Experimental and DFT study on pyrrole tosylhydrazones

Article abstract of DOI:10.1016/j.molstruc.2014.10.046

Two pyrrole tosylhydrazones, 1H-pyrrole-2-tosylhydrazone (PT) and ethyl 3,5-dimethyl-4-(1-(2-tosylhydrazono)ethyl)-1H-pyrrole-2-carboxylate (EDTEPC) have been synthesized and characterized by various spectroscopic techniques. All calculations have been pe

Full text of DOI:10.1016/j.molstruc.2014.10.046

Journal of Molecular Structure 1081 (2015) 543–554
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Experimental and DFT study on pyrrole tosylhydrazones
⇑
R.N. Singh , Poonam Rawat, Divya Verma, Shailendra Kumar Bharti
Department of Chemistry, University of Lucknow, Lucknow 226007, UP, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
ꢀ
FT-IR spectra of PT and EDTEPC were
recorded and compared with the
theoretical results.
The feasibility of the reaction has
been checked with the help of
electronic descriptors.
The calculated first
hyperpolarizability (b0 = 6.50/
8.38 ꢁ 10ꢂ30) of PT and EDTEPC.
Electronic transitions and chemical
shifts have been also calculated.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 August 2014
Received in revised form 19 October 2014
Accepted 20 October 2014
Available online 1 November 2014
Two pyrrole tosylhydrazones, 1H-pyrrole-2-tosylhydrazone (PT) and ethyl 3,5-dimethyl-4-(1-(2-
tosylhydrazono)ethyl)-1H-pyrrole-2-carboxylate (EDTEPC) have been synthesized and characterized by
various spectroscopic techniques. All calculations have been performed using B3LYP functional and
6-31G(d,p) basis set. The result of hydrogen bonding is obvious in 1H NMR and FT-IR due to down field
chemical shift and vibrational red shift to pyrrole NAH proton, respectively. The red shift in both the
proton donor (pyrrole NAH) and proton acceptor (S@O) group designates presence of intermolecular
classical hydrogen bonding NAHꢃ ꢃ ꢃO. The binding energy of dimer formation is calculated as 13.12,
14.12 kcal/mol, after correction in basis set superposition error (BSSE). Topological parameters indicate
Keywords:
B3LYP
FT-IR
the weaker interactions presents in the molecules. The global electrophilicity index (
x = 2.54, 2.28 eV)
Red shift
shows that PT and EDTEPC molecules are strong electrophile. The local reactivity descriptors analyses
are performed to determine the reactive sites within the PT and EDTEPC. Computed first hyperpolarizability
(b0 = 6.50/8.38 ꢁ 10ꢂ30 esu) of PT and EDTEPC indicates non-linear optical (NLO) response of the molecules.
Ó 2014 Elsevier B.V. All rights reserved.
Dimer
First hyperpolarizability
Introduction
anti-inflammatory, analgesic [5,6] and anti-pyretic [7–9]. They
are versatile starting materials for the synthesis of a variety of N,
Hydrazones have triatomic >C@NAN< linkage, containing two
connected nitrogen atoms of different nature and a C@N double
bond that is conjugated with a lone electron pair of the terminal
nitrogen atom. These structural fragments are mainly responsible
for the physical and chemical properties of hydrazones [1].
Hydrazones possess an azomethine proton ACH@NANHA and
constitute an important class of compounds for different types of
biological activity such as antibacterial [2,3], antidepressant [4],
O or S containing heterocyclic compounds such as oxadiazolines,
thiazolidinones, triazolines, and various types of other organic
compounds [10–21].
Sulfonylhydrazide and sulfonylsemicarbazide derivatives
exhibit a variety of bacteriostatic activity and also are important
compounds as blowing agents in cellular rubber and plastics. The
aromatic sulfonylhydrazides are particularly useful in the produc-
tion of azo dyes [22]. Due to the presence of a sulfonamide proton
(ANHASO2A) these compounds have strong coordinating ability
towards metal ions [23]. As per literature survey synthesis and
brief spectral analysis of 1H-pyrrole-2-tosylhydrazone was
reported by Richard et al. in 1978 [24].
⇑
Corresponding author. Tel.: +91 9451308205.
E-mail address: rnsvk.chemistry@gmail.com (R.N. Singh).
http://dx.doi.org/10.1016/j.molstruc.2014.10.046
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

544
R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
Hydrogen bonds are also of versatile importance in fields of
Synthesis of ethyl 3,5-dimethyl-4-(1-(2-tosylhydrazono)ethyl)-1H-
pyrrole-2-carboxylate (EDTEPC)
chemistry and bio-chemistry, which governs chemical reactions,
supramolecular structures, molecular assemblies and life pro-
cesses. The quantum chemical calculation is powerful approach
for study of different aspects of compounds [25,26].
The solution of ethyl 4-acetyl-3,5-dimetyl-1H-pyrrole-2-car-
boxylate [26] (0.200 g, 0.9564 mmol) in 20 ml methanol was added
dropwise to a stirred solution of para-toluene sulphonyl-hydrazide
(0.1779 g, 0.9564 mmol) dissolved in 20 ml methanol. Two drops
of polyphosphoric acid were added as a catalyst. Reaction mixture
was refluxed for 36 h. A white color precipitate appeared. The pre-
cipitate was filtered off, washed with methanol and dried in air.
Yield: 65% Color: white, m.p. 210 °C; Anal. calcd. for C17H21N3O4S:
C 56.18%, H 5.82%, N 11.56%, obs.: C 56.02%, H 5.72%, N 11.44%. MS
(m/z): calcd.363.43, obs.: 364 [M+H]+.
In view of various significance of Pyrrole sulfonylhydrazone,
ethyl
3,5-dimethyl-4-(1-(2-tosylhydrazono)ethyl)-1H-pyrrole-
2-carboxylate (EDTEPC) has been synthesized. In this paper we
present the structural, spectral and quantum chemical study of
both PT and EDTEPC. The present investigation reveals the detailed
spectroscopic nature of PT and EDTEPC and contributes to the
understanding of the FT-IR spectra that these compounds contain
hydrogen bonding. With the help of Bader’s theory of ‘‘Atoms in
molecules’’ (AIM) nature and strength of bonding have been
revealed [27]. The theory of AIM efficiently describes H-bonding
and its concept without border. Information about the potential
energy distribution (PED) over the internal coordinates, conforma-
tions of the molecule together with complete analysis of geometry
and chemical reactivity help in understanding the structural and
spectral characteristics, have been studied. In particular, the inter-
est in these compound provides opportunity for synthesis of new
heterocyclic compounds, metal and organometallic complexes that
may have considerable pharmacological activities and material
applications. Therefore, the PT and EDTEPC was synthesized and
characterized. In this paper we report the synthesis, detailed
molecular structure, spectroscopic analysis and chemical reactivity
of PT and EDTEPC using experimental and quantum chemical
calculations.
Results and discussion
Molecular structures, dimerization and Quantum Theory of Atoms in
Molecules (QTAIM) analysis
Scheme 1 shows the formation of PT and EDTEPC compound.
Selected optimized geometrical parameters of PT and EDTEPC, cal-
culated at B3LYP/6-31G(d,p) are listed in Supplementary Table S1a
and Table S1b. The optimized geometries of PT and EDTEPC are
shown in Fig. 1. The studied molecules possess C1 symmetry. In
both of the studied compounds tosylhydrazonomethyl group in
PT and EDTEPC are away from the plain by N26AN1AS3AC6,
N14AN15AS16AC19 torsion angle of 59.93°, 77.55° respectively.
The conformation of the NANASAO linkage is anti, with torsion
angles of 169.21°, ꢂ37.77°, which giving a folded appearance in
both PT and EDTEPC molecules, respectively. The asymmetry of
NAC bonds in the pyrrole has been observed in EDTEPC molecule
due to the presence of the ethoxy group present at C2 of pyrrole
ring. The molecular structure of PT and EDTEPC shows E-configura-
tion of the hydrazone double bond. The presence of a methylene
and sulphonamide frame between the pyrrole and benzene moie-
ties allows the benzene ring and the pyrrole system to be some-
what parallel with respect to each other, so that the molecule
adopts a U-shaped spatial conformation. The crystal structures of
synthesized compounds have not been reported but geometrical
parameters are taken for optimization from the crystal structure
of 4-ethyl benzene sulfonylhydrazones [31]. Optimized geometry
for monomer and dimer of PT and EDTEPC are shown in Fig. 2,
respectively. Both molecules exist in the form of dimer. The dimer
of EDTEPC form eight member ring, due to the intermolecular clas-
sical hydrogen bonding (NAHꢃ ꢃ ꢃO) both proton donor (NAH bond)
and proton acceptor (C@O bond) are elongated by 1.0204 from
1.0103 Å(monomer) and 1.232 from 1.224 Å(monomer), respec-
tively. EDTEPC also form dimer through hydrazone NAH and
S@O group. The dimer of EDTEPC through hydrazone NAH and
S@O group is higher in energy than EDTEPC dimer through NAH
and C@O group. Total energy for ground state lower energy dimer
of EDTEPC is calculated as ꢂ3126.18000 a.u. The PT forms dimer
through hydrazone NAH and S@O group. The total energy of PT
is calculated as ꢂ2355.84276 a.u. The elongation of 1.0314 Å
(1.0234 Å monomer), 1.464 Å (1.478 Å monomer) in bond length
of hydrazone NAH and tosyl S@O group, respectively, in PT dimer.
The calculated binding energy of EDTEPC and PT dimer formation
are found as 13.12, 14.12 kcal/mol, respectively, after correction
in basis set superposition error (BSSE) via standard counterpoise
method [32].
Experimental details and quantum chemical calculations
The Mass spectrum of PT and EDTEPC were recorded on
JEOL-Acc TDF JMS-T100LC, Accu TOF mass spectrometer. The 1H
NMR spectra of PT and EDTEPC were recorded in DMSO-d6 on
Bruker DRX-300 spectrometer using TMS as an internal reference.
The FT-IR-spectra of PT and EDTEPC were recorded in KBr medium
on a Bruker-spectrometer. The UV-Visible absorption spectra of PT
and EDTEPC, (1 ꢁ 10ꢂ5 M in DMSO) were recorded on ELICO SL-164
spectrophotometer. All the quantum chemical calculations have
been carried out with Gaussian 09 program package [28] to predict
the molecular structure, energies of the optimized geometry, 1H
NMR chemical shifts and vibrational wavenumbers using DFT level
of theory, B3LYP functional and 6-31G(d,p) as basis set. The
optimized geometrical parameters are used in the vibrational
wavenumbers calculation to characterize all stationary points as
minima and their harmonic vibrational wavenumbers are positive.
Potential energy distribution (PED) along internal coordinates is
calculated by Gar2ped software [29]. Molecular graph were
computed using AIMALL software [30]. To estimate the enthalpy
(H) and Gibbs free energy (G) values, thermal corrections to the
enthalpy and Gibbs free energy are added to the calculated total
energies.
Preparation of 1H-pyrrole-2-tosylhydrazone (PT)
A
solution of 4-methylbenzenesulfonylhydrazide (0.2134 g,
1.1464 mmol) in 15 ml methanol and 0.01 ml of conc. HCl as
catalyst was added drop-wise with stirring in solution of
2-formyl-1H-pyrrole (0.250 g, 1.1464 mmol) in 10 ml methanol
at room temperature. After stirring for 12 h, the precipitate was
obtained. The precipitate was filtered by vacuum filtration, washed
with methanol and dried in air, afforded (0.200 g, 45.17%) of PT, as
orange color solid. m.p. 169–173 °C; Anal. calcd. for C12H13N3O2S: C
54.74%, H 4.98%, N 15.96%, obs.: C 54.02%, H 4.72%, N 15.44%. MS
(m/z): calcd. 263.07, obs. 264 [M+H]+.
The calculated thermodynamic parameters for dimerization
reaction at 25 °C are listed in Table 1. For dimerization reaction,
the calculated negative value of Gibbs free energy change (DG)
show that the reaction is spontaneous thermodynamically. At
room temperature, the equilibrium constant (Keq) for dimerization

