Molecular structure, heteronuclear resonance assisted hydrogen bond analysis, chemical reactivity and first hyperpolarizability of a novel ethyl-4-{[(2,4-dinitrophenyl)-hydrazono]-ethyl}-3,5-dimethyl-1H-pyrrole-2- carboxylate: A combined DFT and AIM appro

Article abstract of DOI:10.1016/j.saa.2012.02.086

A new ethyl-4-{[(2,4-dinitrophenyl)-hydrazono]-ethyl}-3,5-dimethyl-1H- pyrrole-2-carboxylate (EDPHEDPC) has been synthesized and characterized by FT-IR, ¹H NMR, UV-vis, DART-Mass spectroscopy and elemental analysis. Quantum chemical calculation

Full text of DOI:10.1016/j.saa.2012.02.086

Spectrochimica Acta Part A 92 (2012) 295–304
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Molecular structure, heteronuclear resonance assisted hydrogen bond analysis,
chemical reactivity and first hyperpolarizability of a novel ethyl-4-{[(2,4-
dinitrophenyl)-hydrazono]-ethyl}-3,5-dimethyl-1H-pyrrole-2-carboxylate: A
combined DFT and AIM approach
∗
R.N. Singh , Amit Kumar, R.K. Tiwari, Poonam Rawat, Vikas Baboo, Divya Verma
Department of Chemistry, University of Lucknow, University Road, Lucknow 226007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A
new
ethyl-4-{[(2,4-dinitrophenyl)-hydrazono]-ethyl}-3,5-dimethyl-1H-pyrrole-2-carboxylate
Received 2 December 2011
Received in revised form 4 February 2012
Accepted 22 February 2012
1
(EDPHEDPC) has been synthesized and characterized by FT-IR, H NMR, UV–vis, DART-Mass spec-
troscopy and elemental analysis. Quantum chemical calculations have been performed by DFT level of
theory using B3LYP functional and 6-31G(d,p) as basis set. The H NMR chemical shifts are calculated
1
using gauge including atomic orbitals (GIAO) approach in DMSO as solvent. The time dependent density
functional theory (TD-DFT) is used to find the various electronic transitions and their nature within
molecule. A combined theoretical and experimental wavenumber analysis confirms the existence of
Keywords:
DFT
Hydrogen bonded dimer
AIM
2
dimer. Topological parameters such as electron density (ꢀBCP), Laplacian of electron density (ꢀ ꢀBCP),
kinetic electron energy density (GBCP), potential electron density (VBCP) and the total electron energy
density (HBCP) at bond critical points (BCP) have been analyzed by Bader’s ‘Atoms in molecules’ AIM
theory in detail. The intermolecular hydrogen bond energy of dimer is calculated as −12.51 kcal/mol
using AIM calculations. AIM ellipticity analysis is carried out to confirm the presence of resonance
assisted intra and intermolecular hydrogen bonds in dimer. The calculated thermodynamic parameters
show that reaction is exothermic and non-spontaneous at room temperature. The local reactivity
Ellipticity
Reactivity descriptor
NLO
+
−
−
+
descriptors such as Fukui functions (fk , fk ), local softnesses (sk , sk ) and electrophilicity indices
+
−
(
(
(
ωk , ωk ) analyses are performed to determine the reactive sites within molecule. Nonlinear optical
NLO) behavior of title compound is investigated by the computed value of first hyperpolarizability
ˇ0).
©
2012 Elsevier B.V. All rights reserved.
1
. Introduction
Hydrazones are an important class of compounds due to their
antimicrobial, antitubercular [15–19] and antidiabetic agents [20].
They have also been used as potentially DNA damaging and muta-
genic agents [21,22]. They have strong coordinating ability towards
different metal ions [23,24]. In addition, aroyl hydrazones and their
mode of chelation with transition metal ions present in the living
system have been of significant interest [25,26]. The anion recep-
tor 2,4-dinitrophenylhydrazone of pyrrole-␣-carboxaldehyde has
been used for the development of potential chemosensors [27].
The chemical stability of hydrazones and their high melting points
have recently made them attractive as prospective new materials
for opto-electronic applications [28]. The nitro phenyl hydrazones
exhibit a series of good organic nonlinear optical (NLO) proper-
ties [29–31]. In particular, the interest to this compound is being
due to the above applications and fact that the pyrrole fragment
is a constituent of many biological systems. In order to obtain
information for significant application about pyrrole containing
2,4-dinitrophenylhydrazones, the title compound is synthesized
various properties and applications. They are versatile starting
materials for the synthesis of a variety of N, O or S containing
heterocyclic compounds such as oxadiazolines, thiazolidinones, tri-
azolines, and various types of other organic compounds [1–7]. Due
to the presence of ꢀN
N
Cꢁ functional frame, [2 + 2] cycloaddi-
tions and 1,3 dipolar cycloadditions with hydrazones have been
turned into a valuable tool for the synthesis of azetidinones and
pyrazoles respectively [8,9]. Hydrazones having an azomethine
proton CH
N NH constitute an important class of compounds
for new drug development [10–14]. They are mainly used as
∗ Corresponding author. Mobile: +91 9451308205.
