Synthesis, Fourier transform infrared and Raman spectra, assignments and analysis of N-(phenyl)- and N-(chloro substituted phenyl)-2,2-dichloroacetamides

Article abstract of DOI:10.1016/j.saa.2003.07.003

N-(phenyl)-2,2-dichloroacetamide (NPA) and N-(chloro substituted phenyl)-2,2-dichloroacetamides of the configuration X_yC ₆H_5-y-NHCO-CHCl₂ (where, X = Cl and y = 1, 2 and 3) were synthesised and the Fourier trans

Full text of DOI:10.1016/j.saa.2003.07.003

Spectrochimica Acta Part A 60 (2004) 1141–1159
Synthesis, Fourier transform infrared and Raman spectra,
assignments and analysis of N-(phenyl)- and
N-(chloro substituted phenyl)-2,2-dichloroacetamides
V. Arjunana, S. Mohanb,∗, S. Subramanianc, B. Thimme Gowdad
a
Department of Chemistry, Tagore Arts College, Pondicherry 605008, India
b
Department of Materials Science, Asian Institute of Medicine, Science and Technology,
Amanjaya, 08000 Sungai Petani, Kedah Darul Aman, Malaysia
Department of Chemistry, Pondicherry Engineering College, Pondicherry 605014, India
c
d
Department of Chemistry, Mangalore University, Mangalore, India
Received 3 June 2003; accepted 1 July 2003
Abstract
N-(phenyl)-2,2-dichloroacetamide (NPA) and N-(chloro substituted phenyl)-2,2-dichloroacetamides of the configuration XyC6H5−y
–
NHCO–CHCl2 (where, X = Cl and y = 1, 2 and 3) were synthesised and the Fourier transform infrared (FTIR) and Fourier transform
Raman (FT-Raman) spectra of the compounds were recorded and analysed. The FTIR spectra of all the compounds were recorded in a Bruker
IFS 66V spectrometer in the range of 4000–400 cm−1 and the FT-Raman spectra were also recorded in the same instrument in the region
3500–100 cm−1. The variation of an amide bond (–NHCO–) parameters with the substitution of the chlorine atom in the phenyl group and the
mixing of different normal modes are discussed with the help of potential energy distribution (PED) calculated through normal co-ordinate
analysis.
© 2003 Elsevier B.V. All rights reserved.
Keywords: FTIR; FT-Raman; Normal co-ordinate analysis; N-(Phenyl)-2,2-dichloroacetamides
1. Introduction
Many acetanilides exhibit fungicidal, herbicidal and phar-
macological activities which has further stimulated recent
interest in their chemistry. N-Phenyl acetamide is used in
medicine under the name antifebrin, as a febrifuge. It is a
useful intermediate in various reactions of aniline in which
it is desirable to protect the amino group. The acetamido
(−NHCOCH3) group is predominantly p-orienting. Anilide
herbicides are promising weed control agents for a wide va-
riety of economically important crops including rice, cotton,
potatoes and corns. The choloroacetanilde herbicide alachlor
is one of the most extensively used of all the agro chemi-
cals [7]. Among the attractive features of these herbicides
are their effectiveness, selectivity and low mammalian toxi-
city [8,9]. Propanil (3,4-dichloropropioanilide) is a selective
contact anilide herbicide recommended for post-emergence
use in rice. It is commonly used for the control of broad
levelled and grass weeds and is the only active substance in
the phyto-pharmaceutical products.
N-Phenyl acetamide (acetanilide) is an interesting system
because the nearly planar amide groups display bond dis-
tances, which are close to those found in polypeptides. Since
the physical properties of hydrogen bonded amide systems
are very sensitive to bond distances, N-phenyl acetamide and
its derivatives to be useful model system in the search for
new physical features of extended polypeptides and perhaps
even natural proteins [1–6]. Spectroscopic and crystal struc-
tural studies give valuable information on bond properties.
Amides are of fundamental chemical interest as conjuga-
tion between nitrogen lone pair electrons and the carbonyl
␲-bond results in distinct physical and chemical properties.
The amide moiety is an important constituent of many bio-
logically significant compounds.
∗
Single crystal Raman, far infrared and inelastic neutron
scattering (INS) spectra of acetanilide in the low frequency
Corresponding author.
E-mail address: s mohan@lycos.com (S. Mohan).
1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2003.07.003

1142
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
(phonon) region were reported [10,11]. The temperature de-
pendence infrared and Raman spectra of N-methylacetamide
[12], acetanilide and deuterated acetanilide [13–15] were
analysed. The vibrational spectra and normal vibrations
of trichloroacetamide have been investigated by Sree Ra-
mulu and Ramana Rao [16]. Vibrational spectra of some
halogen substituted acetamides have been analysed by
Krishnamoorthy and Ramana Rao [17–20]. The spectral
investigation of tertiary amides and related systems has
been reported [21,22]. The Raman and infrared spec-
tra of N,N-diethyl formamide, N,N-diethyl acetamide and
N,N-diethyl chloroacetamide were analysed by Sudarshan
et al. [23]. The IR and Raman spectra of N-(substituted
phenyl)-2,2,2-trichloroacetamides have been analysed [24].
Laser Raman and Fourier transform infrared (FTIR) spectra
of p-nitroacetanilide were recorded and the observed bands
are assigned assuming the molecules belong to the CS point
group [25]. FT-NIR spectra of N-methylacetamide [26] and
the infrared study of dimethylacetamide [27] have been car-
ried out. New investigations of the temperature dependence
of the far-infrared spectra of acetanilide and its isotopomers
have been presented by Spire et al. [28].
Studies of intermolecular associations, dichroic absorp-
tion, band contour of the vapour spectra, measurements of
integrated intensities of the absorption bands and normal
co-ordinate analysis give information regarding the nature
of the functional groups, orbital interactions and mixing of
skeletal frequencies. A systematic study on the vibrational
spectra of simple primary, secondary and tertiary amides re-
ceived considerable attention in the spectroscopic literature
in view of their obvious importance to biological systems.
Despite the wide use of the N-phenyl acetamide family of
molecules in various applications, their spectroscopic prop-
erties are not received much attention. Therefore, we are
interested in the spectroscopic studies of amides and their
derivatives. The main purpose of the present investigation
is to synthesis some substituted N-(phenyl)-2,2-dichloro-
acetamides (NPA), to record the FTIR and Fourier trans-
form Raman (FT-Raman) spectra, to assign the various
fundamental modes precisely, to analyse the fundamen-
tal vibrations completely, to show how the amide bond
(–NHCO–) parameters vary with the substitution of the
chlorine atom in the phenyl group and to analyse the mix-
ing of different normal modes with the help of potential
energy distribution (PED) calculated through normal co-
ordinate analysis. Thus, in the present investigation, we
have undertaken an extensive experimental and theoreti-
cal investigation of N-(phenyl)-2,2-dichloroacetamide and
N-(chloro substituted phenyl)-2,2-dichloroacetamides by
recording their FTIR and FT-Raman spectra and subjecting
them to normal co-ordinate analysis, in an effort to provide
a possible explanations for our observations.
2. Experimental
N-(Phenyl)-2,2-dichloroacetamide and N-(chloro substi-
tuted phenyl)-2,2-dichloroacetamides of the configuration
XyC6H5−y–NHCO–CHCl2 (where, X = Cl and y = 1, 2
and 3) were synthesised from the respective chloroanilines,
dichloroacetic acid and phosphorusoxychloride [24,29].
The pure samples of aniline, respective chloroanilines,
dichloroacetic acid and phosphorus oxychloride were pur-
chased from Aldrich, USA with stated purity and are used
as such without further purification. All other chemicals
employed are of AR grade. Dichloroacetic acid and phos-
phorus oxychloride were mixed together slowly to obtain a
clear mixture. To this aniline/respective chloroanilines has
been added with constant stirring. The mixture was slowly
warmed to expel the hydrochloric acid formed. Cold water
was added to hydrolyse the excess phosphorus oxychloride
present. The hydrochloric acid produced was removed by
treating with excess of 2N sodium hydroxide solution, there
by the crude products were formed, separated, washed with
water and dried. The crude samples were recrystallised
from ethanol. The melting points of the recrystallised sam-
ples were determined. The purity of the compounds was
confirmed by chemical analysis for C, H and N. The FTIR
spectra of all the compounds were recorded in a Bruker
IFS 66V spectrometer in the range of 4000–400 cm−1. The
spectral resolution was 2 cm−1. The FT-Raman spec-
tra of these compounds were also recorded in the region
3500–100 cm−1 using the same instrument with FRA 106
Raman module equipped with Nd:YAG laser source operat-
ing at 1.064 ␮m line with 200 mW power of spectral width
2 cm−1. The frequencies of all sharp bands are accurate
to 1 cm−1. The melting point (m.p.) and the elemental
analysis of the compounds are presented in Table 1.
Table 1
Melting points and elemental analysis of the compounds studied
S. No.
Name of the compound
Melting
point (◦C)
Found (calculated) (%)
C
H
N
1
2
3
4
5
6
7
N-Phenyl-2,2-dichloroacetamide
109
103
127
136
131
88
47.01 (47.07)
40.19 (40.27)
40.22 (40.27)
35.01 (35.18)
35.04 (35.18)
31.11 (31.24)
31.15 (31.24)
3.42 (3.46)
2.49 (2.54)
2.50 (2.54)
1.79 (1.85)
1.80 (1.85)
1.26 (1.31)
1.28 (1.31)
6.81 (6.87)
5.82 (5.87)
5.81 (5.87)
5.03 (5.13)
5.09 (5.13)
4.50 (4.56)
4.99 (4.56)
N-(2-Chlorophenyl)-2,2-dichloroacetamide
N-(4-Chlorophenyl)-2,2-dichloroacetamide
N-(2,3-Dichlorophenyl)-2,2-dichloroacetamide
N-(2,4-Dichlorophenyl)-2,2-dichloroacetamide
N-(2,3,4-Trichlorophenyl)-2,2-dichloroacetamide
N-(2,4,6-Trichlorophenyl)-2,2-dichloroacetamide
187