R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
545
Scheme 1. Route representing synthesis of pyrrole tosylhydrazones using reactants (1, 2 and 5), product (3: PTand 6: EDTEPC) and byproduct water (4).
PT
Dimer PT
EDTEPC
Fig. 1. Optimized geometry for PT and EDTEPC.
reaction of PT and EDTEPC are calculated to be 25.28 and 2.45 i.e.
Keq ꢄ 1. Therefore, reactions are more favored in the forward
direction and confirm the formation of dimer at room temperature.
Molecular graph of dimer using AIM program at B3LYP/
6-31G(d,p) level is shown in Fig. 3 for PT and EDTEPC molecules.
Topological as well as geometrical parameters for bonds of interact-
ing atoms in dimer of PT and EDTEPC are given in Table 2. The PT
dimer shows two interactions. The interactions N1AH27ꢃ ꢃ ꢃO35A
S34/N32AH33ꢃ ꢃ ꢃO4AS3 in PT is medium classical intermolecular
Dimer EDTEPC
Fig. 2. Optimized geometry for dimer of PT and EDTEPC.
hydrogen bonds due to (
2qBCP) > 0 and HBCP < 0 in EDTEPC
r
N1AH27ꢃ ꢃ ꢃO59AC55/N50AH76ꢃ ꢃ ꢃO10-C6 is weak classical inter-
molecular hydrogen bonds due to (
r
2qBCP) > 0 and HBCP > 0. The
NMR and UV–Vis spectroscopy
hydrogen bond energy of N1AH2ꢃꢃꢃO35-S34/N32AH33ꢃ ꢃ ꢃO4AS3 in
PT found to be ꢂ6.554 kcal/mol and in EDTEPC molecule
1H NMR chemical shifts of PT and EDTEPC are calculated using
GIAO method and IEFPCM model in DMSO-d6 as solvent are
listed in Table 3 and shown in Supplementary Figure S1(a) and
Figure S1(b), respectively. 1H NMR spectra of PT and EDTEPC show
the presence of singlet at 11.503, 11.396 ppm for NH protons of
N1AH27ꢃ ꢃ ꢃO59-C55/N50AH76ꢃ ꢃ ꢃO10AC6
is
calculated
as
ꢂ6.2158 kcal/mol. The energy of HAH interaction is calculated as
ꢂ0.3291, ꢂ0.1662 kcal/mol in PT and EDTEPC respectively. The
other weaker interactions found in EDTEPC are shown in Table 2.

546
R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
Table 1
Calculated Enthalpy (H), Gibbs free energy (G) and Entropy (S) of PT and EDTEPC (Monomer, Dimer) and their change for Dimerization, at 25 °C.
Thermodynamic parameters
2xMonomer
Dimer
Dimerization reaction
Keq
PT
H (a.u.)
G (a.u.)
S (cal/mol K)
ꢂ2355.30569
ꢂ2355.436556
275.432
ꢂ2355.325298
ꢂ2355.439603
240.575
ꢂ0.01961
ꢂ0.00305
ꢂ34.857
25.28
EDTEPC
H (a.u.)
G (a.u.)
S (cal/mol K)
ꢂ3125.311456
ꢂ3125.492254
380.526
ꢂ3125.331257
ꢂ3125.493103
340.635
ꢂ0.019801
ꢂ0.000849
ꢂ39.891
2.4524
PT
EDTEPC
Fig. 3. Molecular graph for dimer of PT and EDTEPC: bond critical points (small red spheres), ring critical points (small yellow sphere), bond paths (pink lines) using AIM
program. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
pyrrole. The broad singlet at d 10.172 ppm corresponding to NH pro-
ton of hydrazone (C@NNH) linkage in EDTEPC. The hydrazone NH
proton observed at 9.236 ppm in PT spectrum. A quartet at d
4.158–4.228 ppm, and a triplet at d 1.234–1.281 ppm confirm the
presence of methylene and methyl of the ester group in EDTEPC. A
singlet at d 2.101 ppm and 2.065 ppm of methyl groups at 3- and
5-position of pyrrole ring, respectively, in EDTEPC. A singlet at d
2.003 ppm corresponds to protons of methyl group directly attached