E-mail address: rnsvk.chemistry@gmail.com (R.N. Singh).
1
386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2012.02.086

2
96
R.N. Singh et al. / Spectrochimica Acta Part A 92 (2012) 295–304
Fig. 1. The optimized geometries of the reactants and products involved in chemical reaction calculated at B3LYP/6-31G(d,p) level.
and characterized. In the present paper we report the dimer
structure of EFDMPCT using quantum chemical calculations and
experimental FT-IR spectrum. Further, other results – optimized
geometry, detailed spectroscopic analysis and chemical reactivity
of the title compound – are also being reported.
and 0.001200 were used in the calculations. The time depen-
dent density functional theory (TD-DFT) was carried out to find
the electronic transitions. The optimized geometrical parameters
were used in the vibrational frequency calculation to characterize
all stationary points as minima and all the harmonic vibrational
wavenumbers were found to be positive. All molecular structures
were visualized using software Chemcraft [39] and Gauss-View
2
. Experimental
[
40]. Potential energy distribution along internal coordinates was
calculated by Gar2ped software [41]. Internal coordinate system
recommended by Pulay et al. was used for the assignment of vibra-
tional modes [42].
All the chemicals used were of analytical grade. The solvent
methanol was dried and distilled before use according to the
standard procedure [32]. Ethyl-4-acetyl-3,5-dimetyl-1H-pyrrole-
2
2
-carboxylate was prepared by an earlier reported method [33].
,4-Dinitrophenylhydrazine was purchased from S.D. Fine. The 1
H
4
. Results and discussion
NMR spectrum of EDPHEDPC was recorded in DMSO-d6 on Bruker
DRX-300 spectrometer using TMS as an internal reference. The
4.1. Thermodynamic properties
−
5
UV–vis absorption spectrum of EDPHEDPC (1 × 10 M in DMSO)
was recorded on ELICO SL-164 spectrophotometer. The FT-IR-
spectrum was recorded in KBr medium on a Bruker-spectrometer.
The DART-Mass spectrum was recorded on JEOL-Acc TDF JMS-
T100LC, Accu TOF mass spectrometer.
The optimized geometries of all the reactants and products
involved in chemical reaction is shown graphically in Fig. 1,
calculated at B3LYP/6-31G(d,p) level. For sake of simplicity reac-
tants ethyl-4-acetyl-3,5-dimetyl-1H-pyrrole-2-carboxylate, 2,4-
dinitrophenylhydrazine and product EDPHEDPC and water are
abbreviated as A, B, C and D respectively. The vibrational frequency
calculations for all reactants and products were performed to deter-
mine the thermodynamic quantities at room temperature and their
values are listed in (Supplementary Table) TS1. For overall reaction
the enthalpy change of reaction (ꢁHReaction), Gibbs free energy
change of reaction (ꢁGReaction) and entropy change of reaction
2
.1. Synthesis of ethyl-4-{[(2,4-dinitrophenyl)-hydrazono]-
ethyl}-3,5-dimethyl-1H-pyrrole-2-carboxylate
(
EDPHEDPC)
A ice cold mixture of ethyl-4-acetyl-3,5-dimetyl-1H-pyrrole-2-
carboxylate (0.100 g, 0.5122 mmol), 2,4-dinitrophenyl hydrazine
0.1014 g, 0.5122 mmol) and two drop of HCl as catalyst in 30 ml
(
(
ꢁSReaction) are found to be −1.2525 kcal/mol, 3.0291 kcal/mol and
6.839 cal/mol-K respectively. The reaction has negative values for
HReaction and ꢁSReaction but positive value for ꢁGReaction indicat-
methanol was stirred for 12 h. After 12 h, the reaction mixture was
stirred again for 60 h at room temperature. A red color precipi-
tate was obtained. The precipitate was filtered off, washed with
methanol and dried in air. The yield is 60.74% and the compound
−
ꢁ
ing that the reaction is exothermic and non-spontaneous at room
temperature.
Total energy of the dimer is calculated as −2768.42575645 a.u.
at B3LYP/6-31G(d,p) level. The binding energy of dimer is computed
as the difference between the calculated total energy of the dimer
and the energies of the two isolated monomers and found to be
◦
decomposes above 218 C without melting.