V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
1143
CHCl2
N
(i) NPA
(ii) 2CPA : X1 = Cl and X2, X3, X4, X5 = H
(iii) 4CPA : X3 = Cl and X1, X2, X4, X5 = H
: X1, X2, X3, X4, X5 = H
H
O
(iv) 23CPA : X1, X2 = Cl and X3, X4, X5 = H
(v) 24CPA : X1, X3 = Cl and X2, X4, X5 = H
(vi) 234CPA : X1, X2, X3 = Cl and X4, X5 = H
(vii) 246CPA : X1, X3, X5 = Cl and X2, X4 = H
X5
X1
X2
X4
X3
Fig. 1. Molecular Structure of N-(phenyl)- and N-(chloro substituted phenyl)-2,2-dichloroacetamides.
3. Normal co-ordinate analysis
frequencies are assigned in terms of fundamental, overtone
and combination bands. To check whether the chosen set of
assignments contributes maximum to the potential energy
associated with the normal co-ordinates of the molecules,
the potential energy distributions are calculated using the
final set of force constants. The potential energy distribution
corresponding to each of the observed frequencies shows
the reliability and accuracy of the spectral analysis.
The general molecular structure of the compounds under
investigation is represented in Fig. 1.
The geometry of the all the molecules under investigation
is considered by possessing CS point group symmetry. The
51 fundamental vibrations of each compound are distributed
into the irreducible representations under CS symmetry as
36 in-plane vibrations of aꢀ species and 15 out of plane
vibrations of aꢀꢀ species, i.e.,
4. Results and discussion
Γvib = 36aꢀ + 15aꢀꢀ
The observed vibrational assignments of the com-
pounds are discussed in four sections. The first section
(Section 4.1) deals with the vibrational characteristics of
N-(phenyl)-2,2-dichloroacetamide while the second sec-
tion (Section 4.2) represents the vibrational assignments
and analysis of N-(2-chlorophenyl)-2,2-dichloroacetamide
(2CPA) and N-(4-chlorophenyl)-2,2-dichloroacetamide (4-
CPA). The vibrational analysis of N-(2,3-dichlorophenyl)-2,
2-dichloroacetamide (23CPA) and N-(2,4-dichlorophenyl)-
2,2-dichloroacetamide (24CPA) are discussed in the third
section (Section 4.3) and in the final section (Section 4.4),
we have presented the fundamental vibrational properties of
N-(2,3,4-trichlorophenyl)-2,2-dichloroacetamide (234CPA)
and N-(2,4,6-trichlorophenyl)-2,2-dichloroacetamide (246-
CPA).
All vibrations are active in both IR and Raman.
Normal co-ordinate analysis provides a more quantitative
description of the vibrational modes. Owing to the complex-
ity of the molecule (51 intramolecular vibrations expected),
a normal co-ordinate analysis is carried out to obtain a more
complete information of the molecular motions involved in
the normal modes of N-(phenyl)- and N-(chloro substituted
phenyl)-2,2-dichloroacetamides, and also for a complete as-
signment of infrared and Raman spectra of these molecules.
Wilson’s FG matrix method [30–32] was used for the nor-
mal co-ordinate analysis in which the normal co-ordinates
are defined with respect to a set of molecular internal
co-ordinates. The normal co-ordinate calculations were per-
formed by utilising the program of Fuhrer et al. [33] with
suitable modifications for computing the G and F matrices
and for adjusting a set of independent force constants. The
structural parameters necessary for these compounds are
taken from Sutton table [34] and structurally related similar
molecules. The initial set of force constants were subse-
quently refined by the damped least square technique. The
simple general valance force field (SGVFF) was employed
for both in-plane and out of plane vibrations in order to
find the potential energy distributions that are characteris-
tics of the force field, so as to avoid any mis-assignment
of frequencies, due to any possible inadequacy of force
constants. The potential energy was expressed by SGVFF
for the following reasons: (a) SGVFF has been shown to
be very effective in normal co-ordinate analysis (NCA)
of benzene and its derivatives. (b) Valence force constants
can be transferred between the related molecules that are
very useful in normal co-ordinate analysis [35]. All the
4.1. N-(Phenyl)-2,2-dichloroacetamide (NPA)
The FTIR and FT-Raman spectra of N-(phenyl)-2,2-di-
chloroacetamide are shown in Figs. 2 and 3. All the ob-
served wavenumbers are assigned in terms of fundamentals,
overtones and combination bands. The observed and calcu-
lated frequencies along with their relative intensities, prob-
able assignments and potential energy distribution of NPA
are summarised in Table 2.
4.1.1. Carbon vibrations
The carbon–carbon stretching modes of the phenyl group
are expected in the range from 1650 to 1400 cm−1. Ben-
zene has two degenerate modes at 1596 cm−1 (e2g) and
1485 cm−1 (e1u). Similarly the frequency of two non-degen-
erate modes observed at 1310 cm−1 (b2u) and 995 cm−1

1144
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
Fig. 2. FTIR spectrum of N-(phenyl)-2,2-dichloroacetamide.
(a1g) in benzene. The actual position of these mode is de-
termined not so much by the nature of the substituents but
by the form of substitution around the ring [36]. Under CS
while the respective Raman bands are observed at 1444,
1396, 1355 cm−1. These frequencies appear in the respec-
tive range and the PED confirms this results and further
shows that these modes are pure.
The in-plane carbon bending vibrations are obtained
from the non-degenerate band at 1010 cm−1 (b1u) and de-
generate modes 606 cm−1 (e2g) of benzene. Likewise, the
CCC out of plane bending modes is defined with reference
=
symmetry, in the case of NPA molecule, the C C stretching
bands appeared at 1601, 1499, 1485 cm−1 in the infrared
and the corresponding Raman frequencies are observed at
1599, 1492, 1479 cm−1. The C–C stretching modes are
assigned to the bands at 1447, 1388, 1344 cm−1 in the IR
Fig. 3. FT-Raman spectrum of N-(phenyl)-2,2-dichloroacetamide.