R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
547
Table 2
with the calculated values. In PT, CH@N proton is observed as a sin-
glet at 7.259 ppm. All the calculated chemical shifts corroborate
with the observed chemical shifts in EDTEPC and PT except pyrrolic
NH. The deshielding in the chemical shift of pyrrole NAH proton des-
ignates presence of intermolecular hydrogen-bonding.
Topological parameters for intramolecular interaction: electron density
(qBCP),
Laplacian of electron density (r2qBCP), electron kinetic energy density (GBCP), electron
potential energy density (VBCP), total electron energy density (HBCP), Hydrogen bond
energy (EHB) at bond critical point (BCP) of PT and EDTEPC.
Interactions qBCP
r
2qBCP GBCP
VBCP
HBCP
EHB
To obtain the nature of electronic transitions and absorption,
the UV–visible spectra of PT and EDTEPC have been studied by
TD/DFT method at same basis set. The calculated electronic transi-
tions of PT and EDTEPC are listed in Table 4 and shown in Fig. 4 and
molecular orbital plots in Fig. 5. In EDTEPC, the observed electronic
transitions of EDTEPC are observed at kmax = 265 nm, which corre-
lates well with calculated wavelength at 279 nm. In theoretical
UV–Vis spectrum of PT calculated at kmax = 283 nm, corroborate
well with the experimental wavelength at 300 nm. The observed
PT
H12ꢃ ꢃ ꢃH43
H2ꢃ ꢃ ꢃO35
O4ꢃ ꢃ ꢃH33
0.0027 0.0095
0.0277 0.0796
0.0277 0.0796
ꢂ0.0006 ꢂ0.0010 ꢂ0.0017 ꢂ0.3291
0.0004 ꢂ0.0208 ꢂ0.0204 ꢂ6.5540
0.0004 ꢂ0.0208 ꢂ0.0204 ꢂ6.5537
EDTEPC
O10AH76
H27AO59
H28AO59
O10AH77
C56AN63
C7AN14
0.0260 0.0833
0.0260 0.0832
0.0067 0.0244
0.0067 0.0245
0.0095 0.0356
0.0095 0.0356
0.0084 0.0349
0.0084 0.0349
0.0014 0.0048
0.0014 0.0047
0.0126 0.0460
0.0126 0.046
0.0203 ꢂ0.0198
0.0203 ꢂ0.0198
0.0052 ꢂ0.0043
0.0052 ꢂ0.0043
0.0072 ꢂ0.0056
0.0072 ꢂ0.0056
0.0005 ꢂ6.2158
0.0005 ꢂ6.2098
0.0009 ꢂ1.3460
0.0009 ꢂ1.3488
0.0016 ꢂ1.7717
0.0016 ꢂ1.7720
0.0020 ꢂ1.4759
0.0020 ꢂ1.4777
0.0003 ꢂ0.1662
0.0003 ꢂ0.1656
0.0012 ꢂ2.8112
0.0012 ꢂ2.8074
electronic transitions confirm the
p ?
p⁄ in nature.
C9AH47
0.006
ꢂ0.0047
C58AH96
H30AH43
H79AH92
O60AH81
O11AH32
0.0067 ꢂ0.0047
0.0008 ꢂ0.0005
0.0008 ꢂ0.0005
0.0102 ꢂ0.0089
0.0102 ꢂ0.0089
Vibrational assignments
The experimental and theoretical (selected) vibrational wave-
numbers of PT and EDTEPC, calculated at B3LYP/6-31G(d,p) method
and their assignments using PED are given in Tables 5a and 5b. The
observed wavenumbers are assigned by comparing the calculated
wavenumbers using potential energy distribution (PED) analysis
of the various vibrational modes. Comparisons between experi-
mental and theoretical IR spectra for PT and EDTEPC in the region
4000–400 cmꢂ1 are shown in Figs. 6a and 6b, respectively. In major-
ity of the normal modes vibrational wavenumbers are higher than
their experimental values. This discrepancies have been corrected
qBCP
,
r
2qBCP, GBCP, VBCP, HBCP in a.u. and EHB in (kcal/mol)
to carbon of hydrazone (C@NNH) linkage in EDTEPC spectrum. The
CH protons of benzene ring are observed at two doublet corresponds
to four CH protons of benzene ring. The observed value of two CH
protons of benzene ring as a doublet at d 7.735–7.762 ppm, and
other two CH protons at d 7.376–7.402 ppm which matches well
Table 3
Calculated and experimental 1H NMR chemical shifts (d/ppm) of PT and EDTEPC in DMSO-d6 solvent at 25 °C.
PT
EDTEPC
Atom
Atom
dcalcd.
dexp.
Assignment
dcalcd.
dexp.
Assignment
H2
6.6555
7.8449
7.8504
7.4829
7.5326
2.1853
2.5696
2.2102
8.7069
6.2371
6.3312
7.1297
6.9571
9.236
6.674–6.620
7.190–7.136
(s, 1H, hydrazone-NH)
(t, 4 H, phenyl group)
H27
H28
H29
H30
H31
H32
H33
H34
H35
H36
H37
H38
H39
H40
H43
H41
H42
H44
H45
H46
H47
H48
H49
9.034
11.396
2.065
(s, 1H, pyrrole-NH)
(s, 1H, methyl-Me3)
H10
H12
H14
H15
H17
H18
H19
H27
H28
H29
H30
H31
2.0641
2.7524
2.2788
2.1946
2.8439
1.8208
4.2718
4.2459
1.1776
1.4213
1.4483
7.2276
8.1038
7.9637
7.774
7.6809
2.2247
2.2693
2.5644
2.1908
1.9569
1.6908
2.101
(s, 1H, methyl-Me2)
2.366
(s, 3H, ACH3)
4.158–4.228
1.234–1.281
(q, J = 7.00 Hz, 2H, ester-CH2)
11.503
6.928–6.902
(s, 1H, pyrrolic NH)
(d, 3H, pyrrolic CH)
(t, J = 7.05 Hz, 3H, ester methyl-Me1)
7.259
6.928–6.902
(s, 1H, ACH@N, azomethine proton)
(d, 3H, pyrrolic CH)
10.172
7.735–7.762
(s, 1H, NNH)
(d, 2H, ArACH)
7.376–7.402
2.37
(d, 2H, ArACH)
(s, 1H, methyl-Me5)
2.003
(s, 1H, methyl-Me4)
Table 4
Comparison between experimental and calculated electronic excitations: E/eV, oscillatory strength (f), absorption wavelength (k/nm) at TD-DFT/B3LYP/6-31G(d,p) level of PT and
EDTEPC.
S. no.
Excitation
E
(f)
(k)calcd.
(k)exp.
Assignment
PT
1
2
69 ? 72 (H ? L + 2)
69 ? 71 (H ? L + 1)
69 ? 70 (H ? L)
4.6209
4.3719
3.9102
0.1314
0.3146
0.2992
268.31
283.59
317.08
234
342
p
p
?
?
p⁄
p⁄
3
EDTEPC
1
2
100 ? 102 (H ? L + 1)
99 ? 103 (H-1 ? L + 3)
4.4290
5.1650
0.4971
0.6483
279.93
240.05
265
p
?
p⁄

548
R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
in dimer. Therefore, the observed wavenumber at 3292 cmꢂ1 is
in good agreement with the calculated wavenumber of dimer
and indicates the involvement of hydrazide NAH group in hydro-
gen bonding in the solid phase as observed in our earlier study
[26]. The observed hydrazide NAH deformation at 1323 cmꢂ1
agrees well with the calculated wavenumber at 1325 cmꢂ1. In
the experimental FT-IR spectrum of EDTEPC the NAH stretching
vibration of pyrrole (m
NAH) is observed at 3258 cmꢂ1, correlates
well with calculated wavenumber at 3105 cmꢂ1. The observed
wavenumber at 3258 cmꢂ1 is in good agreement with the hydro-
gen bonded dimer of pyrrole-2-carboxylic acid recorded in solid
state using KBr pellet at 3358 cmꢂ1 [34–37]. Therefore, solid state
spectrum of EDTEPC attribute to the vibration of hydrogen bonded
NAH group. In dimer, the stretching wavenumber of hydrogen
bond donor (NAH) is red-shifted due to the elongation of hydrogen
bond donor (NAH bond) than the hydrogen bond free NAH group
in monomer. The observed NAH wagging mode of pyrrole in
EDTEPC compounds at 615 cmꢂ1 also indicate the involvement of
pyrrole NAH group in intermolecular attraction and correlates
with earlier reported wagging mode at 602 cmꢂ1 for pyrrole NH
in dimer of syn-pyrrole-2-carboxylic acid [34].
Fig. 4. Comparison between experimental and theoretical UV–Visible spectra for PT
and EDTEPC.
CAH vibrations
by scaling down the calculated wavenumber using scaling factor
0.9608 [33], to discard the anharmonicity present in the real
system.
The pyrrole and benzene rings, in-plane (‘‘ip’’) and out-of-plane
(‘‘oop’’) CAH bending vibrations are reported in literature in the
region 3000–3100, 1300–1000 and 900–675 cmꢂ1, respectively
[37]. In the experimental FT-IR spectra of PT and EDTEPC, the
NAH vibrations
observed Ar-m
CH of ring at 3100, 3027 cmꢂ1 corresponds to the cal-
In the experimental FT-IR spectrum of PT, the NAH stretch of
culated wavenumber at 3104, 3062 cmꢂ1, respectively. The calcu-
lated band at 833, 793 cmꢂ1 is attributed to the CAH wagging
(an out-of-plane deformation) of benzene ring. In theoretical and
observed FT-IR spectra, weak mCAH pyrrole ring are assigned in
pyrrole (m
NAH) is observed at 3490 cmꢂ1, whereas it is calculated
at 3528 cmꢂ1. The stretching vibration of hydrazide NAH is
observed at 3292 cmꢂ1, whereas this is calculated at 3188 cmꢂ1
Fig. 5. Molecular orbital plots involved in high oscillator strength electronic excitations for PT and EDTEPC.