3
. Computational details
−
14.52 kcal/mol. The calculated hydrogen binding energy of dimer
formation has been corrected for the basis set superposition error
(BSSE) via the standard counterpoise method [43] and found to be
All the calculations of the synthesized compound were carried
out with Gaussian 03 program package [34] to predict the molec-
1
ular structure, H NMR chemical shifts, vibrational wavenumbers
−10.35 kcal/mol.
and energies of the optimized structures using density functional
theory (DFT), B3LYP functional and 6-31G(d,p) basis set. B3LYP
invokes Becke’s three parameter (local, non local, Hartree–Fock)
hybrid exchange functional (B3) [35] with Lee–Yang–Parr cor-
relation functional (LYP) [36]. The basis set 6-31G(d,p) with ‘d’
polarization functions on heavy atoms and ‘p’ polarization func-
tions on hydrogen atoms are used for better description of polar
bonds of nitro group [37,38]. It should be emphasized that ‘p’
polarization functions on hydrogen atoms are used for reproducing
the out of plane vibrations involving hydrogen atoms. Conver-
gence criterion in which both the maximum force and displacement
smaller than the cut-off values of 0.000450 and 0.001800 and r.m.s.
force and displacement less than the cut-off values of 0.000300
The calculated changes in thermodynamic quantities dur-
ing the dimer formation in gaseous phase have the values ꢁH
(
−12.95 kcal/mol), ꢁG (−1.63 kcal/mol) and ꢁS (−37.98 cal/mol-K)
indicating that the dimer formation is exothermic and sponta-
neous. The calculated equilibrium constant using the formula
ꢁ
G = −RT ln K between monomer and dimer is quite high (K = 15.71)
indicating that dimer formation is highly preferred and as a result
even anti conformer gets converted to syn and finally forms
the dimer. The thermodynamics quantities (enthalpy, Gibbs free
energy, entropy), their change and equilibrium constant of conver-
sion from monomer to dimer are given in (Supplementary Table)
TS2.

R.N. Singh et al. / Spectrochimica Acta Part A 92 (2012) 295–304
297
Table 1
The selected optimized geometrical parameters of monomer (syn conformer) using
B3LYP/6-31G(d,p).
◦
◦
Bond length (Å)
Bond angle ( )
Dihedral angle ( )
R(1,2)
R(1,5)
R(1,28)
R(2,3)
R(2,9)
R(3,4)
R(3,8)
R(4,5)
R(4,7)
R(7,10)
R(9,12)
R(9,13)
R(10,11)
R(11,19)
R(11,35)
R(13,14)
R(14,15)
R(16,17)
R(16,21)
R(17,18)
R(18,19)
R(19,20)
R(20,21)
R(22,23)
R(22,24)
R(25,26)
R(25,27)
1.3821
A(2,1,28)
A(1,2,9)
A(2,3,8)
A(3,4,7)
A(1,5,6)
A(4,7,10)
A(4,7,44)
A(10,7,44)
A(3,8,32)
121.5071
116.0081
125.9323
127.67
D(1,2,9,13)
D(2,3,8,33)
D(3,4,7,10)
D(1,5,6,31)
D(4,7,10,11)
D(4,7,44,46)
D(2,9,13,14)
D(7,10,11,19)
D(10,11,19,20)
D(9,13,14,15)
D(13,14,15,38)
−179.423
−96.5741
146.4457
148.6313
176.782
118.8856
−179.871
178.6891
179.7639
−179.9919
179.7226
1.3523
1.0107
1.3915
1.4596
1.4359
1.5027
1.4071
1.4656
1.3001
1.2233
1.3506
1.3677
1.3568
1.0182
1.448
121.3019
116.9025
120.2683
122.7695
110.4775
122.4425
113.9611
123.5955
116.7331
120.7725
123.5018
115.7108
115.5283
107.5019
118.6365
118.8022
122.5613
117.9542
117.3846
124.6612
111.6514
A(2,9,12)
A(2,9,13)
A(12,9,13)
A(7,10,11)
A(10,11,19)
A(10,11,35)
A(19,11,35)
A(9,13,14)
A(13,14,15)
A(20,22,23)
A(20,22,24)
A(23,22,24)
A(16,25,26)
A(16,25,27)
A(26,25,27)
A(7,44,45)
D(21,16,17,41) −179.7182
D(17,16,21,43) 179.9061
D(17,16,25,26) −179.7765
D(16,17,18,42) −179.6326
D(17,18,19,11)
179.6913
1.516
D(11,19,20,21) −179.6561
D(19,20,21,43) 179.8898
D(19,20,22,24) −179.1823
1.4063
1.3807
1.3746
1.4227
1.432
1.3961
1.2495
1.2282
1.2320
1.2336
Table 2
The intermolecular hydrogen bonded geometrical parameters in dimer [bond length
◦
(
Å) and bond angle ( )].
