Fourier transform infrared spectra and normal mode analysis of 1-[(3-methylphenyl)piperazin-1-yl]-3-[thio(4-acetamido- phenyl]propane: A potent 5-HT2 and D2 receptor ligand

Article abstract of DOI:10.1016/S1386-1425(99)00224-3

1-[(3-methylphenyl)piperazin-1-yl]-3-[Thio(4- acetamidophenyl]propane and its analogs have shown good hypotensive activity and the title compound has shown a profile of centrally acting anti-hypertensive agent. It also binds with the 5-HT₂ rece

Full text of DOI:10.1016/S1386-1425(99)00224-3

Spectrochimica Acta Part A 56 (2000) 1267–1275
www.elsevier.nl/locate/saa
Fourier transform infrared spectra and normal mode
analysis of 1-[(3-methylphenyl)piperazin-1-yl]-3-
[thio(4-acetamido-phenyl]propane:
a potent 5-HT2 and D2 receptor ligand
Rajendra B. Singh a, Dinesh C. Gupta a,*, Umesh C. Bajpai a,
Mridula Saxena a, Anil K. Saxena b
a Department of Physics, Uni6ersity of Lucknow, Lucknow 226 007, India
b Medicinal Chemistry Di6ision, CDRI, Lucknow 226 007, India
Received 1 June 1999; received in revised form 14 September 1999; accepted 14 September 1999
Abstract
1-[(3-methylphenyl)piperazin-1-yl]-3-[thio(4-acetamidophenyl]propane and its analogs have shown good hypoten-
sive activity and the title compound has shown a profile of centrally acting anti-hypertensive agent. It also binds with
the 5-HT2 receptors. The conformation of the title compound was determined by X-ray diffraction but this is not
possible for its analogs because of the difficulty in preparing their single crystals. A novel and easy approach is
envisaged to determine the conformation in such cases by the application of semi-empirical molecular orbital
calculations, Fourier transform infra red (FTIR) spectroscopy and normal mode analysis. As a first step in this
direction the FTIR spectrum of the title compound has been recorded and its normal mode analysis carried out. The
assignments of the frequencies are based on the concept of group frequencies and band intensities. The spectrally
observed frequencies have been tabulated along with the theoretically calculated ones and their assignments. Good
agreement has been obtained between them and a set of 101 force field constants is established. © 2000 Elsevier
Science B.V. All rights reserved.
Keywords: FTIR spectra; Vibrational frequencies; Force constants; Infra red spectral band assignments; Conformation
1. Introduction
1-[(3-methylphenyl)piperazin-1-yl]-3-[thio(4-ace-
tamidophenyl]propane and its analogs have
* Corresponding author. Tel.:+91-522-323728; fax:+91-
shown good hypotensive activity and the title
522-375858.
compound has shown a profile of centrally acting
anti-hypertensive agent [1]. It also binds with the
E-mail address: dinesh
Gupta)
c gupta@hotmail.com (D.C.
– –
1386-1425/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S1386-1425(99)00224-3

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R.B. Singh et al. / Spectrochimica Acta Part A 56 (2000) 1267–1275
formations may then be utilized in establishing
3-D structure-activity relationships.
5-HT2 receptors [2]. The conformation of a drug
molecule plays an important role in drug recep-
tor interactions, which lead to its biological re-
sponse. Several methods are available which
predict such effects [3–6] and provide insight to
active site space and binding requirements, but
most of these are biased due to arbitrarily cho-
sen molecular overlays on binding site points.
The conformation of the title compound was de-
termined by Carpy et al. [7] using X-ray diffrac-
tion, but such determinations are very difficult
for several of its analogs as they can not be
grown into single crystals.
As a first step in the application of the above
approach to the present series of analogs, the
title compound has been chosen because its X-
ray determined structure is available [7]. This
has been utilized in carrying out its normal
mode calculations. The FTIR spectrum has been
recorded and a set of force field constants has
been established to obtain a good agreement be-
tween the theoretical frequencies and the ob-
served spectra. These results are presented in
this paper. The work on the analogs is in pro-
gress and will be reported very soon.