R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
549
Table 5a
Theoretical (selected) and experimental vibrational wavenumbers of PT and their assignments: wavenumbers (V/cmꢂ1), Intensity (km molꢂ1).
Mode no.
Intensity
Assignment (PED) P 5%
V Unsc. V Scal.
V Exp
180
178
176
175
174
173
172
171
170
169
168
167
166
165
164
163
162
161
160
159
158
157
156
155
154
3672
3318
3280
3280
3264
3264
3253
3253
3231
3231
3224
3224
3186
3186
3185
3184
3132
3132
3105
3105
3104
3104
3042
3042
1685
3528
3188
3152
3152
3136
3136
3125
3125
3104
3104
3098
3098
3061
3061
3060
3059
3009
3009
2984
2984
2982
2982
2923
2923
1619
97.63
1353.11
2.9
3490
3292
m
m
m
m
m
m
m
m
m
m
m
4
m
m
(N20H27)(86)
m(N51H58)(13)
(N1H2)(39)- (N32H33)(38)-(s-H2C56)(5)(s-C25H33)(5)
m
(C52H62)(62)
(C21H31)(62)
m
m
(C53H59)(32)
(C22H28)(32)
4.08
3.29
4.85
3.63
5.55
1.11
2.82
2.98
(C54H60)(39)-
(C23H29)(40)-
(C54H60)(54)-
(C23H29)(54)-
(C38H41)(29)-
m
(C52H62)(30)
(C21H31)(30)
(C53H59)(37)
(C22H28)(38)
m
m
m
m
(C53H59)(28)
m
m
m
m
(C22H28)(28)
(C52H62)(6)
(C21H31)(6)
(C39C42)(25)(das-R4)(21)
(C39C42)(5)
(S3C6)(25)-(das-R4)(19)-(das-R4)(10)
(S3C6)(32)-(das-R4)(24)- (C8H12)(22)-(das-R4)(13)(
m(C37C38)(12)
3100
(C7H10)(79)
(C8H12)(37)4
m
m(C38H41)(6)-m
m
0.26
m
s
-C40C43)(5)
11.24
14.22
16.7
(C9H14)(85)
(C40C45)(25)-
m
(C11H15)(5)
(C40C44)(19)-(das-R4)(15)-
(C42H46)(9)-
d(C37C39H43)(57)+d(C11H15)(14)-(das-R4)(10)-
m
m
(C38H41)(14)-d(C37C39H43)(13)-(das-R4)(9)
(C11H15)(6) (C42C44)(5)
(C42H46)(9)
d(C37C39H43)(61)-(das-R4)(11)-
m
m
m
9.54
m
10.81
13.43
10.66
17.31
17.54
16.7
25.31
19.18
115.07
m
m
m
m
m
m
m
m
(C16H17)(57)-
(C47H48)(58)-
(C56H61)(95)
(C25H30)(95)
(C16H19)(40)-
m
m
(C16H18)(41)
(C47H49)(38)
2994
2975
m
(C16H18)(37)-
m
(C16H17)(22)
2982
2925
2926
1677
(C47C50)(41)-
m
(C47H49)(39)-
(C47H49)(21)
(C16H18)(20)
m(C47H48)(20)
(C47H48)(19)
(C47C50)(58)
m
m
(C16H19)(58)
m
m(C16H17)(19)
(q
-C56N57H61)(33)-
m
(C56N57)(13)(
s-O4C56)(9)-(
q
-C25N26H30)(7)-(
s
-C40C43)(6)
m
(C25N26)(6)-
-C25H33)(5)-(s-H2C56)(5)
d(C37C39H43)(6)
153
152
151
150
149
148
147
146
145
144
143
142
141
140
139
138
137
136
135
134
133
132
131
130
129
128
127
126
125
124
123
122
121
120
119
118
117
116
115
114
113
112
111
110
109
108
107
106
1685
1654
1654
1627
1627
1607
1606
1536
1535
1531
1514
1505
1505
1502
1501
1492
1486
1469
1469
1466
1463
1441
1441
1427
1427
1379
1373
1352
1352
1335
1335
1323
1323
1316
1316
1277
1277
1235
1235
1213
1210
1147
1147
1144
1142
1135
1130
1120
1619
1590
1589
1563
1563
1544
1543
1475
1475
1471
1454
1446
1446
1443
1442
1434
1428
1412
1412
1409
1405
1385
1384
1371
1371
1325
1319
1299
1299
1283
1282
1271
1271
1264
1264
1227
1227
1187
1187
1165
1162
1102
1102
1099
1097
1091
1086
1076
25.49
25.39
12.98
1.18
3.8
1618
(q
-C56N57H61)(30)-
-C40C43)(54)d(C37C39H43)(38)
(C@N)(54)d(C37C39H43)(38)
-C40C43)(51)d(C37C39H43)(41)
m
(C56N57)(12)(
q-C25N26H30)(11)-
m
(C25N26)(9)(
s
-O4C56)(8)-(
s
(s
1588
1564
1578
m
(s
(s-C40C43)(51)d(C37C39H43)(41)
0.33
d(N1H2S3)(36)-(
d(N1H2S3)(36)-d(N32HH33S34)(12)-(
d(C37C39H43)(57)(
d(C37C39H43)(57)(
s-H2C56)(14)-(
s
-C25H33)(14)d(N32HH33S34)(12)
5.67
9.93
4.06
19.8
194.38
7.2
1514
s
-H2C56)(11)( -C25H33)(10)
s
s
s
-C40C43)(42)
-C40C43)(42)
d(N1H2S3)(32)-d(C37C39H43)(19)-(
d(N1H2S3)(41)-( -H2C56)(16)( -C25H33)(16)-d(N32HH33S34)(13) d(N1N26)(5)
d(C37C39H43)(52)- (C37C38)(22)- (C38H41)(9)(das-R4)(5)
(das-Me)(46)(das-Me)(14)-d(N1H2S3)(12)-( -Me)(6)
(das-Me)(68)-(das-Me)(17)-( -Me)(7)
d(C37C39H43)(19)- (C38H41)(18)(das-Me)(14)-(R4-Puckering)(14)(
d(N1H2S3)(45)d(N32HH33S34)(15)-( -H2C56)(13)-( -C25H33)(13) d(N1N26)(7)
d(N1H2S3)(42)-( -H2C56)(15)( -C25H33)(15)-d(N32HH33S34)(14) d(N1N26)(5)
d(N1H2S3)(32)d(N32HH33S34)(11)-( -C25H33)(8)-( -H2C56)(8)- (N51C55)(5)
-C25H33)(10)-d(N32HH33S34)(8)- (N20C24)(5)
-C25H33)(15)d(N32HH33S34)(14) d(N1N26)(5)
-C25H33)(14)-d(N32HH33S34)(13)d(C37C39H43)(5) d(N1N26)(5)
-C40C43)(42)
-C40C43)(42)
s-C40C43)(14)d(N32HH33S34)(10)-(s-H2C56)(9)-(s-C25H33)(9)
s
s
1451
1444
m
m
7.2
q
6.24
6.97
1.33
21.3
8.53
48.77
2.92
5.8
q
m
s-R4)(12)-m(C37C38)(9)
s
s
s
s
s
s
m
m
d(N1H2S3)(25)-(
d(N1H2S3)(43)-(
d(N1H2S3)(41)-(
s-H2C56)(11)(
s-H2C56)(15)-(
s-H2C56)(14)(
s
s
s
3.22
13.94
0.21
1382
1379
d(C37C39H43)(56)(
d(C37C39H43)(56)(
s
s
(
s
-C40C43)(44)d(C37C39H43)(26)-(ds-Me)(17)
(ds-Me)(55)( -C40C43)(19)d(C37C39H43)(8)-(ds-Me)(6)
-C40C43)(23)d(C37C39H43)(21) d(N1H2S3)(17)-( -H2C56)(11)-(
d(N1H2S3)(31)-( -C40C43)(16)-d(C37C39H43)(16)-d(N32HH33S34)(10)-(
0.75
s
m
(C13C16)(5)
-C25H33)(11)d(N32HH33S34)(6)
-H2C56)(6)( -C25H33)(6)
6.98
43.25
0.17
3.26
0.14
2.99
66.2
8.85
337.45
55.36
4.17
14.44
0.85
2.37
2.98
0.89
18.07
4.94
3.87
12.99
392.34
125.55
18.65
1323
1319
(s
s
s
s
s
s
(
(
s
s
-40C43)(47)d(C37C39H43)(39)
-40C43)(47)d(C37C39H43)(38)
m
m
(C40C44)(5)
(C40C44)(5)
d(C37C39H43)(51)(
(S@O)(51)(
-C40C43)(50)d(C37C39H43)(45)
-C56N57H61)(39)( -C25N26H30)(10)(
s-C40C43)(49)
1279
1274
m
s-C40C43)(49)
(
(
(
(
s
q
s
s
q
s-O4C56)(8)d(C37C39H43)(5)(
s
-C40C43)(5)
-C40C43)(49)d(C37C39H43)(40)
-C40C43)(50)d(C37C39H43)(45)
as(S@O)(55)+d(N1H2S3)(31)
1233
m
(q-C56N57H61)(30)d(N32HH33S34)(14)-(s-C25H33)(13)(s-O4C56)(6)-d(C53C54H60)(5)-d(N1H2S3)(5)
d(C37C39H43)(48)(
(s-C40C43)(47)d(C37C39H43)(46)
d(C37C39H43)(54)(
1189
1188
s-C40C43)(46)
s-C40C43)(45)
d(C37C39H43)(54)(
s-C40C43)(45)
(s
-C40C43)(56)d(C37C39H43)(43)
(S@O)(55)d(C37C39H43)(44)
1108
m
(s
-C40C43)(55)d(C37C39H43)(44)
-C40C43)(55)d(C37C39H43)(45)
-C40C43)(64)d(C37C39H43)(27)
-C40C43)(63)d(C37C39H43)(31)
-C40C43)(60)d(C37C39H43)(33)
(
(
(
(
s
s
s
s
(continued on next page)

