 8 = A m - A n + A q - Af

S 2 9 =Am - A n - A q + A f

3,s (CH3)2

' a s (CH3)2

' a s (CH3)2

' a s ICH3)2

Y (CH3)2

(CH3)2

N<:;; ) $ (C-CH2)

(CH3)2

-T (CH3)2

7: (CH2)

Z (C-C)

TABLE - 4 . 2 : INITIAL AND FINAL SET OP FOHCE CONSTANTS OF'

N,N - DIMETHYL ACHYLMIIDE. ( 1 0 u n i t s o f mdyne % I , d y n e rad- l and d y n e 2-I

rad-2 )

Types of Parameter coordinate Initial Flnal constants lnvolved values values

Dlagonal stretching ft C=C 7.712 7.646

constants

fl C-H 4.500 4.521

fif C-C 2.850 2.751

f~ C-N 6.421 0 . 6 1 2

f d N-C 5.752 5,726

f~ C-H 4.511 4 . 6 1 1

HCH

HCC

NCH

HCH

CNC

OC N

OCC

CCN

CNC

I n t e r a c t i o n s t r e t c h - c o n s t a n t s s t r e t c h t~

~r

RD

rD

s t r e t c h - b e n d tB

DO

C = C C - C 0 . 6 1 4

C - C C - C 0 . 8 6 9

C = C C - N 0 . 4 1 5

C = O L-N 0 . 7 5 1

C-N N-C 0 . 6 5 8

C-H C-H 0 . 3 8 1

NC, NC 0 . 8 1 1

NCv CH 0 , 6 0 2

CH, CH 0 . 3 1 5

C'H CCH 0 , 5 1 4

C N , N C O 0 . 6 0 2

CrO OCH 0 . 4 1 2

C-C CCN 0 . 3 8 9

C h CNC 0 . 4 2 6

NC ChC 0 , 4 5 8

KC NCH 0 . 5 1 2

CH HCH 0 . 2 8 1

CH hCC 0 . 2 6 1

HCC CCH 0 . 1 6 1

NCOOCC 0 . 1 0 7

O C C C C N 0 , 0 1 8

C C N N C O 0 . 0 7 9

C N C C N C 0 . 1 2 1

CNC hCH 0 . 2 0 1

HCHHCH 0 . 0 9 8

f O 1 CO 0 . 5 4 1 0 . 5 6 1

* 0 2 NC 0 . 1 6 2 0 . 1 7 9

0 3 NC 0 . 1 6 2 0 . 1 7 8

Torsion f . t l CC 0 . 1 0 0 0 . 0 8 6

r2 C N 0 . 6 8 0 0 .6 '12

f T 3 N C 0 . 1 0 0 0 . 0 9 2

f r 4 NC 0 . 1 0 0 0 . 0 9 6

I n t e r a c t i o n f O 1 . t 2 COCN 0 . 0 1 1 0 . 0 8 2

f O Z r Z NC CN - 0 . 0 7 0 - 0 . 0 7 9

f 0 3 T 2 NC CN - 0 . 0 7 0 -0.0711

---------------------------------------------------------------.-

T A B U - 4.3 VIBRATIONAL ASSIGNYENTS OF N,N - DIMETHYL ACRYLAMIDE

Spe Observed Frequency Calculated Assignments PED(%) - 1

cles ( c m )and intensity frequency

W ama n

3 1 0 5 W

3 0 3 2 W

3 0 0 5 W

3 0 0 5 W

2 9 3 1 ) 5

2 9 3 8 S

2 8 2 9 S

l b 5 4 H

1 4 9 0 S

1 4 6 2 S

1 1 5 5

l l l b

1 0 6 5

9 8 1

7 7 1

5 9 5

270 VW 27 5 t (C-N) S38(94)

5 : Strong; VS = Very Strong; M = Medlum; MS = Medium Strong;

k 2 h e r k ; VH a V e r y heak: 3 = Symnetry stretching; J 2 Stretching; 3 = Asymnetfy stretchlng;

6 : ~ ~ f ~ ~ ~ ~ r l o n ; 3 = Wagging; 7 = Torsion; v = R o c k ~ n g ; F = Out-of-plane b e n d ~ n g .