Facing a similar problem in the case of the
analogs of a potent anti-hypertensive agent 1-
[(3-methylphenyl)
piperazin-1-yl)-2-(quinolin-2-
2. Materials, methods and theory
yl)ethane (centhaquin) the authors envisaged a
new and simple way out [8]. In this approach,
the conformation of the compound is deter-
mined using the semi-empirical molecular orbital
method. Experimental support to such calcula-
tions is then provided by the application of the
normal mode analysis and Fourier transform in-
fra red (FTIR) spectroscopy which are well es-
tablished techniques and are being used for
variety of other applications [9–13]. For this
purpose at least one compound in the series of
analogs is first selected which can be conve-
niently studied by X-ray diffraction for the de-
termination of its conformation. Its FTIR
spectrum is recorded and the normal mode anal-
ysis is carried out using its X-ray determined
conformation to establish the force field con-
stants which give the best agreement between
the spectra and the calculated frequencies. These
force field constants are utilized in the normal
mode analysis of the analog using its geometry
calculated from the molecular orbital method.
This is reasonable because the force field con-
stants are invariant from one analog to the
other, as there is not much change in the basic
structural environment. If the theoretical fre-
quencies of the analogs agree with their FTIR
spectra then it is concluded that the calculated
geometry is correct, otherwise it is again deter-
mined using a different conformation of the
molecule. These experimentally supported con-
The compound 1-[(3-methylphenyl)piperazin-1-
yl]-3-[thio(4-acetamidophenyl]propane (3) was
synthesized essentially by the reported method
[1] starting from 4-acetamidothiophenol (1),
which on condensation with 1-bromo-3-chloro-
propane yielded the key intermediate chloro-
propyl derivative (2). This on reaction with
3-methylphenyl piperazin in the presence of
sodium carbonate and sodium iodide in DMF
afforded the title compound (3) as shown in
Scheme 1.
The FTIR spectra in KBr and in dilute
CHCl3 solution were recorded on the Impact
400 spectrophotometer, Nicolet, having a resolu-
tion of 1 cm−1, using interferometer dispersing
KBr beam splitter and having noise level equal
to RMS 7.1. The X-ray data used for the calcu-
lations were taken from Carpy et al. [7]. The
well-known Wilson’s G-F matrix method [14]
with Urey–Bradley force field has been used to
evaluate the normal mode frequencies of vibra-
tion. These are given by the eigen values of the
secular equation
GFL=uL
(1)
as
u=4y2c2f 2
(2)
The potential is represented as

R.B. Singh et al. / Spectrochimica Acta Part A 56 (2000) 1267–1275
1269
1
2
figure obtained from the X-ray diffraction [7]. The
important calculated normal mode frequencies,
along with the observed frequencies in the FTIR
spectra in KBr, their assignments and percentage
PED are tabulated in Table 1. The complete table
of all the calculated frequencies is provided as
supplementary material. The assignments are based
on the concept of group frequencies and band
intensities. The internal co-ordinates and corre-
sponding force constants are given in Table 2.
The NꢀH mode vibrations along with amide I
and II band-positions and their intensities are used
with reasonable certainty to characterize the cis- or
trans-configuration and hydrogen-bonding effects
in the secondary amide group. A very strong band
at 3307 cm−1 is assigned to NꢀH stretch of the
amide group in the solid state. The strong intensity
can be attributed to the Fermi resonance of NꢀH
stretch with the overtone of amide I band (1659
cm−1). This band is suggestive of the ꢀNꢀH…O=
C rather than the ꢀNꢀH…Nꢀ linkage involvement,
i.e. N-mono-substituted amide exists mainly with
NꢀH and C=O in trans- rather than cis-configu-
ration. The X-ray data also supports this.
!
"
6=% K% 6jk(D6jk)+ Kjk(D6jk)2
jk
j,k
1
2
!
"
+ % H% r rjk(DFijk)2+ Hijkrijrjk(DFijk)2
+
ijk ij
i, j,k
1
2
!
"
% F% qik(Dqik)+ Fikqik(Dqik)2 +% Kjꢀ(Dꢀj)2
ik
i, j
j
+% K~j (D~j)2
(3)
j
where Dwjk, DFijk, Dꢀj, D~j are the internal co-ordi-
nates corresponding to bond stretch, angle bend,
out of plane deformation and torsion respectively
and q represents non-bonded nearest neighbor
interactions. The potential energy distribution
(PED) in the jth internal co-ordinate for the ith
normal mode is given by
L*LjiFji
ji
(PED)ij=
(4)
ui
The estimates of the force constants for the force
field were taken from the literature [14,15] and
subsequently refined to match the observed spectra.