X
H· · ·O
X
H
H· · ·O
X· · ·O
X
H· · ·O
N1 H28· · ·O86
N76 H82· · ·O12
C77 H83· · ·O12
C6 O86· · ·H29
1.02080
1.02081
1.09253
1.09252
1.89853
1.89801
2.60645
2.60378
2.87794
2.87758
3.46857
3.46938
159.73307
159.77263
135.23734
135.57715
methyl 4-p-tolyl-1H-pyrrole-2-carboxylate [45]. The N O bonds in
ortho–nitro group are more unsymmetrical due to the formation of
intramolecular hydrogen bond (N11 H35· · ·O23· · ·N22). This is not
only observed in our geometry but also reported in crystal structure
of hydrazones [46].
Fig. 2. The optimized geometries of ground state syn and anti conformers using
B3LYP/6-31G(d,p).
4.2. Molecular geometry
The calculated ground state syn and anti conformers of
the product ethyl-4-{[(2,4-dinitrophenyl)-hydrazono]-ethyl}-3,5-
dimethyl-1H-pyrrole-2-carboxylate are shown in Fig. 2. They have
energy −1384.20131188 and −1384.20075305 a.u. respectively at
room temperature with energy difference 0.35067 kcal/mol and
supposed to exist in ratio 65.4:34.6 respectively in the gas phase as
per Boltzmann distribution. But the syn conformer has geometrical
suitability for intermolecular hydrogen bonding by having pyrrolic
NH and ester CO on same side and their role lie in molecular asso-
ciation resulting into dimer. The geometrical parameter of the syn
conformer is given in Table 1 and the bond length and bond angle
of intermolecular hydrogen bonds formed in the dimer product
are given in Table 2. The geometrical parameter of the anti con-
former are given in (Supplementary Table) TS3 for the information.
The optimized geometry of dimer is shown in Fig. 3, with atomic
numbering.
The asymmetry of the N1 C2 and N1 C5 bonds can be
explained by electron withdrawing character of the ethoxycar-
bonyl group and conjugation of the N1 C5 with C4 C3 C2
skeleton. It leads to the elongation of N1 C2 bond. These effects
are not only in quantum calculation but also reflect in crystal
structure of the ethyl-3,5-dimethyl-1H-pyrrole-2-carboxylate [44],
Fig. 3. The optimized geometry of dimer for lower energy ground state syn-
conformer using B3LYP/6-31G(d,p).

2
98
R.N. Singh et al. / Spectrochimica Acta Part A 92 (2012) 295–304
Table 3
Experimental and theoretical 1H NMR chemical shifts using B3LYP/6-31G(d,p) in
0.30
.25
◦
DMSO-d6 as the solvent (25 C).
0
Atom no.
ıexp
ıcalcd
H28
H29
H30
H31
H32
H33
H34
H35
H36
H37
H38
H39
H40
H41
H42
H43
H45
H46
H47
10.2
7.85377
0.20
0.15
0.10
1.35077
1.88487
1.96757
2.49717
1.61427
1.33487
11.2851
3.70727
3.72217
0.54707
0.90417
0.87727
7.76177
7.38567
8.78657
1.84307
1.56107
1.52147
2.42
2.48
0
0
.05
.00
11.73
4.23
2
00
300
400
500
600
700
800
1.29
Wavelength/nm
8.3
7.8
8.56
Fig. 4. Experimental UV–vis spectrum of EDPHEDPC.
Frontier molecular orbitals (FMOs), HOMO and LUMO plot are given
in Supplementary Fig. 1. The highest occupied molecular orbital
3.77
(HOMO) and lowest unoccupied molecular orbital (LUMO) are very
popular quantum chemical parameters. The FMOs are important
in determining molecular reactivity and the ability of a molecule
to absorb light. The vicinal orbitals of HOMO and LUMO play the
same role of electron donor and electron acceptor respectively.
The energies of HOMO and LUMO and their neighboring orbitals
In dimer, two hydrogen bonds are formed by heteronuclear
intermolecular hydrogen bonding (N H· · ·O C) between pyrrolic
(
N H) and carbonyl (C O) of ester. In intermolecular hydrogen
bonds, the N H bond acts as proton donor and C O bond as proton
acceptor. According to the Etter terminology [47], the cyclic ester
are
all negative, which indicate the title molecule is stable [49].