1. J . Jakes and S. Krimn, Spectrochlm. Acta., 27A, 1997

(1971).

2. C.N.R. Rao and G.C. Chaturvedl, Spectrochim. Acta., 2 7 A ,

5 2 0 (1971).

3 . G. Durgaprasad, D.N. Sathyanarayana and G. Borch,Chem.

Scand., 25, 2029; 26, 2039 (1971).

4. G. Durgaprasad, D.N. Sathyanarayana and C.C. Patel, H.S.

Handhawa Abha Goel and C.N.R Hao, Spectrochim. Acta.,

28a, 2311 (1972).

5 . M . Silverstein, C-Clayton Bastler and C.Moril1,

USpectrometrlc ldentlflcatlon of organlc Compounds"

John klly, New york (1981).

b. H. Jonathan, J. Molec. Spectrosc., 6, 205 (1961).

7. S.8. Colthup, Paper 98, presented at the Plttsburg

Conference on Analytical Chemistry and Applled

bpectroscopy (1959).

N . B . Colthup, L.H. Oaly and E Wiberley, i n

" l n t r o d u c t ~ o n to Infrared and Haman Spectroscopy", P.Y7,

Academic Press, Boston (1990).

8 . G. Ramana Rao, V. Balasubramanlan and K. Venkata Kamaiah,

Indian J . Pure and Appl. Phys., 13, 546 (1975).

Y . G. Ramana Kao and K. Vcnkrta Hamarah, Indian J. Pure and

Appl. Phye., 1 9 , 593 (1981).

10. R.A. Kydd and A.R.C Dunham, J.Molec. Struct., 69, 7 Y

(1980).

11. M. R. Gupta and H. Banell, J . Polym. Sci.,Polym. Phys. Ed.,

19, 353 (1981).

12. Y . Anjaneyulu, Krlshnan La1 and H.L. Bhatnagar, J .

l n d ~ a n Chem. Soc., 65, 400 (1988).

13. V. Venkata Chalapathl and K. Venkata Ramlah, Curr. Scl.,

68, 109 (1968).

14. V. Venkatachalapathl and K. Venkata Ramlah, Proc, Indian

Acaa. Scl., 37, 453 (1968).

15. ti. Venkata Raniah and P. Shlyamala Krishna Sayee, Curr.

Scl., 38, 457 (1969).

C.A. l n d ~ r a Charry and K. Venkata Ramlah, Proc. 1nd1a11

Acad. Scl., 6 9 , 18 (1969).

S. Mohan, h . Sundaraganesan and Bigatto, Vibrational

Spectrosr., (In Press).

18 . G. Ramana Rao and K . V r n k a t a Ramlah, I n d l a n J . Pu re and

App l . P h y s . , 1 8 , 9 4 ( 1 9 3 9 ) .

1 9 . E.B. W l l s o n , J . Chem. P h y s . , 7 , 1 0 4 7 ( 1 9 3 9 ) ; 9 , Yb

( 1 9 4 1 ) .

20. J.H. S c h r c h t ~ c h n e l d e r , "Technical R e p o r t , S h e l l

D e v e l o p n e n t Company" , E m e r y v l l l e , CA ( 1 9 6 9 ) .

2 1 . J.D, T u r n e r and E.C. L l n g a f e l t e r , A c t a . C r y s t a l l o g r . 8 ,

551 ( 1 9 5 5 ) .

22 . J . R . B r o t h o r d e and E.C. L l n g a f e l t e r , A c t a . C r y ~ t a l l o g r .

1 1 , 729 ( 1 9 5 8 ) .

K . A . J e n s e n , B.M. D a h l , P.H. t i e l l s o n a n d G . B o r c h , Chem.

S c a n d . , 2 5 , 2 0 2 9 ; 2 6 , 2039 ( 1 9 7 1 ) ,

S. Krlmn and J . B a n d e k a r , Adv. P r o t e l n . Chem., 3 8 , 1 8 1

( 1 0 8 6 ) .