In addition to the above main absorption band
of NꢀH stretching vibration we get two associated
NꢀH bands of medium intensity at 3155 and 3090
cm−1. These bands are also observed in the spectra
of polypeptides and proteins where their relative
intensities vary with the transition of protein from
alpha to beta folding.
3. Results and discussion
The FTIR spectra of the title compound in KBr
and in dilute CHCl3 solution are shown in Figs.
1–3. The conformer structure diagram of the
molecule is shown in Fig. 4. This is in line with the
Scheme 1.

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R.B. Singh et al. / Spectrochimica Acta Part A 56 (2000) 1267–1275
Fig. 1. The FTIR spectrum of the title compound in KBr: (400–4000 cm−1).
Fig. 2. The finger print region spectrum of the title compound in KBr: (700–1700 cm−1).

R.B. Singh et al. / Spectrochimica Acta Part A 56 (2000) 1267–1275
1271
Fig. 3. The FTIR spectrum of the title compound in dilute CHCl3 solution: (400–4000 cm−1).
The above three bands disappear in dilute
CHCl3 solution and are replaced by a strong band
at 3436 cm−1 for NꢀH stretching. This suggests
the intra-molecular hydrogen bonding effect to be
giving rise to them in the solid phase. The intensity
to the band at 3155 cm−1 may have been provided
by the overtone (2×amide III+amide IV) and to
the band at 3090cm−1 by (2×amide II).
The strongest and most characteristic bands of
the secondary amides, i.e. amide I and amide II lie
between 1500 and 1700 cm−1 [16]. The amide I
band occurs at 1686 cm−1 in the solution phase and
at 1658 cm−1 in the solid phase. This may again
suggest to the intra-molecular hydrogen bonding in
the solid phase as it affects the resonance between
C=O and CꢀN stretching causing decrease in the
frequency. The frequency of 1686 cm−1 corre-
sponds to Hammett | constant equal to 0.23 and
variation in intensity also follows the Thompson
and Jameson correlation [17].
The strong band at 1534 cm−1 in the solid phase
is assigned to the amide II vibration (NꢀH bend-
ing+aryl CꢀN and amide CꢀN stretch). X-ray
data shows decreased CꢀN bond lengths of
Fig. 4. The structure of the title compound.

1272
R.B. Singh et al. / Spectrochimica Acta Part A 56 (2000) 1267–1275
Table 1
Normal mode frequencies and their assignments
Frequencies (in cm−1
)
Assignments (PED is given in % within brackets and the groups are given within braces)
Calculation
Observed
3307
3086
3084
3083
3082
3041
3037
3035
3034
2953
2917
2871
2868
2844
2841
2840
2836
2827
2822
2821
2820
2819
1659
1600
1599
1535
1501
3307
3084
3084
3084
3084
3039
3039
3039
3039
2953
2926
2872
2872
2820
2820
2820
2820
2820
2820
2820
2820
2820
1659
1600
1600
1534
1494
1494
1494
1446
1446
1446
1446
1433
1393
1393
1372
1349
1318
1295