550
R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
Table 5a (continued)
Mode no.
Intensity
Assignment (PED) P 5%
V Unsc. V Scal.
V Exp
105
104
103
102
101
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
77
76
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
1120
1103
1102
1085
1071
1065
1065
1063
1063
1033
1033
1014
1014
999.3
999.1
985.6
977.9
973
1076
1059
1059
1042
1029
1024
1024
1022
1021
992
992
974
974
960
960
947
940
935
932
932
932
881
878
862
862
819
797
796
784
783
777
777
758
752
705
705
696
686
683
657
656
634
623
623
619
607
606
605
563
554
528
528
527
527
502
499
459
459
419
166.5
78.77
4.43
323.13
4.71
14.18
14.52
127.65
16.94
0.44
23.33
0.55
0.62
0.61
2.45
0.21
1.73
0.28
2.96
22.3
2.8
88.83
309.77
0.18
(
(
(
(
(
s
s
s
s
s
-C40C43)(59)d(C37C39H43)(37)
-C40C43)(51)d(C37C39H43)(32)
-C40C43)(57)d(C37C39H43)(33)
-C40C43)(63)d(C37C39H43)(35)
-C40C43)(62)d(C37C39H43)(36)
(R4-Puckering)(44)-(
s-R4)(29)(
s-C40C43)(16)d(C37C39H43)(5)(
x-C39H43)(5)
(s
(s
(s
(s
(s
(s
(s
(s
-C40C43)(39)d(C37C39H43)(27)-(q
-Me)(16)
-C40C43)(59)d(C37C39H43)(26)
-C40C43)(60)d(C37C39H43)(34)
-C40C43)(60)d(C37C39H43)(35)
-C40C43)(68)d(C37C39H43)(28)
-C40C43)(61)d(C37C39H43)(18)(
-C40C43)(60)d(C37C39H43)(32)
1021
998
992
x
-C39H43)(11)
-H2C56)(33)-(
s
s
-C25H33)(33)-d(N1H2S3)(8)
-H2C56)(12)-( -C25H33)(11)-d(N1N26)(11)d(N32HH33S34)(5)-(x-C39H43)(5)+x(C25H30)(5)
d(N1H2S3)(17)-(
s
943
(x
(x
(x
(x
-C39H43)(63)(
s
-C40C43)(36)
-C40C43)(32)
-C40C43)(42)
-C40C43)(37)
-C39H43)(64)(
-C39H43)(49)(
-C39H43)(58)(
s
s
s
970.5
970.2
970
x
(C25H30)(33)(
-C39H43)(27)+
-H2C56)(30)( -C25H33)(29)+d(N1N26)(15)-d(N1H2S3)(7)d(N57N32)(5)
-H2C56)(26)-( -C25H33)(25) d(N1N26)(15)-d(N1H2S3)(9)-d(N57N32)(5)
-H2C56)(22)( -C25H33)(20)d(N1N26)(17) d(R1)(7)d(R3)(6)
-C25H33)(22)-( -H2C56)(21)-d(N1N26)(13)+d(R3)(7)-d(R1)(6)
s
-H2C56)(22)
x
(C56H61)(20)(
s
-C25H33)(19)
s
(
(
(
(
(
(
(
(
(
(
x
x
(C25H30)(21)(
s
-C40C43)(19)(
-C25H33)(11)-(s-H2C56)(10)-x(C56H61)(9)
917
896
833
s
s
s
s
x
x
x
s
s
s
914.2
896.9
896.9
852.7
829.9
828.1
815.9
815.2
809.1
809
788.4
782.9
734.2
733.9
724.8
714.1
710.9
683.9
683.1
659.9
648.9
648.1
644
631.9
631.1
629.8
586.1
576.3
550
549.6
548.7
548.1
522.7
519.5
477.8
477.5
436.2
7.1
3.36
1.65
23.66
10.03
11.45
44.41
2.63
s
-C39H43)(53)(
-C39H43)(68)(
-C39H43)(70)(
s-C40C43)(47)
s-C40C43)(27)
s-C40C43)(26)
792
778
s
-C40C43)(75)d(C37C39H43)(10)-(das-R4)(7)(
x
-C39H43)(6)
-C39H43)(16)d(C37C39H43)(6)-(das-R4)(4)
-C25H33)(23)-( -C40C43)(16)( -H2C56)(11)
-H2C56)(16)( -C39H43)(15)( -C25H33)(10)
-C25H33)(22)d(N57N32)(10)
-H2C56)(23)d(N57N32)(9)
-C25H33)(23)d(N57N32)(10)
(C25H30)(12)-(R4-Puckering)(12) d(N1N26)(9)(
(R4-Puckering)(29)-d(N1N26)(24)-( -H2C56)(14)-( -C25H33)(13)-d(N57N32)(8)-(
s
-C40C43)(72)(
x
x
(C25H30)(25)(
s
s
s
x
(C56H61)(7)-(
x
-C39H43)(5)
(C56H61)(7)
773
749
757
(s
-C40C43)(35)-(
s
x
s
x(C25H30)(7)-
x
4.53
d(N1N26)(31)(
s
-H2C56)(25)(
s
s
35.89
170.38
6.69
206.93
14.05
50.36
8.9
2.09
132.63
0.02
(s
-C25H33)(25)-d(N1N26)(24)-(
s
d(N1N26)(29)(
(C52H62)(13)-
s-H2C56)(24)(
x
x
(C21H31)(13)
x
s-C40C43)(7)-
x(C56H61)(6)
694
656
624
s
s
s-C40C43)(5)
(R4-Puckering)(64)(
(R4-Puckering)(50)(
x
x
-C39H43)(30)
-C39H43)(40)
(
(
s
s
-C25N26)(41)-(
s
-C56N57)(19) d(N1N26)(14)-
-C56N57)(20)-( -C39H43)(12)-
-C25H33)(19)-d(N57N32)(10)-(
x
(C25H30)(10)-d(N57N32)(5)
(C25H30)(9)-(R4-Puckering)(6)-
-C40C43)(7)-( -C39H43)(5)
x
(C56H61)(5)
-C25N26)(36)(
s
x
x
x
(C56H61)(5)
d(N1N26)(29)(
s
-H2C56)(19)-(
s
s
x
(
(
s
s
-C40C43)(69)(das-R4)(22)d(C37C39H43)(6)
-C40C43)(64)(das-R4)(26)d(C37C39H43)(7)
1.34
38.15
22.61
1.93
46.46
188.21
18.58
143.19
16.78
38.8
49.99
4.54
41.3
9.02
1.82
(das-R4)(27)(
d(N1N26)(30)(
-C25N26)(30)(
s
-H2C56)(20)(
-H2C56)(23)-(
-C56N57)(18)(
s
-C25H33)(19) d(N1N26)(15)d(N57N32)(5)
-C25H33)(23)-d(N57N32)(10)
-C25H33)(10)-( -R3)(10)-(
-C25H33)(26)-d(N57N32)(9)
-C39H43)(15)( -H2C56)(14)-(
-R4)(16)-d(N1N26)(10)
-C25N26)(11)d(C37C39H43)(9)-
-C56N57)(10)-( -C25N26)(9)- (C56H61)(7)(
-R4)(24)-d(C37C39H43)(12)( -C39H43)(8)-( -C40C43)(8)
-C40C43)(22)-( -R4)(12)-d(C37C39H43)(10)-d(N1N26)(8)
s
s
(s
s
s
s
s-R1)(9)
d(N1N26)(27)(
d(N1N26)(19)(
s
-H2C56)(26)-(
s
558
482
s
-C40C43)(17)(
x
s
s-C25H33)(14)-(s-R4)(9)-d(N57N32)(6)
(s
(s
(s
-C40C43)(35)(
-C40C43)(33)-(das-R4)(25)(
-C40C43)(29)-( -R4)(18)(
x-C39H43)(21)-(s
s
x
(C25H30)(7)
-C39H43)(6) x(C25H30)(6)
s
s
s
x
x
s
x
(das-R4)(37)-(
(das-R4)(36)-(
s
s
s
(s
(s
(s
(s
(s
-C40C43)(68)-(
s-R4)(24)
-C40C43)(67)-(
s-R4)(23)(x-C39H43)(5)
-R4)(51)-(
-R4)(52)-(
-R4)(35)-(
s
s
s
-C40C43)(44)
-C40C43)(43)
-R4)(10)(das-R4)(10)-(
456
427
1.44
q
-SO2)(8)d(C37C39H43)(6)(R4-Puckering)(5)
Proposed assignment and potential energy distribution (PED) for vibrational modes: types of vibrations:
m
– stretching, dsc – scissoring,
q
– rocking,
x – wagging, t – twisting,
d – deformation, ds – symmetric deformation, das – asymmetric deformation, dip – in plane deformation, doop – out of plane deformation,
s
– torsion, R1 and R3 – pyrrole ring,
R2 and R4 – phenyl ring, Me – methyl on phenyl ring.
the range of 3128–3143 cmꢂ1 in both PT and EDTEPC. The CH3
group associate with six types of vibrational frequencies namely:
attached to the pyrrole ring, remaining is attached to the CH2 of
ester group, azomethine carbon and benzene ring. The CAH
stretching vibrations of methyl groups and CH2 of ester group are
observed at 2925 cmꢂ1 and is also corresponds with the earlier
reported absorption band at 2990–2850 cmꢂ1 in the region [39].
The observed wavenumbers in the region 1423 cmꢂ1 designates
in-plane deformation mode of methyl groups. The observed wave-
numbers at 774 cmꢂ1 assign to the out-of-plane deformation mode
symmetric stretch (
m
s), asymmetric stretch (
mas), scissoring (dsc),
rocking ( ), wagging (
q
x
) and twisting (t), according to internal
coordinate system recommended by Pulay et al. [38]. As we know
that scissoring and rocking deformations belong to polarized in-
plane vibration, whereas wagging and twisting deformations
belong to depolarized out-of-plane vibration. In EDTEPC five
methyl groups are present. Out of five two of them are directly
of methyl groups. The observed wavenumber at 774 cmꢂ1
,