The HOMO–LUMO energy gap is an important stability index. The
HOMO–LUMO
2
dimer form the ten-membered pseudo ring denoted as R2 (10) or
2
more extended sixteen-membered pseudo ring R2 (16) including
energy gap of title molecule reflects the chemical
stability of the molecule.
pyrrole ring. The superscript designates the number of acceptor
centers whereas the subscript designates the number of donors
HOMO energy = −5.8864 eV
LUMO energy = −2.764 eV
in the motif. In dimer both proton donor (N H bond) and pro-
ton acceptor (C O bond) are elongated by 0.0101 A˚ and 0.0091 A˚
respectively.
4
.3. 1H NMR spectroscopy
HOMO–LUMO energy gap = 3.1228 eV
The geometry of the title compound, together with that of
tetramethylsilane (TMS) is fully optimized. H NMR chemical shifts
are calculated with GIAO approach using B3LYP method and 6-
1G(d,p) basis set [48]. Chemical shift of any X proton (CSX) is
equal to the difference between isotropic magnetic shielding IMS
of (TMS) and proton (X). It is defined by an equation written
TD-DFT calculations using B3LYP/6-31G(d,p), predict three
intense electronic transitions at ꢂmax = 298.79 nm, f = 0.2718;
ꢂmax = 267.21 nm, f = 0.1775 and ꢂmax = 243.48 nm, f = 0.4128 are in
agreement with the experimental electronic transitions at ꢂmax
288, 242 and 227 nm respectively. The calculated values for wave-
length of maximum absorption (ꢂmax) are also in agreement with
the reported ꢂmax in literature [50]. According to the TD-DFT calcu-
lations, the experimental band at 288, 242 and 227 nm originates
mainly due to the H−2 → L+1, H−5 → L and H−1 → L+3 transitions
respectively. On the basis of calculated molecular orbital coeffi-
1
3
as [CSX = IMS
− IMSX]. The experimental and calculated values
TMS
1
of H NMR chemical shifts of the title compound are given in
Table 3. The value of correlation coefficient (R = 0.9545) between
2
experimental and calculated chemical shifts show that there is a
good agreement between them. The chemical shift of proton H35
appeared at 11.73 ppm due to deshielding which is consequence of
the intramolecular hydrogen bond N11 H35· · ·O23· · ·N22.
*
*
cient analysis, these electronic excitations show ␲ → ␲ , n → ␲ and
*
␲ → ␲ transitions.
4.5. Vibrational assignments
4.4. UV–vis spectroscopy
The experimental and calculated vibrational wavenumbers of
The nature of the transitions observed in the UV–vis spectrum
dimer at B3LYP/6-31G(d,p) level and their assignments using
PED are given in Table 5 . The calculated (monomer, dimer)
and the experimental FT-IR spectra of EDPHEDPC in the region
4000–400 cm are shown graphically in Supplementary Fig. 2. The
total number of atoms in monomer and dimer are 49 and 98
of EFDMPCT has been studied by the time dependent density func-
tional theory (TD-DFT). The observed and calculated electronic
transitions of high oscillatory strength are listed in Table 4. Exper-
imental UV–vis spectrum of the title compound is shown in Fig. 4.
−
1
Table 4
◦
Comparison between experimental and calculated electronic transitions: energy, oscillatory strength, ꢂmax (nm) using TD-DFT/B3LYP/6-31G(d,p) in DMSO at 25 C.
S. no.
Orbital transitions
Energy (eV)
Oscillatory strength, f
Calculated ꢂmax
Observed ꢂmax
% contribution
Assignment
1
2
3
4
H−1 → L + 1
H−2 → L + 1
H−5 → L
3.3993
4.1496
4.6399
5.0921
0.1878
0.2718
0.1775
0.4128
364.74
298.79
267.21
243.48
48.94
31.65
35.57
40.52
*
288
242
227
␲ → ␲
*
n → ␲
*
H−1 → L + 3
␲ → ␲

R.N. Singh et al. / Spectrochimica Acta Part A 92 (2012) 295–304
299
Table 5
Experimental and calculated (selected) vibrational wavenumbers (cm 1) of dimer using B3LYP/6-31G(d,p) with assignments [IRint (Kmmol−1)].
−
Mode no.