1290
1261
1249
1185
1185
1128
1087
1066
1066
1033
n(NꢀH) [100]
n(CꢀH) [100]
n(CꢀH) [100] {phenyl 1}
–
n(CꢀH) [95]
n(CꢀH) [100]
n(CꢀH) [100]
n(CꢀH) [91] {phenyl 2}
n(CꢀH) [98]
n(CꢀH) [99]
n(CꢀH) [100] {phenyl 2ꢀCH3 asymmetrical}
n(CꢀH) [96] {OꢁCꢀCH3 asymmetrical}
n(CꢀH) [100] {SꢀCH2 symmetrical}
–
–
n(CꢀH) [100] {OꢁCꢀCH3 symmetrical}
n(CꢀH) [87] {piperazin-CH2 symmetrical}
n(CꢀH) [97] {piperazin-CH2 symmetrical}
n(CꢀH) [96] {piperazin-CH2 symmetrical}
n(CꢀH) [98] {piperazin-CH2 symmetrical}
n(CꢀH) [100] {piperazin-CH2 symmetrical}
n(CꢀH) [89] {piperazin-CH2 symmetrical}
n(CꢀH) [100] {piperazin-CH2 symmetrical}
n(CꢀH) [100] {piperazin-CH2 symmetrical}
n(CꢀH) [100] {piperazin-CH2 symmetrical}
Amide I (n(CꢁO) [67], n(CꢁN) [23])
n(CꢀC) [71] f(CꢀCꢀH) [24] {phenyl 2}
–
–
n(CꢀC) [64] f(CꢀCꢀH) [34] {phenyl 1}
Amide II (f(CꢀNꢀH) [48], n(CꢀN) [17])
n(CꢀC) [37] f(CꢀCꢀH) [32], {phenyl 2}
–
f(HꢀCꢀH) [20] {phenyl 2ꢀCH3}
–
1498
1451
1444
1442
1441
1433
1398
1389
1373
1356
1314
1299
1286
1262
1246
1185
1184
1122
1082
1066
1046
1029
n(CꢀC) [33] f(CꢀCꢀH) [33] {phenyl 1} f(CꢀNꢀH) [21] {amide}
–
f(HꢀCꢀH) [72] f(CꢀCꢀH) [11] {Phenyl 2ꢀCH3 symmetrical}
–
f(HꢀCꢀH) [54] {aliphatic}; CH2 scissoring
f(HꢀCꢀH) [52]; f(CꢀCꢀH) [20] {piperazin};CH2 scissoring
f(HꢀCꢀH) [60] f(CꢀCꢀH) [11] {piperazin};CH2 scissoring
f(HꢀCꢀH) [48] f(CꢀCꢀH) [17] {aliphatic}; CH2 scissoring
f(HꢀCꢀH) [37] f(NꢀCꢀH) [14] {piperazin}
n(CꢀN) [10], f(HꢀCꢀH) [24] {aliphatic} f(HꢀCꢀH) [14] {piperazin}
n(CꢀC)+n(CꢀN) [21] {piperazin} f(HꢀCꢀH) [20] {aliphatic}
f(HꢀCꢀH) [65] f(CꢀCꢀH) [12] {Phenyl 2-H3 symmetrical}
(n(CꢀC)+n(CꢀN)) [23], f(CꢀCꢀH) [30] {Piperazin}, n(aryl-N) [24]
f(CꢀCꢀH) [30] f(HꢀCꢀH) [69] CH2 wagging
f(CꢀCꢀH) [24] f(HꢀCꢀH) [42] CH2 wagging
Amide III (n(CꢀC) [38] n(CꢀN) [24] f(CꢀNꢀH) [16] )
f(SꢀCꢀH) [31] f(CꢀCꢀH) [17] n(CꢀC) [28] {aliphatic}
n(CꢀN) [11] {Aryl-N} f(CꢀCꢀH) [27] {piperazin} f(CꢀCꢀH) [23] {phenyl 2}
n(CꢀC)[12] f(CꢀCꢀH)[34] {Phenyl 1} n(CꢀN) [23] {Aryl-Amide}
(n(CꢀC)+ n(CꢀN)) [15] (f(NꢀCꢀH)+f(CꢀCꢀH) [46] {Piperazin}
n(CꢀN) [12] f(NꢀCꢀH) [22] {Piperazin}
n(CꢀC) [5] f(CꢀCꢀH) [50] {Piperazin}
n(CꢀC)+ n(CꢀN)+ f(CꢀNꢀH) [90] {Piperazin Ring Vibrations}
n(CꢀC) [29] f(CꢀCꢀH) [35] {Aliphatic}
–
–
–

R.B. Singh et al. / Spectrochimica Acta Part A 56 (2000) 1267–1275
1273
Table 1 (Continued)
Normal mode frequencies and their assignments
Frequencies (in cm−1
)
Assignments (PED is given in % within brackets and the groups are given within braces)
Calculation
Observed
1013
945
934
930
923
1011
954
936
936
914
n(CꢀC) [38] f(CꢀCꢀH) [20] {Phenyl 2}
–
n(CꢀN) [25] (f(NꢀCꢀH)+f(CꢀCꢀH)) [30] {Piperazin}
n(CꢀC) [37] f(CꢀCꢀH) [48] {Phenyl 2}
–
v(CꢀH) [43] {2 Adj H} t(CꢀC) [48]
–
–
(n(CꢀC)+n(CꢀC)) [18] {Piperazin} n(Aryl-N) [7] n(CꢀC) [32] {Phenyl 2} f(CꢀCꢀH) [6] f(HꢀCꢀH)