R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
551
Table 5b
Theoretical (selected) and experimental vibrational wavenumbers of EDTEPC and their assignments: wavenumbers (V/cmꢂ1), intensity (km molꢂ1).
Mode
no.
Intensity
Assignment (PED) P 5%
V
V Scal,
V
Exp.
Unsc.
141
140
139
138
137
136
135
134
133
132
131
130
129
128
127
126
125
124
123
122
121
120
119
118
117
116
115
114
113
112
3649
3437
3231
3224
3187
3186
3184
3161
3161
3138
3132
3130
3105
3104
3102
3096
3082
3066
3056
3042
3042
3037
3023
1759
1665
1655
1629
1606
1550
1536
3505
3303
3105
3097
3062
3061
3059
3037
3037
3015
3009
3008
2984
2982
2980
2974
2961
2946
2936
2923
2923
2918
2904
1690
1600
1590
1565
1543
1489
1476
108.62
10.93
1.11
3386
3258
3027
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
(N1H27)(9) + C24H43(20)
(N15H39)(90)-(
(C24H43)(97)
(C20H40)(96)
q-N15N14S16)(8)
1.46
10.38
14.59
7.95
6.68
1.93
35.49
12.43
28.44
7.83
(C23H42)(91)m(C21H41)(5)
(C21H41)(90)-
m
(C23H42)(6)
(C26H47)(93)-
m
(C26H49)(5)
(C9H32)(84)-
(C7H29)(87)-
m
m
(C9H33)(13)
(C7H28)(10)
(C13H38)(46)-
(C25H44)(51)-
(C13H36)(64)-
(C12H34)(43)-
(C25H46)(40)-
m
m
m
m
m
(C13H37)(38)-
(C25H45)(48)
(C13H37)(20)-
(C12H35)(41)
(C25H45)(31)-
m
(C12H35)(8)
m
(C12H34)(7)
2992
m
(C13H38)(14)
m
(C13H37)(8)-
m(C13H38)(8)
18
m(C25H44)(29)
m(C9H32)(8)
18.35
24.12
9.59
2925
2816
(C9H33)(70)-
m
(C9H31)(21)
(C7H28)(51)-
m
(C7H30)(47)
(C26H49)(73)-m(C26H48)(24)
23.17
16.84
22.17
24.74
29.19
11.94
409.12
12.64
21.59
1.18
(C12H35)(50)
(C13H36)(35)
(C25H46)(57)
m
m
m
(C12H34)(48)
(C13H37)(33)
(C25H45)(18)
m
m
(C13H38)(32)
(C25H44)(18)
(C7H29)(8)
(C9H32)(6)
2707
(C7H30)(48)
m
(C7H28)(37)
m
m
(C9H31)(78)
m
(C9H33)(16)
(C26H48)(75)m(C26H49)(20)
1665
1598
(C6O10)(85)
(C8N14)(67)(d-C8N14N15)(8)
(C20C21)(21) (C23C24)(21)(das-R1)(10)-
(C19C24)(20)-(das-Me1)(19) (C21C22)(17)-
(C2C3)(28)- (C4C5)(18)-d(C2H27N1)(10)-
(C2C3)(18) (N1C5)(17)- (C5C7)(12)
d(C19H40C20)(15)( -C24H43)(14)-d(C22H42C23)(11)d(C20H41C21)(11)-(das-
Me1)(9) (C19C24)(9) (C21C22)(7) (C22C23)(6)
(N1C5)(13)-(das-Me2)(10) (C4C8)(9)- (C3C4)(8)-
(dsc-CH2)(59) (N1H27)(15)(das-Me1)(5)- (C2C3)(4)
(das-Me4)(43)-(das-Me2)(15)(das-Me3)(15)-(das-Me3)(7)
(N1H27)(37)-(dsc-CH2)(18)-(das-Me3)(13)(das-Me1)(10)-(das-Me3)(7)(das-Me4)(6)
(das-Me3)(36)(das-Me3)(15)-(dsc-CH2)(11) (N1H27)(11)-(das-Me4)(6)(das-Me1)(6)
(das-Me5)(81)-( -Me5)(6)
(das-Me4)(41)-das-Me3)(12)(das-Me3)(9)-(das-Me2)(5)
(das-Me5)(89)-( -Me5)(6)
(das-Me1)(63)- (N1H27)(21)-(
(das-Me3)(33)(das-Me4)(22)(das-Me2)(16)(das-Me2)(5)-(das-Me4)(5)
(das-Me2)(50)(das-Me4)(12)-(das-Me3)(5)- (N1C2)(5)
(das-Me2)(29)(das-Me4)(16)-(das-Me2)(15) (C4C8)(8)-(das-Me3)(5)-
(C2C6)(13)(das-Me2)(10)d(R1)(25)
(C23C24)(21)- (C20C21)(20)d(C20H41C21)(11)d(C22H42C23)(11)(das-Me5)(9)(
m
m
(C22C23)(8)-
m
(C21C22)(7)d(C22H42C23)(7)
m
m
(C22C23)(17)(das-R1)(9)
88.16
68.27
4.52
1566
1515
m
m
(C2C6)(7)
m
(C4C8)(5)-
m(C8N14)(5)
m
m
m(C4C5)(7)d(C2H27N1)(7)-m(N1C2)(6)d(R)(5)
x
m
m
m
111
110
109
108
107
106
105
104
103
102
101
100
99
1536
1533
1517
1513
1510
1504
1503
1503
1501
1493
1489
1480
1469
1442
1476
1472
1457
1454
1450
1445
1444
1444
1442
1434
1431
1422
1411
1385
12.77
8.99
9.09
0.72
8.29
13.36
10.36
5.71
4.99
20.46
6.34
1492
m
m
m
m(C4C5)(6)-(das-Me3)(6)
m
m
5m
m
q
q
m
q-Me1)(7)
1423
1420
m
m
55.19
224.46
9.36
m(C3C4)(5)
m
m
(N1C2)(14)-m
98
m
x
-C24H43)(8)-
d(C19H40C20)(8)d(C21C25C22)(5)
(dS-Me1)(45)-(dS-Me2)(16)-( -CH2)(14)
(dS-Me3)(76) (C3C9)(7)(dS-Me2)(6)
(dS-Me2)(56)(dS-Me1)(21)-(dS-Me3)(5)
(dS-Me5)(88) (C22C25)(8)
(C4C8)(63)-( -N15N14S16)(15)
-CH2)(23)-( -N15N14S16)(14)(dS-Me1)(11)
-N15N14S16)(38)( -CH2)(20) (C4C8)(11)(dS-Me1)(6)-
-N15N14S16)(25) (C3C4)(14) (N1C5)(10)- (C4C5)(6)-(
(C21C22)(18) (C19C24)(15)-(das-Me1)(15)
d(C19H40C20)(21)-( -C24H43)(20)d(C22H42C23)(19)d(C20H41C21)(18)(das-Me1)(5)-
(S16O17)(36)- (S16O18)(31)-( -N15N14S16)(5)
(t-CH2)(18)- (N1C2)(10)- (C4C8)(9)(C3C4)(7) (C8C26)(7)
(t-CH2)(61)( -Me1)(8) (N1C2)(4) (C4C8)(3) (C3C4)(3)- (C8C26)(2)
(C6O11)(25)d(C2H27N1)(13)- (C2C6)(12)-d(O10O11C6)(9)-( -CH2)(8)-
(C21C22)(7)d(C20H41C21)(7)-
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
1437
1432
1427
1427
1417
1401
1394
1380
1354
1335
1322
1298
1298
1284
1235
1381
1376
1371
1371
1361
1346
1340
1326
1301
1283
1270
1248
1247
1234
1187
13.72
1.5
47.25
1.09
29.68
14.81
1.44
22.71
2.19
x
m(C12C13)(10)
m
m
8
m
q
(
(
(
x
q
q
q
m
(C3C4)(9)-
m
m
x
(C4C5)(8)-d(R)(5)
(N1C5)(3)
-CH2)(6)-d(R)(5)-
(C20C21)(10)- (C23C24)(9)
(C19C24)(5)
x
m
m
m
1305
1285
m
m(C4C8)(5)
m
(C22C23)(18)-
m
m
m
m
3.57
x
m
104.61
48.97
15.73
762.06
1.74
m
m
q
m
q
m
m
m(C3C9)(5)d(N14C4C8)(5)
m
m
m
m
1233
1187
m
m
m
m
x
m(N1C2)(6)
(C22C25)(43)-(dtrigonal-R1)(13)-d(C22H42C23)(7)-
m
m
(C22C23)(6)-
m
(C20C21)(5)-
(C23C24)(5)
82
81
80
79
78
77
76
75
74
73
72
1213
1211
1185
1143
1142
1142
1134
1106
1090
1086
1065
1165
1163
1138
1098
1098
1097
1089
1063
1047
1043
1024
4.67
4.99
3.96
61.95
137.9
12.4
179.13
7.89
d(C2H27N1)(34)
m(N1C2)(20)(q-Me3)(5)
1156
1092
d(C20H41C21)(20)-d(C19H40C20)(18)-(
x
-C24H43)(17)-d(C22H42C23)(17)
-Me1)(36)-(t-CH2)(6)(das-Me1)(4)-5 (N1H27)(1)
(C12C13)(10)- (S16O18)(10)- (S16O17)(8)- (C6O11)(8)(dsc-C12O11C13)(8)
(S16O18)(13)- (S16C19)(12)( -Me1)(10) (C19C24)(6)- (C12C13)(5)d(C19H40C20)(5)(das-Me1)(5)
-C24H43)(18) (C20C21)(15)d(C20H41C21)(14)d(C22H42C23)(14)- (C23C24)(13)-d(C19H40C20)(12)
(O11C12)(17)-( -Me1)(12)- (C6O11)(10)d(R)(9) (C3C9)(8)-d(N14C4C8)(5)
(N14N15)(35)( -Me3)(12)-d(N14C4C8)(7)-( -Me4)(5)
-Me4)(28)-d(R)(12) (C5C7)(7)d(N14C26C8)(7)( -Me3)(7)
(S16O18)(20) (S16O17)(17)-(das-Me1)(11)- (C19C24)(11)
-Me5)(48)( -Me5)(15)(doop-C22C25)(10)-(R1-puckering)(7)(das-Me5)(5)-(
m
(C20C21)(10)
m
(C23C24)(9)
(
q
-CH2)(51)(
q
m
m
(q
-Me1)(17)-
(S16O17)(14)
m
m
q
m
m
(S16C19)(6)
m
m
m
m
m
(x
m
m
1018
m
m
q
m
m
m
(N14N15)(5)
q
q
34.39
150.1
13.02
(q
m
q
m
(C4C5)(6)d(R)(5)
m
m
m
m(N14N15)(5)
(q
q
x
-C24H43)(5)-(
x
-C21H41)(5)
(continued on next page)