Wavenumbers
Unscaled
IRint
Experimental wavenumbers
Assignment (PED) ≥ 5%
Scaled
276
275
274
273
271
260
264
258
3480
3480
3467
3461
3269
3141
3160
3133
3343
3343
3331
3325
3140
3017
3036
3010
67.49
3426
3269
␯(N61 H65)(99)
␯(N11 H35)(99)
␯(N1 H28)(50)–␯(N76 H82)(48)
␯(N76 H82)(51)–␯(N1 H28)(49)
␯(C53 H57)(83)–␯(C21 H43)(16)
␯(C89 H93)(28)–␯(C89 H94)(23), ␯(C15 H39)(19)–␯(C15 H40)(16)
␯(C8 H32)(79)–␯(C8 H34)(19)
66.71
2872.82
11.88
42.26
55.66
2983
11.06
45.15
␯(C89 H92)(38)–␯(C15 H38)(24)–␯(C89 H94)(12)–␯(C89 H93)(8),
␯
(C15 H40)(8), ␯(C15 H39)(5)
␯(C7 C44)(20)–␯(C6 H31)(18),
(C77 H84)(17)–␯(C77 H85)(15)–␯(C77 H83)(13)–␯(C6 H29)(12)
2
56
3115
2992
17.05
␯
254
253
252
3111
3111
3106
2989
2989
2984
19.14
15.14
12.22
2921
␯(C75 H81)(61)–␯(C75 H80)(19), ␯(C75 H80)(12), ␯(C8 H34)(5)
␯(C8 H34)(61)–␯(C8 H33)(19), ␯(C8 H32)(12)–␯(C75 H81)(5)
␯(C88 H91)(40)–␯(C88 H90)(33), ␯(C14 H37)(6),
␯(C89 H94)(6)–␯(C89 H93)(5)–␯(C14 H36)(5)
2
2
48
45
3063
3058
2942
2938
55.62
31
␯(C14 H36)(29), ␯(C14 H37)(24)–␯(C88 H90)(24)–␯(C88 H91)(20)
␯(C15 H38)(19), ␯(C15 H40)(18),
␯(C15 H39)(17)–␯(C89 H92)(16)–␯(C89 H94)(15)–␯(C89 H93)(4)
244
243
241
238
236
3053
3053
3040
1724
1671
2933
2933
2920
1656
1605
10.25
15.96
43.23
1932.14
363.74
␯(C7 C44)(57), ␯(C6 H29)(21), ␯(C6 H31)(18)
2853
1664
␯(C77 H84)(48), ␯(C77 H83)(23), ␯(C77 H85)(15)
␯(C8 H33)(43)–␯(C75 H80)(37), ␯(C8 H34)(7)–␯(C75 H81)(6)
␯(C9 O12)(26)–␯(C78 O86)(25), ␦(C9C14O13)(13)–␦(O12C9O13)(11)
␯(C17 C18)(10), ␯(C52 C54)(10), ␯(C20 C21)(6),
␯
(C53 C56)(6)–␯(C16 C21)(6)–␯(C50 C53)(6)
␯(C52 C54)(9)–␯(C17 C18)(9),
(C53 C56)(6)–␯(C20 C21)(6)–␯(C50 C53)(6), ␯(C16 C21)(6)
2
35
1670
1604
804.68
1619
1565
␯
233
231
230
1653
1643
1624
1588
1578
1560
1148.71
18.46
16.48
␯(N25 O27)(11)–␯(N49 O51)(10)–␯(N25 O26)(10), ␯(O48 N49)(10)
␯(N64 C66)(26)–␯(C7 N10)(26)
␯(N60 O63)(13), ␯(N22 O24)(12), (␦-N64H65N61)(10),
(
␦-N10H35N11)(10)–␯(N60 O62)(7)–␯(N22 O23)(7)
␯(N22 O24)(13)–␯(N60 O63)(12),
␦-N10H35N11)(10)–(␦-N64H65N61)(10)–␯(N22 O23)(7), ␯(N60 O62)(7)
2
29
1624
1560
18.41
(
2
2
2
28
27
26
1607
1600
1597
1544
1537
1534
36.19
523.47
16.58
R(␦-C2H28N1)(29), (␶-O86H28)(15)–R(␦-C70H82N76)(7)
R(␦-C2H28N1)(24), (␶-O86H28)(13), R(␦-C70H82N76)(6)
␯(N49 O51)(7), ␯(N25 O27)(7)–␯(C50 C53)(7)–␯(C16 C21)(7),
1511
1449
␯(N60 O63)(6)–␯(O48 N49)(6),
␯(N22 O24)(6)–␯(N25 O26)(6)–␯(N60 O62)(5)–␯(N22 O23)(5)