–
[7] {Phenyl-CH3}
865
835
767
862
833
768
v(CꢀH) [48] {Lone H}, n(SꢀC) [12] n(NꢀC) [12] {Aliphatic}
v(CꢀH) [69] {2 Adj H} t(CꢀC) [21]
–
–
Amide V {n(CꢀC) [31] {Phenyl 1} n(CꢀN) {Phenyl-Amide} [10] n(CꢀN) {Me-Amide} [14] v(NꢀH)
–
[40]}
735
691
689
555
514
479
460
436
403
738
702
690
554
505
480
465
432
405
v(CꢀH) [70] {3 Adj H} t(CꢀC) [27]
–
–
f(CꢀCꢀH) [60] {Phenyl 2} n(CꢀC) [38]
–
n(CꢀC) [23] f(CꢀCꢀC) [15] {Phenyl 2} f(CꢀCꢀN)[13] {Piperazin}
–
–
f(CꢀCꢀC) [60] n(CꢀC) [08] {Phenyl 1}
f(CꢀCꢀC) [15] {Aliphatic} f(CꢀCꢀN) [23] (t(CꢀC)+ t(CꢀN)) [25] {Piperazin}
f(CꢀCꢀC) [38] n(CꢀC) [17] {Phenyl 2-CH3}
–
f(CꢀNꢀC) [11] {Piperazin} v(CꢀH) {2 Adj H} [11] t(CꢀC) [19] {Phenyl 1}
–
–
–
f(CꢀCꢀN) [15] (t(CꢀC)+t(CꢀN)) [28] {Piperazin}
f(SꢀCꢀC)[10] {Aliphatic} t(CꢀC) [18] f(CꢀCꢀC) [12] {Phenyl 2}
–
,
the order of 1.34 A which are shorter than the
trum has been assigned to the CꢀH stretching
,
usual single CꢀN bond length of 1.38 A. This may
vibration of 1,4 di-substituted benzene (hereafter
be ascribed to the increased bond orders of the
CꢀN bonds due to resonance stiffening. These
increased bond orders also contribute to the de-
crease in the frequency of NꢀH bending, which is
caused by the increased effective mass of the
hydrogen due to the effect of the hydrogen bond-
ing. In the solution phase, this band shifts to 1560
referred to as phenyl 1). The difference in indi-
–
vidual bond lengths in this ring is similar to that
of polycyclic structures. These differences are ne
cessarily reflected in the FTIR spectrum. These
along with the presence of unoxidized sulfur in
this ring are suggestive of a very weak absorption
band, but the interaction of this band position
with the associated NꢀH vibration of bonded
amide in the same region may be the reason for
the increased intensity of the band. The band at
1600 cm−1 is assigned to quadrant stretching of
benzene rings.
cm−1
.
The medium intensity band at 1261 cm−1 is
assigned to Amide III and has major contribution
from CꢀC (O=CꢀCH3) stretching with lesser
contributions of CꢀN stretch and CꢀNꢀH in plane
bending.
The out-of-plane bending vibrations of the hy-
drogen atoms in the two phenyl rings are compli-
cated by the heavy substitutions, viz. unoxidized
sulfur and acetamide at 1,4 positions in one
The strong absorption band at 596 cm−1 is
assigned as amide VI vibration band. It seems
that inductive and resonance effects play in tune
to shift the frequency to higher side and to in-
crease the intensity of the band.
(phenyl 1) and the piperazin ring and methyl
–
group at 1,3 position in the other (hereafter re-
ferred to as phenyl 2). The situation becomes
–
3.1. Benzene ring 6ibrations
more so due to the presence of piperazin ring
vibrations in the same region.