552
R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
Table 5b (continued)
Mode
no.
Intensity
Assignment (PED) P 5%
V
V Scal,
V
Exp.
Unsc.
71
70
69
68
66
64
63
62
61
60
59
1064
1059
1053
1049
1033
1007
982
979
972
906
897
1022
1017
1012
1008
992.4
967.6
943.9
940.6
933.9
870
6.77
6.47
1.62
48.87
6.35
2.81
18.54
0.46
0.74
(
(
(
q
q
q
-Me3)(68)(doop-C3C9)(7)(
-Me2)(42)( -Me2)(10)( -Me4)(9)-doop-C5C6)(6)(das-Me2)(5)
-Me4)(21)-( -Me2)(17)( -Me3)(11)-d(C8C26)(7)-( -Me2)(6)-
(O11C12)(31)
(dtrigonal-R1)(62)- (C22C23)(9)-
-Me2)(36)-( -Me2)(16)( -Me3)(11)-
(C8C26)(36)( -Me4)(16) (N14N15)(10)-d(N15H39N14)(8)
-C20H40)(30)-( -C21H41)(28)(
-C24H43)(31)( -C24H43)(22)-(
(O11C12)(23)( -Me1)(13)
s-R)(6)
q
q
q
q
q
m(N14N15)(6)
953
m(C12C13)(42)-m
m
m
(C21C22)(8)
(N1C5)(10)d(R)(5)(das-Me2)(5)
(C8N14)(6)
-C24H43)(16)( -R1)(8)
-C20H40)(18)(R1-puckering)(14)( -C21H41)(11)
(N15S16)(6)-d(N15H39N14)(5)
m(S16C19)(3)(das-Me1)(2)
(q
q
q
q
m
m
m
m
(x
x
x
x
-C24H43)(17)(
x
s
(x
x
q
x
31.41
836
815
m
m
m
(C12C13)(12)
m
862.1 278.97
(N15S16)(22)-d(N15H39N14)(13)-
m
(O11C12)(9)-
m
(N14N15)(8)-(
q
-N15N14S16)(8)-(
q
-Me4)(7)(d-C8N14N15)(7)-
(q-Me1)(5)
58
56
53
52
51
50
49
48
47
45
44
43
42
41
40
39
38
37
864
828
768
754
720
718
708
653
650
636
614
598
581
558
537
510
496
479
830
796
25.67
18.25
17.95
15.76
9.76
79.72
50.04
56.84
19.5
11.04
50.16
90.67
11.95
36.34
85.12
30.66
14.89
10.01
d(O10O11C6)(17)
-C21H41)(20)(
d(R)(27)d(O10O11C6)(17)
m
x
(C6O11)(16)-d(C12C6O11)(14)(
q
x
-Me1)(11)
-C20H40)(17)-(
(C3C9)(12)d(C3C8C4)(5)
-R)(8)
-C4C8)(8)(doop-C3C9)(7)(
(R1-puckering)(52)-(doop-C16C19)(7)-(doop-C22C25)(7)
m
(C2C3)(5)
793
774
741
(x
-C24H43)(20)-(
x
-C24H43)(18)(
s-R1)(8)
737.7
724
691.7
689.4
679.9
627
624.5
611.3
589.9
574.4
558.3
535.8
515.9
490.1
476.5
460
m
(C5C7)(16)-m
(doop-C2C6)(48)(doop-C2C6)(17)(
s-C6C2)(16)(s
(s-R)(34)-(doop-C4C8)(22)-(doop-C5C6)(9)-(
s
s-R)(5)
685
615
(R1-puckering)(48)-(doop-C22C25)(6)
m
(C8C26)(5)
-SO2)(6)-d(C3C8C4)(5)-
m
(S16C19)(10)-d(N1C6C2)(7)-d(C2C9C3)(7)(
x
m
(C22C25)(5)
(x
-N1H27)(53)-(doop-C3C9)(11)-(
s-R)(10)
m
(S16C19)(10)-(
-N1H27)(39)(s
x
-N15H39)(10)d(C8C26)(7)(das-R1)(6)d(C3C8C4)(6)-
-R)(36)(doop-C2C6)(7)-(doop-C5C6)(5)
-N15N14S16)(17) (N15S16)(12)
-N15N14S16)(11)d(R)(10)- (C5C7)(7)-
-N15H39)(7)-( -N15N14S16)(6)( -C4C8)(5)
-SO2)(19)d(C8C26)(11)-(das-R1)(10)( -N15H39)(8)(dsc-SO2)(6)-(
-R1)(12)(doop-C16C19)(6)-(doop-C22C25)(6)-(dsc-SO2)(6)d(N15H39N14)(5)
-SO2)(14)d(C8C26)(8)
m(C22C25)(5)d(N1C6C2)(5)
(
(
(
x
x
x
-N15H39)(35)(
-N1H27)(25)(
q
m
553
q
m
m(C3C9)(7)
d(C8C26)(26)-(
x
q
s
(
(
(
(
x
x
x
x
s-R1)(5)
-N15H39)(22)(
-N15H39)(27)(
q
q
-N15N14S16)(12)-(
-N15N14S16)(18)(
s
q
483
469
s
-R1)(23)-(dsc-SO2)(14)(doop-C22C25)(14)-(doop-C16C19)(9)-d(N1C7C5)(5)
Proposed assignment and potential energy distribution (PED) for vibrational modes: types of vibrations:
m
– stretching, dsc – scissoring,
q
– rocking,
x – wagging, t – twisting,
d – deformation, ds – symmetric deformation, das – asymmetric deformation, dip – in plane deformation, doop – out of plane deformation,
s
– torsion, R – pyrrole ring, R1
phenyl ring, Me, Me1, Me2, Me3, Me4, Me5 – methylgroup.
Fig. 6b. Comparison between experimental and theoretical IR spectrum for
EDTEPC.
the involvement of C@O group in intermolecular hydrogen bond-
ing. The red shift in the stretching wavenumber of hydrogen bond
acceptor (C@O) has been clearly observed in the experimental and
theoretical spectrum due to its hydrogen bond free C@O group in
monomer. The ester CAO stretching (mCAOAc) observed in EDTEPC
Fig. 6a. Comparison between experimental and theoretical IR spectrum for PT.
at 1092 cmꢂ1 and calculated and these bands occur in the region
1300–1000 cmꢂ1 in literature [40].
correspond to the earlier reported absorption band at 1440, 800–
700 cmꢂ1 in the region [40].
CAO Vibrations
CAC vibrations
The carbonyl stretching vibration is highly characteristic and
intense absorption. The stretching vibration of ester carbonyl
In aromatic hydrocarbons, the skeletal vibrations involving car-
bon–carbon stretching within the ring absorb in the 1600–
1585 cmꢂ1 and 1500–1400 cmꢂ1 region and out-of-plane bending
vibrations in substituted benzenes absorb near 694–558 cmꢂ1
[40]. The C@C stretches in EDTEPC of pyrrole is assigned at
1492 cmꢂ1, in FT-IR spectrum and also along with the reported band
in literature in the region 1420–1360 cmꢂ1 [39]. The observed
group (m
C@O) in EDTEPC observed at 1665 cmꢂ1 corroborates well
with calculated wavenumber at 1690 cmꢂ1. The observed mC@O at
1665 cmꢂ1 also corresponds to the earlier reported wavenumber
at 1665 cmꢂ1 for dimer of our previous studies of hydrazones
[35–37]. Therefore, stretching mode of mC@O in EDTEPC confirms