V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
1145
Table 2
Observed and theoretical wavenumbers (cm−1) and potential energy distribution (PED) for N-(phenyl)-2,2-dichloroacetamidea
Species
Observed wavenumber/int.
Calculated
Assignment
PED (%)
wavenumber
FTIR
FTR
aꢀ
3270 vs
3202 s
3086 s
–
3275 m
–
3087 m
3063 m
–
3020 s
2997 m
2900 m
–
2795 vw
–
3271
N–H stretching
2 × 1601
97νNH
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
3081
3054
3041
3017
2996
2908
C–H stretching
C–H stretching
C–H stretching
C–H stretching
C–H stretching
C–H(Cl2) stretching
2 × 1447
92νCH
88νCH
91νCH
84νCH
3048 w
3013 s
2998 w
2900 w
2850 vw
2785 vw
2338 w
1945 w
1867 w
1795 w
1672 vs
1601 vs
1555 vs
1499 vs
1485 s
1447 vs
1388 vw
1344 s
81νCH + 11νCC
72νCH + 15νC–Cl
2 × 1388; 2 × 1396
1672 + 667
1952 vw
–
1305 + 667
1075 + 811
–
2 × 901
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀꢀ
a
aꢀꢀ
aꢀ
aꢀ
aꢀꢀ
aꢀꢀ
a
aꢀꢀ
aꢀꢀ
a
aꢀꢀꢀ
aꢀꢀ
aꢀꢀ
a
aꢀꢀ
aꢀ
aꢀ
aꢀꢀ
aꢀ
aꢀ
aꢀꢀ
aꢀꢀ
a
aꢀꢀ
aꢀꢀ
aꢀꢀ
aꢀꢀꢀ
a
aꢀꢀ
aꢀꢀ
aꢀ
1680 m
1599 s
1568 s
1492 s
1479 m
1444 s
1396 m
1355 s
1684
1599
1557
1494
1481
1443
1390
1366
1341
1311
1301
1290
1274
1240
1211
1170
1072
1021
1000
968
905
860
806
781
764
719
714
687
668
610
551
538
507
516
468
450
C O stretching
74νC
+ 11νCN + 10νCC
=
=
O
=
C C stretching
84νCC
N–H in-plane bending
69βNH + 18βCN + 10βCCC
=
C C stretching
88νCC
=
C C stretching
87νCC
91νCC
C–C stretching
C–C stretching
C–N stretching
C–C stretching
78νCC + 14νCH
88νCN
74νCC + 12νCN + 10νCH
79νCC + 18νCH
66βCH + 21βC–Cl
71βCH + 19βCCC
59νNC + 31νNH
65βCH + 24βCCC
46γCH + 26γC–Cl
74βCH + 10βCCC + 12νCC
58βCH + 21βCCC + 19νCC
62βCH + 26βCCC
94βCCC
1325 m
1305 m
1289 m
1271 vw
1241 s
1217 m
1177 m
1075 w
1029 w
1001 w
971 m
901 m
861 s
811 vs
–
759 vs
729 vs
712 m
686 s
–
C–C stretching
1305 m
1292 s
1268 m
–
1222 m
–
1079 m
1033 w
998 m
967 w
910 m
870 m
810 m
782 m
760 s
–
C–H(Cl2) in-plane bending
C–H in-plane bending
N–C6H5 stretching
C–H in-plane bending
C–H(Cl2) out of plane bending
C–H in-plane bending
C–H in-plane bending
C–H in-plane bending
Trigonal bending
C–H out of plane bending
C–H out of plane bending
Ring breathing
44γCH + 23γCCC
51γCH + 22γCCC
92βCCC
=
C O in-plane bending
74βC
+ 12βCC + 11βCN
=
C–H out of plane bending
CCl2 asymmetric stretching
C–H out of plane bending
N–H out of plane bending
C–H out of plane bending
CCl2 Symmetric stretching
CCC in-plane bending
47γCHO+ 26γCCC + 14γNH
71νC–Cl + 18νCC + 10βCH
64γCH + 29γCCC
715 w
–
71γNH + 16γCCC
56γCH + 30γCCC
667 s
616 vw
558 s
540 w
505 s
672 m
625 s
568 m
539 m
511 m
73νC–Cl + 18νCH + 10νCC
66βCCC + 18βCH
=
C O out of plane bending
44γC
+ 28γCC + 10γCN
=
O
C–C in-plane bending
C–N in-plane bending
CCC in-plane bending
N–C6H5 in-plane bending
C–N out of plane bending
N–C6H5 out of plane bending
C–C out of plane bending
CCC out of plane bending
CCC out of plane bending
CCl2 deformation
54βCC + 21βCH + 22βCN
49βCN + 29βNH
46βCCC + 20βCH + 10νCH
38βNC + 21βNH + 20βCN
479 w
453 vw
422 w
–
–
–
–
–
–
–
483 s
457 m
–
405 m
384 m
345 s
297 s
253 m
238 w
195 m
53γCN + 25γC
+ 14γNH
=
421
401
371
333
288
256
238
191
31γNC + 28γNHO+ 24γCN
58γCC + 31γC–Cl + 10γCH
41γCCC + 26γCH + 28γCN
38γCCC + 30γCN + 26γCH
54δCCl + 24βCH + 11βCC
2
CCl2 twisting
CCl2 wagging
CCl2 rocking
58τCCl + 23ωCCl
2
2
61ωCCl + 21τCCl
71πCCl2 + 19βC–Cl
2
2
a
vs, very strong; s, strong; m, medium; w, weak; vw, very weak, ν, stretching; δ, deformation; β, in-plane bending; γ, out of plane bending; ρ,
rocking; ω, wagging; τ, twisting/torsion.

1146
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
to 703 cm−1 (b2g) and degenerate 404 cm−1 (e2u) modes of
benzene. In the present work, the bands occurring at 616,
540 and 505 cm−1 in the IR and 625, 539 and 511 cm−1
in the Raman are assigned to the CCC in-plane bending
of NPA. The CCC out of plane bending modes of NPA
under CS symmetry is attributed to the Raman frequencies
observed at 384 and 345 cm−1. The CCC in-plane bending
vibrations are described as mixed modes as there are about
20% PED contributions mainly from C–H in-plane bending
and out of plane bending vibrations, respectively. The C–N
in-plane and out of plane bending modes also coupled with
some percentage of carbon–carbon bending vibrations.
In benzene, the ring breathing (a1g) mode and the CCC
trigonal bending (b1u) vibrations exhibit the characteristic
frequencies at 995 and 1010 cm−1, respectively. In NPA, the
ring breathing mode is observed at 861 cm−1 in the IR and
870 cm−1 in Raman while the CCC trigonal bending is seen
at 1001 and 998 cm−1 in the IR and Raman, respectively.
The NCA predicts that these are very pure modes since their
PED contribution are almost 100%.
the medium intensity band at 1217 cm−1 in the IR and the
Raman counterpart is observed at 1222 cm−1. The aromatic
C–H in-plane and out of plane bending vibrations have
substantial contribution from the ring CCC in-plane and
out of plane bending, respectively. The alkyl C–H in-plane
and out of plane bending modes are significantly over-
lapped with C–Cl in-plane and out of plane bending modes,
respectively.
4.1.3. Amide group vibrations
A characteristic feature of the amide group in amide is
the amide-I band. This mode is observed as an IR absorp-
tion peak at about 1680 cm−1 in N-phenyl acetamide. In the
case of N-phenyl acetamide, the amide-I band is raised due
to the delocalisation of the nitrogen lone pair electrons. In
the N-phenyl acetamide structure, there is competition be-
=
tween the phenyl ring and the C O for the lone pair of elec-
trons of the nitrogen. Simple secondary amides absorbs near
1640 cm−1. Amide-I band, the C O stretching mode is the
=
strongest band in the infrared spectrum and appears with di-
minished intensity in the Raman spectrum. Hence, the IR
band observed at 1672 cm−1 is assigned to the amide-I band
of NPA molecule. The Raman counterpart is obtained at
1680 cm−1. The NCA shows that the amide-I band is to be
pure even though it has mixed with the amide-III mode by
11% as well as 10% of C–C stretching.
The N–H in-plane bending and the C–N stretching vibra-
tions are known as amide-II and amide-III bands, respec-
tively. The amide-II band is often intense, almost as intense
4.1.2. C–H vibrations
The aromatic C–H stretching vibrations are normally
found between 3100 and 3000 cm−1. In this region, the
bands are not affected appreciably by the nature of sub-
stituents. The aromatic C–H stretching frequencies arise
from the modes observed at 3062 cm−1 (a1g), 3047 cm−1
(e2g), 3060 cm−1 (b1u) and 3080 cm−1 (e1u) of benzene
and its derivatives. In NPA, the phenyl C–H stretching
modes are observed at 3086, 3048, 3013 and 2998 cm−1 in
the IR and at 3087, 3063, 3020 and 2997 cm−1 in Raman
spectra. The alkyl C–H stretching is observed in the re-
gion 3000−2850 cm−1. Thus, the frequency at 2900 cm−1
in the IR and Raman is attributed to the C–H stretching
of –CHCl2 group. The PED contribution of the aromatic
stretching modes indicates that these are also highly pure
modes as carbon–carbon stretching, while the C–H stretch-
ing in –CHCl2 group is mixed with the C–Cl stretching by
15%.
=
as the C O stretch itself. The N–H in-plane bending some-
times gives rise to an overtone band at about twice the bend-
ing fundamental at around 1500 cm−1. The amide-II band
of NPA appeared as a very strong band at 1555 cm−1 in
the IR and strong mode at 1568 cm−1 in Raman spectra.
The amide-III band is strong in both IR and Raman spec-
tra of NPA observed at 1344 cm−1 in the IR and 1355 cm−1
in Raman. Though we assigned this frequency also to C–C
stretching, the NCA predicts that the potential energy con-
tribution of C–N stretching is very high and exhibits pure
in nature. The amide-II band of NPA mixes with the C–N
in-plane bending to a considerable amount and the CCC
in-plane bending also contributing by 10%.
The aromatic C–H in-plane bending modes of ben-
zene and its derivatives are observed in the region
1300−1000 cm−1. Studies on the spectra of benzene shows
that there are two degenerate e2g (1178 cm−1) and e1u
(1037 cm−1) and two non-degenerate b2u (1152 cm−1) and
a2g (1340 cm−1) vibrations involving the C–H in-plane
bending. These modes are observed in NPA at 1289, 1241,
1177, 1075 and 1029 cm−1 in the IR and, the corresponding
frequencies are obtained in the Raman at 1292, 1247, 1079
and 1033 cm−1. The C–H out of plane bending mode of ben-
=
The C O in-plane bending is called the amide-IV band. In
NPA molecules, it is assigned to the very strong IR band at
811 cm−1 and in Raman spectra at 810 cm−1. The amide-V
band is known as N–H out of plane bending vibration. This
mode gives rise to a medium to weak band. In NPA, this
mode is assigned to the wavenumber 712 and 715 cm−1
=
in the IR and Raman spectra, respectively. The C O out
zene derivatives are observed in the region 950–600 cm−1
.
of plane bending, amide-VI band of NPA which occur at
558 cm−1 in IR. The corresponding Raman frequency is ob-
served at 568 cm−1. The amide-IV and amide-V bands have
significant contributions from C–N and C–C in-plane and
out of plane bending, respectively. The N–H out of plane
bending mode overlap with the ring CCC out of plane bend-
ing by 16%.
The C–H out of plane bending results from b2g (985 cm−1),
e2u (970 cm−1), e1g (850 cm−1) and a2u (671 cm−1) modes
of benzene. In the present case, these bands occur in the
said region and are presented in Table 2. The alkyl C–H
in-plane bending is assigned to the mode at 1305 cm−1
and the corresponding out of plane vibration is ascribed to