The band at 3090 cm−1 in the solid KBr spec
A strong band at 820 cm−1 and a medium

1274
R.B. Singh et al. / Spectrochimica Acta Part A 56 (2000) 1267–1275
f(HꢀCꢀH) Piperazin ring
0.315(0.200)
0.350(0.240)
Table 2
Internal co-ordinates and their force constantsa
f(HꢀCꢀH) CH2 attached to
phenyl
2
–
f(SꢀCꢀH)
0.423(0.210)
0.440(0.250)
0.425(0.230)
0.120
0.260
0.500
0.160
0.110
0.070
0.040
0.060
0.080
0.070
0.085
0.072
0.040
0.041
0.039
Internal co-ordinates
Force constants*
(×105 dynes/cm)
f(CꢀNꢀC) Phenyl 1-NꢀC
–
f(CꢀCꢀN) Amide
v(CꢀH)
v(NꢀH)
v(CꢁO)
v(CꢀH)
v(CꢀH)
t(CꢀC)
t(CꢀN)
t(CꢀC)
t(CꢀS)
t(SꢀC)
t(CꢀC)
t(CꢀN)
t(CꢀC)
t(CꢀN)
t(CꢀC)
t(CꢀC)
Phenyl 1
n(CꢀC)
n(CꢀN)
n(CꢀS)
n(CꢀS)
n(CꢀC)
n(CꢀC)
n(CꢀN)
n(CꢀN)
n(CꢀC)
n(CꢀN)
n(CꢀC)
n(CꢀC)
n(C=O)
n(CꢀC)
n(CꢀN)
n(CꢀH)
n(CꢀH)
n(CꢀH)
n(CꢀH)
n(CꢀH)
n(CꢀH)
Phenyl
Phenyl 1-amide
1
5.060
3.830
3.680
3.520
3.850
3.900
3.590
3.620
3.650
3.730
4.950
4.750
8.840
4.340
3.840
4.930
4.310
4.280
4.090
4.770
4.300
–
–
–
Phenyl-sulfur
Aliphatic-sulfur
CH2 adjacent to S
Aliphatic
Aliphatic-piperazin
Piperazin
(Lone H) phenyl
2
–
Phenyl
Phenyl
Phenyl 1-amide
OꢁCꢀCH3
Phenyl 1-S
2
1
–
–
–
Piperazin
Aryl-N
Phenyl
Phenyl-CH3
–
SꢀCH2
Aliphatic
Piperazin
Piperazin
Aryl-N
2
–
O=CꢀCH3
Amide
Phenyl
Phenyl
Phenyl 2ꢀCH3
2
–
–
0.040
1
–
CH2 adjacent to S
Aliphatic CH2
Piperazin CH2
Phenyl
CH3 attached to
phenyl
2
–
band at 835 cm−1 are assigned to out-of-plane
vibration of two adjacent hydrogen atoms in 1,4
different bond orders of benzene CꢀC bonds.
This is also evident from the X-ray data with
the standard deviation approximately equal to
2
–
n(NꢀH)
n(CꢀH)
f(CꢀCꢀH) Phenyl
f(CꢀCꢀH) CH2 adjacent to S
f(CꢀCꢀH) Aliphatic CH2
f(NꢀCꢀH) CH2-piperazine
f(CꢀCꢀH) CH2-piperazine
5.800
4.200
O=CꢀCH3
1
0.355(0.230)
0.368(0.170)
0.370(0.210)
0.369(0.200)
0.371(0.180)
0.360(0.230)
0.394(0.190)
–
,
,
0.02 A over the mean value of 1.39 A of the
CꢀC bond length.
The band at 779 cm−1 is assigned to the
wagging of the three adjacent hydrogen atoms
present in 1,3 di-substituted phenyl ring, and
that at 862 cm−1 is assigned to the wagging
vibration of the isolated hydrogen atom. The
intensity of the latter is rather weak due to the
presence of piperazin ring adjacent to this lone
hydrogen atom.