2
25
1596
1533
31.92
␯(N25 O27)(6)–␯(N49 O51)(6)–␯(C16 C21)(6), ␯(C50 C53)(6),
(N22 O24)(5)–␯(N60 O63)(5)–␯(N25 O26)(5), ␯(O48 N49)(5)
␯
224
223
222
220
1565
1564
1557
1535
1503
1502
1495
1474
55.8
␯(N11 C19)(9), ␯(C58 N61)(9), ␯(C16 C17)(8), ␯(C50 C52)(8)
␯(C58 N61)(10)–␯(N11 C19)(10), ␯(C50 C52)(9)–␯(C16 C17)(9)
761.66
256.39
16.28
ꢂ
ꢂ
ꢂ
ꢂ
(␦as-Me2 )(21), (␶-H82012)(15), (␶-H84C14)(7)–(␳-Me2 )(7)–(␶-C70C77)(6)
(␦as-Me2 )(39), (␶-H82012)(16)–(␶-C70C77)(8)–(␳-Me2 )(5),
␦sc-C88H90H91)(5)
(␶-H84C14)(34), (␦sc-H36H37C14)(14), (␦as-Me1)(7), (␶-C15C14)(6),
(
219
218
217
216
1535
1529
1529
1519
1474
1469
1469
1459
20.1
(
␻-H36H37C14)(5)
ꢂ
11.56
54.61
48.39
(␦as-Me2 )(25), (␶-H82012)(9)–(␶-H84C14)(6)–(␦sc-H36H37C14)(6)–(␦as-
Me )(6)–(␶-C70C77)(5)–(␶-C15C14)(5)
(␦as-Me2 )(19), (␶-H84C14)(16), (␶H82012)(8), (␶-O86H28)(6),
ꢂ
ꢂ
(
␦sc-H36H37C14)(6), (␶-C15C14)(5)
ꢂ
(␦as-Me2 )(28), (␶-H82012)(13)–(␶-C70C77)(10),
(
(␦as-Me2 )(36), (␶-H82012)(14)–(␶-C70C77)(12)–(␦as-Me3 )(6)
(␦as-Me2 )(25)–(␶-C15C14)(9), (␶-H82012)(8)–(␶-C70C77)(8),
ꢂ
␦as-Me3)(7)–(␦as-Me3 )(5)–(␦as-Me1)(5)
ꢂ
ꢂ
ꢂ
2
2
15
12
1518
1509
1458
1449
55.22
11.41
(
␦as-Me1)(6)–(␶-C5C6)(5)
ꢂ
ꢂ
2
11
1509
1449
25.88
(␦as-Me2 )(34), (␶-H82012)(13)–(␶-C70C77)(13), (␶-O86H28)(7)–(␦as-Me )(6),
(
␶-C89C88)(5)
ꢂ
ꢂ
210
209
207
206
205
1504
1504
1500
1495
1494
1445
1445
1441
1436
1435
10.24
25.96
11.59
74.58
19.21
(␦as-Me2)(12), (␦as-Me1 )(11)–(␦as-Me3)(8), (␶-O86H28)(7)–(␦as-Me3 )(6)
(␦as-Me1 )(13)–(␦as-Me2)(11)–(␦as-Me3 )(8), (␦as-Me3)(7)
(␦as-Me )(54), (␶-H30C89)(16)–(␶-O86H28)(13)–(␶-C15C14)(5)
(␦as-Me2 )(45)–(␦as-Me1)(7), (␶-H82012)(6)
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
(␶-C70C77)(17)–(␶-O86H28)(9), (␦as-Me2 )(8)–(␦as-Me2 )(6)–(␦s-Me2 )(6),
ꢂ
ꢂ
(
␳-Me2 )(5)–(␶-H84C14)(5)–(␳-Me2 )(5)
ꢂ
ꢂ
203
201
199
198
197
1493
1485
1477
1472
1472
1434
1426
1419
1414
1414
96.81
14.6
454.57
22.29
214.34
(␦as-Me2 )(64), (␶-H82012)(17)–(␶-C70C77)(10)
(␦as-Me2 )(54), (␶-H82012)(17)–(␶-C70C77)(12)
1382
(␶-C70C77)(12)–(␶-O86H28)(9)
(␶-H84C14)(22)–(␶-C70C77)(16), (␶-H30C89)(9), (␶-O86H28)(7)–(␶-C5C6)(5)
(␶-O86H28)(21)–(␶-C70C77)(14)–(␶-H30C89)(8)–(␶-H82012)(7),
(
␶-H84C14)(5)–(␻-H36H37C14)(5)
ꢂ
1
95
93
1467
1437
1409
1380
70.76
17.42
(␦as-Me2 )(19)–(␶-C70C77)(10)–␯(C53 C56)(9), ␯(C52 C54)(8),
␯
(C20 C21)(7)–␯(C17 C18)(6), (␶-H82012)(6)