V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
1147
4.1.4. N–H stretching
stretch and C–H in-plane bending modes where as the sym-
metric CCl2 stretching is mixed with the C–C and C–H
stretching mode. CCl2 wagging and twisting vibrations ef-
fectively mixed with each other and also the in-plane C–H
and C–C bending vibrations contributed to CCl2 deforma-
tion and rocking modes.
Secondary amides are the most common and important
type of amide contains only one N–H stretching band in
the infrared spectrum. This band appears between 3370 and
3170 cm−1. The exact location of the N–H stretching mode
depends upon the other groups adjacent to the –CONH–
skeleton. In more concentrated solution and in solid sam-
ples, the free N–H band is replaced by a multiple bands in
the 3330−3060 cm−1 region. Thus, the very strong band ob-
served at 3270 cm−1 in IR and in the Raman at 3275 cm−1
is attributed to the N–H stretching of NPA molecule. The
NCA shows that this is an absolute mode.
4.2. N-(2-Chlorophenyl)-2,2-dichloroacetamide (2CPA)
and N-(4-chlorophenyl)-2,2-dichloroacetamide (4CPA)
The FTIR and FT-Raman spectra of N-(2-chlorophenyl)-
2,2-dichloroacetamide (2CPA) and N-(4-chlorophenyl)-2,2-
dichloroacetamide (4CPA) are presented in Figs. 4–7. The
theoretical and observed wavenumbers of the fundamental
vibrations of both the compounds along with their relative
intensities and potential energy distribution of the individual
mode is presented in Table 3. The correlation of the amide
(–CONH–) group vibrational frequencies are summarised in
Table 6.
4.1.5. C–Cl vibrations
The C–Cl absorption is observed in the broad region be-
tween 850 and 550 cm−1. When several chlorine atoms are
attached to one carbon atom, the band is usually more in-
tense and at high frequency end of the assigned limits. In
view of this, the very strong band in IR at 759 cm−1 hav-
ing a strong Raman counterpart at 760 cm−1 is assigned to
the asymmetric stretching. The symmetric CCl2 stretching
in NPA is observed at 667 cm−1 in IR and at 672 cm−1 in
Raman. The in-plane CCl2 deformation and rocking vibra-
tions are obtained at a low frequency region of the Raman
spectra corresponding to 297 and 195 cm−1, respectively.
The out of plane CCl2 wagging and twisting modes are as-
signed to the Raman frequencies of 238 and 253 cm−1, re-
spectively. These assignments are in good agreement with
the literature [37]. From the PED we observed that the asym-
metric CCl2 stretching moderately overlapped with the C–C
4.2.1. Amide group vibrations
The N–H stretching frequency of 2CPA is found at
3255 cm−1 in the IR and 3253 cm−1 in Raman. For 4CPA,
the bands at 3277 cm−1 in the IR and 3269 cm−1 in Raman
are assigned to the N–H stretching vibration. By com-
parison, we observed that the N–H stretching of 2CPA is
lowered by 20 cm−1 than that of NPA while there is no
change in this frequency of 4CPA. In N-phenyl acetamide,
=
the C O and N–H bonds may be either cis or trans to each
other. But the dipole moment measurements demonstrated
Fig. 4. FTIR spectrum of N-(2-chlorophenyl)-2,2-dichloroacetamide.

1148
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
Fig. 5. FT-Raman spectrum of N-(2-chlorophenyl)-2,2-dichloroacetamide.
the trans conformer is the predominant and stable. Infrared
spectroscopy is one of the most widely used methods to
study the nature and dynamics of hydrogen bonded systems.
A molecule exhibiting hydrogen bonding alters its infrared
frequency in a highly dramatic fashion. Clear manifestations
of hydrogen bonding are large frequency shift and band
broadening of the donors hydrogen stretching vibration.
The influence of a ring substituent on N–H stretching fre-
quency of these compounds under investigation may be the
resultant of steric, direct field effect, hydrogen bonding and
bond polarisation effects. In an ortho-chloro, bromo or nitro
substituted N-phenyl acetamide molecules, the formation of
intramolecular hydrogen bond is further favoured the trans
conformation.
Fig. 6. FTIR spectrum of N-(4-chlorophenyl)-2,2-dichloroacetamide.

V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
1149
Fig. 7. FT-Raman spectrum of N-(4-chlorophenyl)-2,2-dichloroacetamide.
The mesomeric and inductive effects of para substituents
have little influence on the N–H stretching vibrations of
these amides and it is reasonable to assume the polarisa-
tion interactions of an ortho substituent, likewise, have little
effect on the N–H stretching frequency [38]. The steric ef-
fect of ortho substituent must be considered in conjunction
with the conformations. The increase in N–H stretching fre-
quency may be expected in introduction of an ortho methyl
or t-butyl group into the phenyl ring of N-phenyl acetamide.
It is not due to the direct field effect but because of the steric
interactions.
Likewise, the other ortho substituents chloro, bromo, ni-
tro, methoxy groups may produce increase in N–H stretch-
ing frequency of N-phenyl acetamide by exerting steric com-
pression on the N–H bond, but in addition, these substituents
exerts intramolecular hydrogen bonding and also an appre-
ciable direct field effects.
The frequencies observed at 1545 and 1555 cm−1 in IR
are ascribed to the amide-II band of 2CPA and 4CPA, re-
spectively. The corresponding Raman counterpart obtained
at 1551 and 1558 cm−1. The C–N stretching modes of 2CPA
is assigned at 1340 and 1346 cm−1 in IR and Raman spec-
tra. The strong fundamental modes observed at 1338 and
1350 cm−1 in IR and Raman is attributed to C–N stretch-
=
ing of 4CPA. The amide-IV, C O in-plane bending of 2CPA
is found at 807 cm−1 in IR and 804 cm−1 in Raman. The
fundamental modes 801 and 800 cm−1 are attributed to the
=
C O in-plane bending of 4CPA molecule. The amide-V, the
N–H out of plane bending is observed at 739, 742 cm−1 in
2CPA and at 745, 749 cm−1 in 4CPA. The C O out of plane
=
bending of 2CPA is seen at 574 cm−1 in IR, the correspond-
ing frequency of 4CPA is observed at 574 and 584 cm−1 in
IR and Raman spectra.
The other amide group vibrations of 2CPA and 4CPA
molecules exhibit their characteristics in a similar fashion.
When compared these modes of 2CPA and 4CPA with that
of the amide group frequencies of NPA molecule, no appre-
ciable changes in the magnitude of these modes are observed
except the N–H out of plane bending mode. The amide-V,
mode of 2CPA and 4CPA is shifted to higher frequency
by 30 cm−1 than in NPA. The PED calculations determine
that the amide-I, amide-II, amide-IV and amide-VI bands
possessing the character of C–N and C–C vibrations. The
amide-III and amide-V bands are significantly overlapped
with the N–H stretching and CCC out of plane bending vi-
brations.
In 2CPA, the expected lowering of N–H stretching fre-
quency is observed. This lowering of N–H frequency in
2CPA than that of NPA shows the presence of strong in-
tramolecular hydrogen bonding between the chlorine atom
connected at the ortho position and the hydrogen of the
amide group. The intramolecular hydrogen bonding is con-
sidered to be the predominant effect than the steric factor.
Steric compressions and the direct field effects exerted by
ortho substituents may offset the depression.
The amide-I band of 2CPA is found at 1678 cm−1 in IR
and 1685 cm−1 in Raman while in 4CPA the corresponding
frequencies are observed at 1676 and 1682 cm−1. The in-
=
crease in wavenumber of C O stretching in 2CPA and 4CPA
than that of NPA molecule reveals that the substitution of
chlorine in the phenyl ring makes the molecule effectively
compete with the carbonyl oxygen for the electrons of the ni-
4.2.2. Carbon vibrations
The frequency of e2g degenerate pair in benzene is fairly
insensitive to substitution. Similarly, the frequency of e1u
vibrations pair is also not very sensitive to substitution,
=
trogen, thus increasing the force constants of the C O bond.