f(CꢀCꢀH) Phenyl
f(CꢀCꢀH) CH3 attached to
2
–
phenyl
2
1
–
–
–
–
–
f(CꢀCꢀC) Phenyl
0.485(0.350)
0.580(0.320)
0.753(0.400)
0.760(0.500)
0.750(0.400)
0.513(0.250)
0.510(0.180)
0.490(0.150)
0.491(0.230)
0.490(0.250)
0.492(0.350)
0.493(0.260)
0.570(0.260)
0.569(0.270)
0.460(0.240)
0.419(0.240)
0.420(0.240)
f(CꢀCꢀN) Phenyl 1-amide
f(CꢀCꢀS) Phenyl 1-sulfur
f(CꢀSꢀC) Phenyl 1-thio-CH2
f(CꢀCꢀS) Aliphatic-sulfur
f(CꢀCꢀC) Aliphatic chain
f(CꢀNꢀC) Aliphatic-piperazin
f(CꢀCꢀN) Piperazin
The strong absorption band at 1318 cm−1 is
di-substituted benzene. The presence of two
bands may be ascribed to the charge redistribu-
tion, giving rise to assigned to aryl-N linkage
vibration. There is a striking similarity of this
band with the C=O and CꢀC vibrations where
either the compound is cyclic or one of the car-
bon atoms has aromatic character. The overlap-
ping of expected piperazin ring vibration in this
characteristic band is evident in the normal
mode calculations.
f(CꢀNꢀC) Piperazin
f(NꢀCꢀC) Piperazin-phenyl
2
–
f(CꢀCꢀC) Phenyl
f(CꢀCꢀC) Phenyl-CH3
f(NꢀCꢁO)
f(CꢀCꢁO)
f(CꢀCꢀH) (OꢁCꢀCH3)
f(CꢀNꢀH) (OꢁCꢀNꢀH)
2
–
f(CꢀNꢀH) (Phenyl 1-NꢀH)
–
f(HꢀCꢀH) CH3 attached to CꢁO 0.300(0.220)
f(HꢀCꢀH) Aliphatic CH2
0.320(0.210)

R.B. Singh et al. / Spectrochimica Acta Part A 56 (2000) 1267–1275
1275
1087 cm−1 have previously also been shown to
confirm the presence of tertiary amines (cyclic or
non-cyclic) along with the presence of CH3 or
CH2 group conjugated by a double bond in the
molecule.
3.2. Piperazin ring 6ibrations
The strong bands at 1128 and 1087 cm−1 are
assigned to the asymmetrical and symmetrical
CꢀN stretching vibrations in the heterocyclic
piperazin ring system. This is the same region in
which CꢀN vibrations in the non-cyclic tertiary
amines have their absorption bands. The CꢀC and
the CꢀN bond stretches couple with each other in
this favorable environment. The strong absorp-
tion band at 1446 cm−1 is assigned to the CH2
deformation frequency. This band shows the ab-
sence of ring strain in the chair conformation of
the piperazin ring. The band at 1295 cm−1 is
assigned to the CH2 wagging vibration. This band
along with the band at 1446 cm−1 are characteris-
tic of the piperazin or dioxane derivative six-mem-
bered ring. These bands are useful for the
detection of the ring strain, as any non-staggering
of the ring bonds would have increased the fre-
quencies of these two bands. The staggered chain
conformation is evident from the X-ray data. The
small lowering of the frequency of the band from
aliphatic CH2 wagging frequency at 1304 cm−1 is
attributed to the presence of the N atom in the
heterocyclic ring. This is well distinguished from
Acknowledgements
The authors are grateful for financial assistance
to the CSIR, India under whose project this work
was carried out. They are also thankful to the
CDRI, Lucknow and the University of Lucknow
for the facilities provided. RBS is grateful to
UGC, India for SRF.
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SꢀCH2 wagging frequency of 1249 cm−1
.
The band at 954 cm−1 is assigned to the sym-
metrical ring vibration of piperazin. The expected
contribution of other CꢀC linkages in this absorp-
tion band is shown by the calculations. The inter-
action of the CꢀCꢀH and NꢀCꢀH in-plane
bending due to the motion of the C atoms is also
evident.
The intense band at 2818 cm−1 is characteristi-
cally absorbed in the symmetrical CH2 stretching
of the group adjacent to the N atom. The large
intensity is attributed to the presence of a large
number of similar CH2 groups and to the Fermi
resonance with the additive bending vibration of
CH3 group present in the vicinity of the carbonyl
group (1446 cm−1+1371 cm−1). This vibration
along with ring breathing vibrations at 1128 and
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