R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
553
Table 6
Calculated eHOMO, eLUMO, energy band gap (eL ꢂ eH), chemical potential (
(3),(5), (6) and Elecrophilicity based charge transfer (ECT) for reactant system [(1) M (2)] and [(5) M (2)] of PT and EDTEPC.
l
), electronegativity (
v
), global hardness (
g), global softness (S), global electrophilicity index (
x
) for (1), (2),
eH
eL
eH–eL
v
l
g
S
x
ECT
PT
(1)
(2)
(3)
ꢂ6.2641
ꢂ6.9128
ꢂ5.7370
ꢂ1.257
ꢂ0.8561
ꢂ1.118
5.0071
6.0568
4.619
3.7605
3.8845
3.4275
ꢂ3.7605
ꢂ3.8845
ꢂ3.4275
2.5035
3.0284
2.3095
0.1997
0.1651
0.2164
2.8243
2.4913
2.5433
0.219
EDTEPC
(5)
(2)
ꢂ6.0315
ꢂ6.9128
ꢂ5.6491
ꢂ0.8158
ꢂ0.8561
ꢂ0.9252
5.2157
6.0568
4.7239
3.4237
3.8845
3.2872
ꢂ3.4237
ꢂ3.8845
ꢂ3.2872
2.6079
3.0284
2.362
0.1917
0.1651
0.2116
2.2473
2.4913
2.2874
0.030
(6)
eH, eL, eL–eH,
v, l, g, x
(in eV) and S (in eVꢂ1).
C@N vibrations
Table 7
The observed C@N stretching vibration (mC@N) in PT and EDTEPC
Selected electrophilic reactivity descriptors (f+k, sk+, xk+
)
for reactant (1, 5) and
at 1588, 1597 cmꢂ1, matches well with the theoretically calculated
wavenumber at 1589, 1600 cmꢂ1, respectively. The observed mC@N
at 1588, 1598 cmꢂ1 also corresponds to the earlier reported wave-
number at 1602 cmꢂ1 [40]. In FT-IR spectrum of PT, the presence of
C@N band confirms the formation of hydrazone linkage in the
molecules.
nucleophilic reactivity descriptors (fꢂk , skꢂ
charges of PT and EDTEPC.
,
xꢂk ) for reactant (2), using Hirshfeld atomic
+
+
+
ꢂ
ꢂ
ꢂ
Sites
fk
sk
xk
Sites
fk
sk
xk
PT
C2
C3
C4
C6
0.0644
0.0098
0.1633
0.1402
0.0025
0.0003
0.0065
0.0056
0.5665
0.0866
1.4348
1.2323
N1
N20
0.1433
0.1566
0.0240
0.0263
0.4135
0.4516
Global and local reactivity descriptors analysis
EDTEPC
7 C
15 C
0.0143
0.0078
0.0169
0.2761
0.0321
0.0175
N1
N20
0.1433
0.1566
0.0240
0.0263
0.4135
0.4516
The chemical reactivity and site selectivity of the molecular sys-
tems have been determined on the basis of Koopman’s theorem
f+k, fꢂk (in e); s+k, skꢂ (in eVꢂ1) and x+k
,
xꢂk (in eV).
[42]. Global reactivity descriptors as electronegativity (
(eLUMO + eHOMO), chemical potential ( ) = 1/2(eLUMO + eHOMO), global
hardness ( and
) = 1/2 (eLUMO ꢂ eHOMO), global softness (S) = 1/2
electrophilicity index ) = are highly successful in
2/2
v
) = ꢂ1/2
l
g
g
(
x
l
g
predicting global reactivity trends [43–46]. The energies of frontier
Table 8
molecular orbitals (eHOMO, eLUMO), energy gap (eHOMO ꢂ eLUMO), elec-
Calculated Dipole moment (l0), Polarizability (|a0|), anisotropy of Polarizability (Da),
First Hyperpolarizability (b0) and their components, using B3LYP/6-31G(d,p) of PT
and EDTEPC.
tronegativity (v), chemical potential (l), global hardness (g), global
softness (S), global electrophilicity index (
ECT for reactant system [(1) M (2)] and [(5) M (2)] are listed in
Table 6. The global electrophilicity index ( = 2.54, 2.287 eV) of
x) for (1), (2), (3) and
Dipole moment
PT EDTEPC
Polarizability
PT
Hyperpolarizability
x
EDTEPC
PT
EDTEPC
PT and EDTEPC show these molecule behaves as
electrophile.
a
strong
lx 0.3043 1.990 axx 218.298 328.19
ly 2.2395 3.492 ayy 22.132
bxxx ꢂ929.20
959.48
245.51
99.826
ꢂ88.448
7.423 bxxy
61.37
Electrophilic charge transfer (ECT) = (
D
Nmax A
)
ꢂ (
D
Nmax B
)
is
lz ꢂ0.7493 ꢂ2.195 azz 173.263 221.57
bxyy ꢂ43.59
l0 2.1322 4.5797
|
D
a0
a
|
137.89
27.5248 byyy ꢂ31.48
defined as the difference between the Nmax values of interacting
D
94.1024 bxxz ꢂ83.05 ꢂ211.86
molecules [46]. If we consider two molecules A and B approach to
each other (i) if ECT > 0, charge flow from B to A (ii) if ECT < 0,
charge flow from A to B. ECT is calculated as 0.219, 0.030 for reac-
tant molecules [(1), (2)], [(5) and (2)], which indicates that charge
flows from (2) to (1) and (2) to (5). Therefore, (1 and 5) acts as elec-
tron acceptor (electrophile) and (2) as electron donor (nucleo-
phile). Selected local electrophilic reactivity descriptors (f+k, sk+,
x+k) [43–47], for reactant (1), (5) and nucleophilic reactivity
descriptors (fꢂk , skꢂ, xꢂk ) for reactant (2) are given in Table 7. Using
Hirshfeld charges, the maximum values of local electrophilic reac-
bxyz ꢂ91.12
byyz ꢂ31.39
ꢂ85.242
ꢂ22.051
bxzz ꢂ30.21 ꢂ129.11
byzz
bzzz ꢂ80.34
b0 6.509
28.74
1.110
7.162
8.3837
l0 in Debye; |a0| and Da
in 10ꢂ24 esu; b0 in 10ꢂ30 esu.
CACAC deformations associated with pyrrole ring at 896, 793 cmꢂ1
in PT and EDTEPC, respectively. In theoretical IR spectrum, the com-
bination bands of ‘CAC stretches and CACAH deformations’ associ-
ated with benzene ring are observed at 1451, 1420 cmꢂ1. The C@C
stretches of benzene is observed at 1566 cmꢂ1 in EDTEPC. The
observed C@C stretches of benzene at 1565 cmꢂ1 also corresponds
well with the calculated wavenumber at 1543 cmꢂ1 [40].
tivity descriptors (f+k, sk+,
x
+k) at aldehyde carbon C6, C7 of reactants
(1) and (5) indicate that these are the most electrophilic site in the
studied molecules. The nucleophilic reactivity descriptors (fꢂk , skꢂ,
xꢂk ) analysis of reactant (2) shows that N20 is the most nucleo-
philic site. Therefore, the nucleophilic attack of N20 site of reactant
(2) at the most electrophilic site C6, C7 of reactants (1) and (2) con-
firm the formation of product molecule (3) and (6) or Schiff base
linkage (C@N) in hydrazone.
S@O vibrations, SAN vibrations
The asymmetric and symmetric stretching vibrations of SO2
(mS@O) in PT and EDTEPC are observed at 1233, 1108, 1232,
1156 cmꢂ1, correlate well with the theoretical wavenumber at
1227, 1102, 1233, 1163 cmꢂ1, respectively. Thus, red shift in the
observed wavenumbers indicates the involvement of SO2 group
in hydrogen bonding in the solid state. The free asymmetric and
symmetric mS@O is also reported in the literature at 1360,
1168 cmꢂ1 for sulfonamide triazines [41].
Static dipole moment (
l0), mean polarizability (|a0|), anisotropy of
polarizability ( ) and first hyperpolarizability (b0)
D
a
In order to investigate the relationship between molecular
structure and NLO response, first hyperpolarizability (b0) of this
novel molecular system, and related properties (|a0| and Da) are

554
R.N. Singh et al. / Journal of Molecular Structure 1081 (2015) 543–554
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their nature within molecule. The red shift in both the proton
donor (pyrrole NAH) and proton acceptor (S@O) group designates
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PT molecule. In EDTEPC dimer, the stretching wavenumber of
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of hydrogen bond donor (NAH bond) than the hydrogen bond free
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standard counterpoise method. The local reactivity descriptors
analyses are performed to determine the reactive sites within mol-
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to evaluate non-linear optical (NLO) response of the investigated
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The authors are thankful to the DST New Delhi for financial
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