1150
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
Table 3
Observed and theoretical wavenumbers (cm−1) and potential energy distribution (PED) for N-(2-chlorophenyl)- and N-(4-chlorophenyl)-2,2-dichloro-
acetamidesa
Species
Observed wavenumber/int.
Calculated
Assignment
PED (%)
wavenumber
N-(2-Chlorophenyl)-2,
N-(4-Chlorophenyl)-2,
2-dichloroacetamide
2-dichloroacetamide
FTIR
FTR
FTIR
FTR
aꢀ
3255 s
–
3176 w
3104 w
–
3052 m
3011 m
–
2889 w
–
3253 w
–
3277 vs
3207 s
–
3106 s
3094 s
–
3269 m
3201 w
–
3104 w
3091 m
3057 s
3000 m
–
2886 m
–
2789 vw
–
3258
N–H stretching
95νNH
2 × 1617; 2 × 1600
–
2 × 1588
aꢀ
aꢀ
aꢀ
aꢀ
3100 m
3086 m
3045 w
3009 s
2992 m
2892 m
–
3101
3085
3044
3002
C–H stretching
91νCH
88νCH
94νCH
84νCH + 11νCC
C–H stretching
C–H stretching
C–H stretching
–
2986 m
2891 w
2853 vw
2793 w
2360 w
–
2 × 1499; 2 × 1492
C–H(Cl2) stretching
1555 + 1419
aꢀ
2881
–
84νCH + 10νC–Cl
–
2796 vw
–
1676 + 1098; 1682 + 1100
1678 + 684; 1676 + 687
1551 + 804; 1545 + 807
1095 + 804; 1098 + 801
2360 m
2337 m
–
2346 w
1905 w
1685 s
1591 s
1551 m
1499 m
1471 s
1449 m
1422 w
1346 m
–
–
1892
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀꢀ
a
1678 vs
1593 m
1545 vs
1500 w
1475 m
1446 s
1425 vw
1340 m
1676 vs
1617 vs
1555 vs
1492 vs
–
1447 m
1419 s
1338 s
1682 vs
1600 s
1558 vs
1501 s
1472 s
1441 w
1415 m
1350 s
1681
1599
1542
1500
1467
1442
1421
1338
C O stretching
71νC
+ 14νCN + 10νCC
=
=
O
=
C C stretching
90νCC
N–H in-plane bending
61βNH + 16βCN + 10βCC
=
C C stretching
80νCC
=
C C stretching
74νCC
91νCC
C–C stretching
C–C stretching
C–N stretching
C–C stretching
C–C stretching
N–C6H5 stretching
C–H(Cl2) in-plane bending
C–H(Cl2) out of plane bending
C–H in-plane bending
C–H in-plane bending
C–H in-plane bending
C–H in-plane bending
C–H out of plane bending
C–H out of plane bending
Trigonal bending
68νCC + 24νC–Cl
61νCN + 21νNH
64νCC + 28νCN
61νCC + 24νCH
54νNC + 24νCH
68βCH + 26βCC
38γCH + 30γC–Cl
72βCH + 14βCCC
56βCH + 30βCCC
61βCH + 26βCCC
70βCH + 24βCCC
41γCH + 26γCCC
54γCH + 20γCCC
96βCCC
–
1299 s
1271 m
1241 s
1225 m
1189 s
1130 m
1095 m
1070 m
1052 m
1037 s
1007 s
971 vw
939 m
879 m
804 m
779 m
742 s
1296 m
1281 m
1241 s
1213 m
1177 s
1119 w
1098 vs
1075 m
–
1034 vw
1015 m
967 m
–
1294 s
1273 m
1242 w
1219 m
1187 m
1121 w
1100 s
1073 w
1050 m
–
1009 m
–
935 m
880 m
800 s
1292
1271
1233
1220
1174
1118
1094
1072
1051
1032
1009
970
941
870
806
766
743
681
652
585
580
551
510
485
461
430
401
378
367
361
344
306
261
244
220
181
1280 m
1238 m
1217 w
1181 m
1128 w
–
aꢀꢀ
aꢀ
aꢀ
aꢀꢀ
a
–
aꢀꢀ
aꢀꢀꢀ
aꢀꢀ
a
1059 m
1034 w
–
975 m
944 w
873 m
807 s
760 vs
739 m
684 m
655 s
574 m
C–H out of plane bending
C–H out of plane bending
Ring breathing
47γCH + 26γCCC + 20γNH
62γCH + 23γCCC
94βCCC
aꢀꢀ
aꢀ
aꢀꢀ
a
866 s
801 vs
767 s
745 s
–
=
C O in-plane bending
61βC
+ 11βCC + 14βCN
=
O
770 m
749m
690 m
648 s
CCl2 asymmetric stretching
N–H out of plane bending
C–Cl stretching
76νC–Cl + 22νCC
aꢀꢀ
aꢀ
aꢀ
aꢀꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀꢀꢀ
aꢀꢀ
a
74γNH + 12γCCC
687 m
657 m
–
69νC–Cl + 16νCC
640 s
574 vw
CCl2 Symmetric stretching
69νC–Cl + 20νCC + 10νCH
=
584 m
C O out of plane bending
40γC
+ 21γCC + 18γCN
=
O
CCC in-plane bending
C–C in-plane bending
C–N in-plane bending
CCC in-plane bending
C–N out of plane bending
N–C6H5 in-plane bending
C–C out of plane bending
N–C6H5 out of plane bending
CCC out of plane bending
CCC out of plane bending
C–Cl in-plane bending
CCl2 deformation
45βCCC + 20βCH + 26βNC
48βCC + 24βCH + 26βCN
51βCN + 32βNH
–
–
–
–
545 m
515 s
483 m
459 m
430 s
552 vw
509 s
490 vw
467 w
433 s
–
556 s
518 w
487 m
462 m
–
49βCCC + 25βCH + 24βCN
51γCN + 30γC
+ 10γNH
=
422 w
–
–
38βNC + 21βNHO+ 21βCN
402 m
381 m
407 s
385 s
31γCC + 20γC
+ 16γC–Cl
=
aꢀꢀ
aꢀꢀ
aꢀꢀ
aꢀꢀ
aꢀꢀ
a
–
28γNC + 21γNHO+ 21γNC
38γCCC + 24γCH + 16γCN
40γCCC + 28γCH + 18γCN
49βC–Cl + 29βCH + 24βCC
–
–
–
–
–
–
–
364 s
341 s
301 m
260 m
245 s
222 m
185 m
–
–
–
–
–
–
–
360 m
339 s
305 m
263 w
242 w
219 m
180 w
51δCCl + 20βCH + 11βCC
2
CCl2 twisting
CCl2 wagging
C–Cl out of plane bending
CCl2 rocking
51τCCl + 29ωCCl
2
2
aꢀꢀ
aꢀꢀ
aꢀ
48ωCCl + 31τCCl
2
2
39γC–Cl + 24γC
+ 22γCH
=
O
65πCCl + 29δCCl
2
2
a
vs, very strong; s, strong; m, medium; w, weak; vw, very weak, ν, stretching; δ, deformation; β, in-plane bending; γ, out of plane bending; ρ, rocking;
ω, wagging; τ, twisting/torsion.

V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
1151
although heavy halogens cause undoubtedly diminish the
attributed to the asymmetric and symmetric CCl2 stretching
vibrations, respectively. The phenyl C–Cl stretching mode
of 2CPA is observed as a medium band at 684 cm−1 in IR
and 687 cm−1 in Raman, whereas in 4CPA it is found only
in Raman at 690 cm−1. The strong Raman bands at 341
and 339 cm−1 are assigned to the C–Cl in-plane bending
whereas the out of plane bending is assigned to the medium
bands observed at 222 and 219 cm−1 in Raman for 2CPA
and 4CPA, respectively. The other vibrations of CCl2 like
deformation, rocking, wagging and twisting modes of 2CPA
and 4CPA are observed in the similar region as in the case
of NPA molecule and are presented in Table 3. The contri-
bution of the corresponding C–Cl vibrations observed about
70% and hence these modes are also pure modes. In the
low frequency region of the infrared and Raman spectra of
2CPA and 4CPA, mainly the C–Cl in-plane and out of plane
bending modes are extensively mixed with other modes.
=
frequency [39]. The C C stretching of 2CPA is found in the
IR spectrum at 1593, 1500, 1475 cm−1 and at 1591, 1499,
1471 cm−1 in Raman. Similarly, the very strong lines ob-
served in the infrared spectrum of 4CPA at 1617, 1492 cm−1
and in the Raman at 1600, 1501, 1472 cm−1 are ascribed to
=
the C C stretching modes. The C–C modes of 2CPA and
4CPA are given Table 3. These are all considered to be ab-
solute modes according to the normal co-ordinate analysis.
4.2.3. C–H vibrations
The C–H present in the phenyl ring of 2CPA gives bands
at 3104, 3052, 3011 cm−1 in IR and at 3100, 3086, 3045,
3009 cm−1 in Raman. In 4CPA, these modes are obtained
as strong bands in IR at 3106 and 3094 cm−1 while in Ra-
man these are observed at 3104, 3091, 3057 and 3000 cm−1
.
The alkyl C–H stretching frequency of 2CPA and 4CPA is
observed at 2889, 2891 cm−1 in IR and 2892, 2886 cm−1
in Raman, respectively. All other in-plane and out of plane
bending vibrations of C–H mode is presented in Table 3.
4.3. N-(2,3-Dichlorophenyl)-2,2-dichloroacetamide
(23CPA) and N-(2,4-dichlorophenyl)-2,2-dichloroacetamide
(24CPA)
4.2.4. C–Cl vibrations
Three frequencies are expected in the region 800−
550 cm−1, whose origin can be attributed to the stretching
vibrations of CCl2 group and the phenyl C–Cl bond. The
asymmetric stretching mode of CCl2 in 2CPA is observed
at 760 cm−1 in IR and 779 cm−1 in Raman. Strong infrared
band at 655 cm−1 and medium Raman band at 657 cm−1 are
ascribed to the symmetric CCl2 stretching mode of 2CPA.
In 4CPA, the bands at 767, 770 cm−1 and 640, 648 cm−1 are
The FTIR and FT-Raman spectra of N-(2,3-dichloro-
phenyl)-2,2-dichloroacetamide and N-(2,4-dichlorophenyl)-
2,2-dichloroacetamide are shown in Figs. 8–11. The
vibrational assignments of these compounds are made on the
basis of observed frequencies and their relative intensities in
FTIR and FT-Raman spectra together and potential energy
distribution of the fundamental frequencies calculated from
the normal co-ordinate analysis are presented in Table 4.
Fig. 8. FTIR spectrum of N-(2,3-dichlorophenyl)-2,2-dichloroacetamide.

1152
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
Fig. 9. FT-Raman spectrum of N-(2,3-dichlorophenyl)-2,2-dichloroacetamide.
4.3.1. N–H stretching
substituted compounds and NPA by around 50 cm−1 con-
firm the presence of intramolecular hydrogen bonding.
The strong IR band observed at 3218 cm−1 and a weak
Raman band at 3215 cm−1 is assigned to the N–H stretch-
ing mode of 23CPA. In 24CPA, the N–H stretching mode
is attributed to the medium band at 3199 cm−1 in infrared
and 3210 cm−1 in Raman. The N–H stretching of 24CPA is
shifted to lower frequency by 15 cm−1 when compared to
23CPA. The N–H stretching frequency of 23CPA and 24CPA
molecules are significantly lowered than the monochloro
4.3.2. Amide group vibrations
=
The C O stretching of 23CPA and 24CPA are observed at
1684, 1682 cm−1 in infrared and 1680, 1685 cm−1 in Raman
spectra, respectively. The amide-II, amide-III, amide-IV and
amide-VI vibrations of 23CPA and 24CPA are observed as
almost equal in magnitudes and also not deviated much from
Fig. 10. FTIR spectrum of N-(2,4-dichlorophenyl)-2,2-dichloroacetamide.

V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
1153
Fig. 11. FT-Raman spectrum of N-(2,4-dichlorophenyl)-2,2-dichloroacetamide.
the corresponding frequencies of NPA. The N–H out of plane
bending of 23CPA and 24CPA produce significant frequency
shift from that of NPA. It has 14% contribution from CCC
out of plane bending vibrations.
their origin in –CONH– moiety and carbon vibrations. The
=
C C stretching modes of 234CPA are observed in IR at
1531 and 1445 cm−1 while in Raman these are ascribed
to the frequencies 1535, 1449 and 1429 cm−1. In 246CPA,
=
the C C fundamental modes are assigned to the frequen-
4.3.3. C–Cl vibrations
cies of 1532, 1453, 1432 cm−1 in IR and the Raman coun-
terpart at 1535, 1447 and 1430 cm−1. Similarly, the C–C
stretching modes of 234CPA are obtained at 1393, 1371,
1330 cm−1 in the infrared, the corresponding Raman fre-
quencies are assigned at 1389, 1368, 1328 cm−1. In 246CPA,
these modes are observed at 1392, 1374, 1332 and 1398,
1368, 1331 cm−1 in the infrared and Raman spectra, respec-
tively. Although the carbon–carbon vibrations are consid-
ered to be fairly insensitive to the substitutions in the phenyl
ring these cause decrease in frequency by heavy halogen
substitution. In the cases of 234CPA and 246CPA, the fre-
quency of carbon–carbon stretching shifted to lower fre-
quency side when compared to other compounds studied
in the present work. That is, the carbon–carbon stretching
modes vary from 1601 to 1325 cm−1 in the infrared of NPA
while in Raman from 1599 to 1355 cm−1. But in the case
of 234CPA and 246CPA the range of these modes are ob-
tained between 1531 and 1272 and, 1532−1254 cm−1 in
the infrared, respectively. Similar trends are also noticed in
the Raman spectra of 234CPA and 246CPA. Thus, the vi-
brational bands corresponding to the e2g mode of benzene
and its derivatives, which appears at 1596 cm−1, and the e1u
mode at 1485 cm−1 are lowered in these chloro substituted
N-phenyl acetamide and is very significantly pronounced in
234CPA and 246CPA.
The C–Cl stretching of 23CPA and 24CPA are found in
the expected range. The frequencies seen at 694 cm−1 in
infrared and 715, 689 cm−1 in Raman are ascribed to the
C–Cl stretching in 23CPA while in 24CPA it is observed
at 707, 692 cm−1 in IR and 704, 687 cm−1 in Raman, re-
spectively. The CCl2 asymmetric and symmetric stretching
frequencies of 23CPA and 24CPA does not show any varia-
tion from that of the corresponding frequencies in NPA. The
CCl2 wagging mode significantly overlap with CCl2 twist-
ing mode and vice versa. Similarly the aromatic C–Cl out of
plane bending modes also have more than 20% CCC out of
plane bending contribution. The NCA shows that C–N, N–C
and CCC out of plane bending vibrations strongly coupled
with other modes and the original character of the respective
mode is only about 50%.
4.4. N-(2,3,4-Trichlorophenyl)-2,2-dichloroacetamide
(234CPA) and N-(2,4,6-trichlorophenyl)-2,2-
dichloroacetamide (246CPA)
The Figs. 12–15 represent the FTIR and FT-Raman spec-
tra of 234CPA and 246CPA. The observed and calculated
vibrational frequencies, the assignments of different vibra-
tional fundamental modes and the potential energy contri-
bution of the individual modes are given in Table 5. The
results presented in Table 5 are self explanatory. Hence
the discussion is confined mainly to the vibrations having
The aromatic C–H stretching modes of 234CPA are obtai-
ned at 3069 and 3017 cm−1 in IR and, 3075 and 3025 cm−1
in Raman. Likewise, the strong modes present at 3077, 3030

1154
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
Table 4
Observed and theoretical wavenumbers (cm−1) and potential energy distribution (PED) for N-(2,3-dichlorophenyl)- and N-(2,4-dichlorophenyl)-2,2-dichloro-
acetamidesa
Species
Observed wavenumber/int.
Calculated
Assignment
PED (%)
wavenumber
N-(2,3-Dichlorophenyl))-2,
N-(2,4-Dichlorophenyl)-2,
2-dichloroacetamide
2-dichloroacetamide
FTIR
FTR
FTIR
FTR
–
–
–
–
3418 s
3317 s
3199 m
–
–
–
2870 + 548
2 × 1682
aꢀ
3218 s
3157 w
3114 w
–
3054 m
3009 m
2887 vw
2360 m
2338 w
–
3215 w
–
3210 m
–
3211
N–H stretching
2 × 1583
96␯
NH
–
–
–
1684 + 1420
aꢀ
aꢀ
aꢀ
aꢀ
3084 m
–
3007 m
2871 m
–
3075 s
3060 w
–
3078 m
3055 s
3005 m
2877 m
–
3074
3055
3007
2885
C–H stretching
C–H stretching
C–H stretching
C–H(Cl2) stretching
2 × 1179; 1569 + 812
1684 + 662; 1682 + 670
1291 + 548
90␯
CH
88␯
CH
94␯
CH
2870 vw
2361 m
2336 m
1805 w
1720 w
1682 m
1592 m
1569 m
–
81␯ + 10␯ + 11␯
CH
CC
CN
–
–
–
–
–
–
–
1000 + 707
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀꢀ
aꢀ
aꢀꢀ
a
1684 vs
1583 s
1562 s
1542 s
1483 vw
1454 m
1420 s
–
1680 s
1582 s
–
1685 s
1589 m
1567 s
1545 s
–
1462 s
1430 s
1405 m
1342 m
1320 s
1293 s
1273 w
1242 m
1184 s
–
1681
1584
1569
1541
1480
1458
1428
1410
1342
1314
1287
1261
1240
1180
1151
1072
1041
994
940
910
858
814
780
751
710
689
C O stretching
75␯
91␯
+ 16␯
=
=
CC
C
O
CN
=
C C stretching
N–H in-plane bending
72␤NH + 16␤CN + 12␤CC
=
1548 m
1485 m
1454 m
1427 w
1409 s
1345 s
1322 m
1298 m
1267 s
1237 s
1178 m
1152 m
1074 s
1060 m
992 m
937 s
909 w
865 s
816 s
779 s
749 w
715 m
689 m
667 m
651 m
627 m
593 w
571 s
545 w
481 s
459 s
C C stretching
88␯
CC
=
1481 vs
–
C C stretching
79␯
CC
C–C stretching
C–C stretching
C–C stretching
C–N stretching
84␯
CC
–
92␯
CC
1400 s
–
1315 w
1291 s
–
81␯ + 12␯
CC
CN
CH
1340 m
–
88␯
C–C stretching
69␯ + 18␯
CC
CH
–
C–H(Cl2) in-plane bending
N–C6H5 stretching
C–H(Cl2) out of plane bending
C–H in-plane bending
C–H in-plane bending
C–H in-plane bending
C–H out of plane bending
Trigonal bending
61␤CH + 23␤C–Cl
54␯ + 28␯
1273 m
–
1179 s
1158 w
–
1051 m
983 w
–
913 m
–
809 s
781 s
740 m
–
694 m
662 s
–
621 vw
595 m
573 vw
551 vw
–
NC
NH
1244 w
–
42␥CH + 28␥C–Cl
81␤CH + 10␤CCC
1153 m
1081 m
1044 m
1000 w
931 vs
–
861 s
812 vs
775 vs
–
707 s
692 m
670 m
643 s
–
74␤CH + 11␯ + 10␤CCC
CC
1079 vw
–
65␤CH + 29␤CCC
41␥CH + 28␥CCC
96␤CCC
aꢀꢀ
aꢀ
aꢀꢀ
aꢀꢀ
aꢀ
aꢀꢀ
a
998 s
940 m
917 s
855 m
815 m
774 m
752 s
704 m
–
672 m
659 m
625 w
597 s
567 s
549 m
480 m
450 s
C–H out of plane bending
C–H out of plane bending
Ring breathing
61␥CH + 31␥CCC
55␥CH + 28␥NH
94␤CCC
=
C O in-plane bending
69␤C
72␯
+ 14␤CC + 12␤CH
=
C–Cl
O
CCl2 asymmetric stretching
N–H out of plane bending
C–Cl stretching
+ 17␯
CC
aꢀꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀꢀ
aꢀꢀ
aꢀꢀ
aꢀꢀ
a
74␥NH + 14␥CCC
69␯
71␯
68␯
+ 20␤CCC
C–Cl
C–Cl
C–Cl
C–Cl stretching
+ 10␤CCC
671
648
626
594
563
543
474
451
CCl2 Symmetric stretching
CCC in-plane bending
CCC in-plane bending
CCC in-plane bending
+ 11␤CH + 15␤CC
64␤CCC + 15␤CH
69␤CCC + 21␤CH
–
58␤CC + 18␤CH + 11␤CN
=
570 vw
548 s
470 vw
–
C O out of plane bending
41␥C
+ 21␥CC + 11␥CN
=
CN in-plane bending
N–C6H5 in-plane bending
C–N out of plane bending
CC out of plane bending
CCC out of plane bending
N–C6H5 out of plane bending
CCC out of plane bending
C–Cl in-plane bending
C–Cl in-plane bending
CCl2 deformation
CCl2 twisting
CCl2 wagging
C–Cl out of plane bending
C–Cl out of plane bending
CCl2 rocking
53␤CNO+ 30␤NH
41␤NC + 18␤NH + 21␤CN
455 vw
51␥CN + 20␥C
+ 18␥NH
=
O
38␥CC + 26␥C–Cl + 21␥CH
44␥CCC + 21␥CH + 20␥CN
30␥NC + 24␥NH + 21␥NC
38γCCC + 22γCN + 21γCH
64␤C–Cl + 21␤CCC
aꢀꢀ
aꢀꢀ
aꢀꢀ
aꢀ
aꢀꢀ
aꢀꢀ
aꢀꢀ
aꢀꢀ
a
425 vw
–
–
434 s
–
427 s
389 s
428
381
385 m
–
–
–
–
–
–
–
–
355 w
322 s
293 s
252 m
237 w
212 m
192 m
173 w
–
–
–
–
–
–
–
–
352 m
327 m
297 s
259 m
240 w
215 m
197 w
175 w
350
318
295
249
238
215
191
174
69␤C–Cl + 19␤CCC
51δCCl + 20βCH + 11βCC
2
60τCCl + 21ωCCl
2
2
51ωCCl + 28τCCl
2
2
44␥C–Cl + 28␥CCC
aꢀꢀ
aꢀ
56γCCl + 21γCCC
2
68πCCl + 21δCCl
2
2
a
vs, very strong; s, strong; m, medium; w, weak; vw, very weak, ν, stretching; δ, deformation; β, in-plane bending; γ, out of plane bending; ρ, rocking;
ω, wagging; τ, twisting/torsion.

V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
1155
Fig. 12. FTIR spectrum of N-(2,3,4-trichlorophenyl)-2,2-dichloroacetamide.
and 3073, 3029 cm−1 are assigned to the C–H stretching
modes in 246CPA.
1689 cm−1, respectively, in the infrared. The corresponding
Raman bands are seen at 1685 and 1687 cm−1. The amide-I
mode of the parent compound NPA is found at 1672 cm−1
in the infrared and 1680 cm−1 in Raman. The compari-
son clearly shows a slight increase in amide-I frequency of
234CPA and 246CPA. Similarly the other frequencies re-
lating to amide-II, amide-III, amide-IV and amide-VI band
does not show any appreciable variation when compared to
4.4.1. Amide group vibrations
The amide group vibrational frequencies of 234CPA and
246CPA are found very close to each other and there is no
difference in their magnitudes. The 234CPA and 246CPA
=
shows very strong C O absorption frequencies at 1688 and
Fig. 13. FT-Raman spectrum of N-(2,3,4-trichlorophenyl)-2,2-dichloroacetamide.

1156
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
Fig. 14. FTIR spectrum of N-(2,4,6-trichlorophenyl)-2,2-dichloroacetamide.
observed at 3211 cm−1 in 246CPA. The frequencies at
3217 cm−1 and 3219 cm−1 in Raman belongs to 234CPA
and 246CPA, respectively. As explained earlier, the N–H
stretching frequency is more influenced by the presence of
intramolecular hydrogen bonding in ortho-chloro substi-
tuted compounds and found that the depression in magni-
tude of N–H stretching is more in the cases of 234CPA and
246CPA.
NPA molecule and others. But the correlation of amide-V
band of 234CPA and 246CPA with that of NPA clearly in-
dicates that the frequencies are increased very significantly
by about 40−50 cm−1 with that of NPA.
4.4.2. N–H stretching
The N–H stretching frequency of 234CPA is assigned
to a very strong IR mode at 3219 cm−1 and the same is
Fig. 15. FT-Raman spectrum of N-(2,4,6-trichlorophenyl)-2,2-dichloroacetamide.

V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
1157
Table 5
Observed and theoretical wavenumbers (cm−1) and potential energy distribution (PED) for N-(2,3,4-trichlorophenyl)- and N-(2,4,6-trichlorophenyl)-
2,2-dichloroacetamidesa
Species
Observed wavenumber/int.
Calcluated
Assignment
PED (%)
wavenumber
N-(2,3,4-Trichlorophenyl)-2,
N-(2,4,6-Trichlorophenyl)-2,
2-dichloroacetamide
2-dichloroacetamide
FTIR
FTR
FTIR
FTR
3370 w
3219 vs
3134 s
–
3374 vw
3211 vs
3125 m
3077 s
3030 s
2899 w
2859 w
2707 vw
2359 vw
2338 vw
–
1689 vs
1568 vs
1532 vs
1453 s
1432 w
1392 m
1374 s
1332 s
–
2 × 1688; 2 × 1689
N–H stretching
aꢀ
3217 w
–
3075 m
3025 m
2905 m
–
3219 m
–
3073 s
3029 m
2903 m
–
3215
96␯
NH
2 × 1573; 2 × 1568
aꢀ
aꢀ
aꢀ
3069 vs
3017 vs
2901 m
2857 m
2714 w
2362 m
2338 w
1892 w
1688 vs
1573 vs
1531 vs
1445 vs
–
3075
3028
2904
C–H stretching
91␯
94␯
81␯ + 10␯
CH
C–H stretching
CH
C–H(Cl2) stretching
1573 + 1272; 1568 + 1264
2 × 1371; 2 × 1374
2 × 1177; 2 × 1179
1688 + 643; 1689 + 652
1330 + 573
CH
CC
–
–
–
–
–
–
–
–
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀꢀ
a
1685 s
1571 s
1535 m
1449 m
1429 s
1389 m
1368 m
1328 m
1687 vs
1569 s
1535 vs
–
1430 m
1398 w
1368 m
1331 m
1681
1572
1531
1448
1431
1390
1368
1330
C O stretching
71␯
+ 20␯
=
=
C
N–H in-plane bending
71␤NHO+ 16␤CCNN + 10␤CC
=
C C stretching
86␯
91␯
88␯
90␯
89␯
88␯
CC
=
C C stretching
CC
=
C C stretching
CC
1393 vw
1371 vs
1330 vs
C–C stretching
C–C stretching
C–N stretching
C–C stretching
N–C6H5 stretching
C–C stretching
C–H(Cl2) in-plane bending
C–H(Cl2) out of plane bending
C–H in-plane bending
C–H in-plane bending
C–H out of plane bending
Trigonal bending
CC
CC
CN
72␯ + 11␯ + 16␯
CC
CH
NH
CH
CN
1272 s
1272 s
1264 m
1269 s
1252
1270
1241
1216
1171
1142
1080
971
930
870
828
791
771
749
760
707
676
648
571
541
52␯ + 33␯
NC
78␯ + 12␯
CC
–
1248 m
–
1247 m
1216 w
1179 s
1140 m
1078 m
978 s
–
864 vs
824 vs
798 vs
–
1245 w
1220 m
1179 m
1143 m
1079 w
979 s
932 m
867 s
829 s
64␤CH + 24␤C–Cl
64␥CH + 20␥CC
70␤CH + 18␤CCC
64␤CH + 28␤CCC
40␥CH + 29␥CCC
94␤CCC
aꢀꢀ
aꢀꢀ
a
1216 m
1177 vs
1148 m
1087 w
983 m
925 vs
867 vw
–
1178 m
1145 w
1083 m
979 s
929 s
869 s
827 s
793 s
777 m
759 m
aꢀꢀ
aꢀ
aꢀꢀ
aꢀ
aꢀ
aꢀꢀ
a
C–H out of plane bending
Ring breathing
51␥CH + 24␥CCC
96␤CCC
=
C O in-plane bending
76␤C
69␯
+ 18␤CN
CC
=
C–Cl
O
799 vs
779 s
755 s
796 s
778 m
759 m
CCl2 asymmetric stretching
CCC in-plane bending
N–H out of plane bending
CCC in-plane bending
C–Cl stretching
C–Cl stretching
CCl2 symmetric stretching
C–Cl stretching
+ 19␯ + 10␤CH
61␤CCC + 21␤CH
aꢀꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀ
aꢀꢀ
aꢀꢀ
aꢀꢀ
a
761 m
68␥NH + 17␥CCC
49␤CCC + 21␤CH + 10␤CN
710 s
679 vs
643 vs
573 s
547 s
703 s
673 s
645 s
575 m
550 s
709 w
–
652 s
571 m
548 w
705 s
674 s
650 s
575 m
549 m
68␯
71␯
35␯
74␯
+ 21␯
C–Cl
C–Cl
C–Cl
C–Cl
CC
+ 19␤CCC
+ 15␯ + 10␯
CC
CH
+ 15␤CCC
=
C O out of plane bending
39␥C
+ 25␥CC + 21␥CN
=
C–C in-plane bending
C–N in-plane bending
65␤CCO+ 28␤CH
500 w
–
505 m
475 m
507 vw
470 vw
–
501
471
55␤CN + 29␤NH
476 m
C–N out of plane bending
CCC out of plane bending
CCC out of plane bending
N–C6H5 in-plane bending
C–C out of plane bending
N–C6H5 out of plane bending
C–Cl in-plane bending
C–Cl in-plane bending
C–Cl in-plane bending
49␥CN + 25␥C
+ 19␥NH
=
O
aꢀꢀ
aꢀꢀꢀ
a
35␥CCC + 25␥C–Cl + 24␥CH
45␥CCC + 25␥C–Cl + 24␥CH
40␤NC + 21␤NH + 20␤CN
33␥CC + 18␥CH + 15␥CN
38␥NC + 25␥NH + 18␥CN
61␤C–Cl + 21␤CCC
455 s
438 vw
–
457 vw
441 m
452 m
435 m
455
440
435 w
aꢀꢀ
aꢀꢀ
aꢀ
aꢀ
aꢀ
405 w
407 m
375 s
351 w
329 m
–
–
–
–
399 m
377 w
350 m
331 s
398
371
346
321
–
–
–
58␤C–Cl + 21␤CCC
51␤C–Cl + 10␤NH
12␤CCC + 14␤CH
+
aꢀꢀꢀ
aꢀꢀ
a
–
–
–
–
–
–
301 m
275 s
247 m
229 s
205 w
190 m
–
–
–
–
–
–
303 w
277 m
250 s
225 w
200 m
185 w
302
264
242
221
201
181
CCl2 deformation
CCl2 twisting
CCl2 wagging
C–Cl out of plane bending
C–Cl out of plane bending
C–Cl out of plane bending
50δCCl + 18βCH + 17βCC
2
58τCCl + 31ωCCl
2
2
51ωCCl + 28τCCl
2
2
aꢀꢀ
aꢀꢀ
aꢀꢀ
41␥C–Cl + 29␥CCC + 11␥CH
51␥C–Cl + 24␥CCC
48␥C–Cl + 14␥CN
10␥CCC + 10␥CH
+
aꢀ
–
169 m
–
168 w
171
CCl2 rocking
71πCCl + 18δCCl + 11βCN
2
2
a
vs, very strong; s, strong; m, medium; w, weak; vw, very weak, ν, stretching; δ, deformation; β, in-plane bending; γ, out of plane bending; ρ, rocking;
ω, wagging; τ, twisting/torsion.

1158
V. Arjunan et al. / Spectrochimica Acta Part A 60 (2004) 1141–1159
Table 6
Correlation of amide (–CONH–) group vibrations of the compounds studied
Compound name
νC
βN–H
νC–N
βC
γN–H
γC
=
O
νN–H
=
=
O
O
FTIR
FTR
FTIR
FTR
FTIR
FTR
FTIR
FTR
FTIR
FTR
FTIR
FTR
FTIR
FTR
NPA
2CPA
4CPA
23CPA
24CPA
234CPA
246CPA
1672
1678
1676
1684
1682
1688
1689
1680
1685
1682
1680
1685
1685
1687
1555
1545
1555
1562
1569
1573
1568
1568
1551
1558
1567
1567
1571
1569
1344
1340
1338
1340
–
1355
1346
1350
1345
1342
1328
1331
811
807
801
809
812
–
810
804
800
816
815
827
829
712
739
745
740
–
715
742
749
749
752
759
759
558
574
574
573
570
547
548
568
–
3270
3255
3277
3218
3199
3219
3211
3275
3253
3269
3215
3201
3217
3219
584
571
567
550
549
1330
1332
755
761
824
4.4.3. Potential energy distribution
bonding. The intramolecular hydrogen bonding is not
To check whether the chosen set of assignments con-
tribute the most to the potential energy associated with
normal co-ordinates of the molecules, the potential energy
distribution has been calculated using the relation
favoured in the para chloro substituted molecule 4CPA.
=
(iii) The amide-I, C O stretching frequency is slightly
shifted to higher wavenumber in the cases of N-(chloro
substituted phenyl) compounds than that of N-(phenyl)-
2,2-dichloroacetamide (NPA). The magnitude of fre-
quency variation is not significantly influenced by the
position and number of chlorine atoms present.
(iv) The comparison of other amide group frequencies of
the compounds did not show any appreciable variation
in the respective wavenumbers. It has also been ob-
served that the amide-V band, the N–H out of plane
bending of N-(chloro substituted phenyl)-compounds
is shifted to higher frequency than the N-(phenyl)-2,2-
diclhoroacetamide.
FiiL2ik
PED =
λk
where PED is the contribution of the ith symmetry
co-ordinate to the potential energy of the vibrations whose
frequency is νk, Fii the force constant evaluated by the
damped least square technique, Lik the normalised ampli-
tude of the associated element (i, k) and λk is the eigen
value corresponding to the vibrational frequency k (λk
=
4π2c2νk2). The PED contribution corresponding to each of
(v) The FTIR and FT-Raman vibrational frequencies of the
compounds under investigations revealed close similar-
ities in the magnitudes of the frequencies of other sim-
ilar modes in spite of the fact that the substituents in
the phenyl ring are at different positions.
the observed frequencies are listed in Table 6.
5. Conclusion
(vi) From the normal co-ordinate analysis we observed that
most of the vibrations of the compounds investigated
are remarkably pure modes with most of them com-
posed of at least 70% of PED and above. Significant
vibration interactions with other fundamentals are also
observed, particularly in the low frequency region. The
PED confirm the reliability and precision of the as-
signment and analysis of the vibrational fundamental
modes.
From the complete vibrational analysis of the FTIR and
FT-Raman spectra of NPA, 2CPA, 4CPA, 23CPA, 24CPA,
234CPA and 246CPA molecules the following observations
are made:
(i) Although the phenyl ring skeletal carbon–carbon
stretching is insensitive to substitution, we found the
substitution of chlorine atom in the ring diminished
the carbon–carbon stretching frequencies particularly
in the case of 234CPA and 246CPA but not much
influenced in other compounds.
References
(ii) The comparison of amide group frequencies of the
compounds under investigation shows that the pres-
ence of intramolecular hydrogen bonding between
the chlorine atom and amide hydrogen specifically in
the ortho-chloro substituted compounds like 2CPA,
23CPA, 24CPA, 234CPA and 246CPA. This is con-
firmed from the observed N–H stretching frequencies
and found lowering in magnitudes of these vibrations
in the case of ortho-chloro substituted compounds
than that of NPA. The depressions in N–H stretching
frequencies relative to NPA are not quantitative in-
dications of the strength of intramolecular hydrogen
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