ꢂ
1
(␶-H84C14)(26), (␻-H36H37C14)(12)–(␶-H82012)(12)–(␦s-Me2 )(12)–(␦s-
Me)(8)–(␶-H30C89)(8),
(
␦s-Me1)(5)

3
00
Table 5 (Continued)
Mode no. Wavenumbers
R.N. Singh et al. / Spectrochimica Acta Part A 92 (2012) 295–304
IRint
Experimental wavenumbers
Assignment (PED) ≥ 5%
Unscaled
Scaled
ꢂ
190
188
187
186
1427
1417
1417
1403
1371
1361
1361
1348
66.51
(␶-H82012)(26), (␦s-Me2 )(24)–(␶-O86H28)(18)–(␦s-Me1)(12)–(␶-H84C14)(7)
(␦s-Me3)(76), ␯(C7 C44)(5)
12.89
19.71
33.99
ꢂ
(␦s-Me3 )(78), ␯(C66 C68)(5)
(␦as-Me2 )(17)–(␶-C70C77)(16)–(␻-H36H37C14)(6),
ꢂ
(
␶-C5C6)(5)–(␶-H30C89)(5)
ꢂ
182
181
180
179
1389
1388
1382
1382
1334
1333
1327
1327
142.55
436.63
475.45
1037.86
(␻-H36H37C14)(16), (␶-C70C77)(10)–(␦as-Me2 )(10), (␶-H84C14)(5)
(␻-H36H37C14)(16), (␶-H84C14)(15)–(␶-C70C77)(11), (␦as-Me2 )(9)
(␻-H36H37C14)(10), (␶-C70C77)(9)–(␦as-Me2 )(7)
ꢂ
ꢂ
1285
(␻-H36H37C14)(9), (␶-H84C14)(8)–(␶-C70C77)(8),
ꢂ
(
␦as-Me2 )(6)–␯(N49 O51)(5), ␯(N25 O27)(5)
1
78
1357
1303
174.03
␯(C56 C58)(10),
␯
␯
(C50 C53)(7)–␯(N60 O63)(6)–␯(N60 O62)(6)–␯(C54 C58)(6),
(C19 C20)(6)
177
176
175
174
173
1357
1326
1324
1311
1310
1303
1274
1272
1259
1258
291.7
14.34
933.29
84.59
346.19
␯(C19 C20)(10),
(C16 C21)(7)–␯(N22 O24)(6)–␯(N22 O23)(6)–␯(C18 C19)(6)–␯(C56 C58)(6)
(␻-H36H37C14)(17),
␶-H84C14)(15)–R(␦-C2H28N1)(9)–(␶-O86H28)(9)–(␶-C70C77)(8)
(␻-H36H37C14)(18)–R(␦-C2H28N1)(11), (␶-H84C14)(9),
␶-C70C77)(8)–(␶-O86H28)(8), ␦(O12C9O13)(5)
␯(N22 O23)(6), ␯(N60 O62)(5), (␶-O86H28)(5),
R(␦-C2H28N1)(4)–␯(C20 N22)(3)
(␶-H84C14)(6)–(␶-H82012)(6)–R(␦-C2H28N1)(5),
␯
(
1230
(
␯(N60 O62)(5)–␯(N22 O23)(5)
1
1
69
68
1288
1248
1237
1199
431.71
18.21
(␶-H82012)(8)
R1(␦-C19H42C18)(8)–R1(␦-C52H59C54)(8), R1(␦-C16H43C21)(6),
R1(␦-C50H57C53)(6)
167
166
165
162
161
1248
1242
1240
1163
1163
1199
1193
1191
1117
1117
75.67
14.36
R1(␦-C52H59C54)(9), R1(␦-C19H42C18)(9)–R1(␦-C50H57C53)(7),
R1(␦-C16H43C21)(7)
␦(O12C9O13)(13), R(␦-C2H28N1)(9), (␻-H36H37C14)(9), ␯(N1 C2)(7),
(
␶-O86H28)(7), (␶-H84C14)(7), ␯(C74 N76)(7)–␯(C9 O13)(5)
582.47
13.29
1191
(␶-O86H28)(15), R(␦-C2H28N1)(12), ␦(O12C9O13)(11), (␻-H36H37C14)(7),
␯
(N1 C2)(7)–␯(C74 N76)(7)–␯(C9 O13)(5), ␯(C78 O87)(5)
ꢂ
(␦-R1)(8)–(␦-R1 )(7), ␯(C16 N25)(7), ␯(N49 C50)(6), ␯(C20 N22)(6),
␯
(C56 N60)(5), ␯(N10 N11)(5)
ꢂ
103.78
(␦-R1 )(8), (␦-R1)(7)–␯(N49 C50)(7),
␯
␯
(C16 N25)(6)–␯(C56 N60)(6)–␯(N61 N64)(5), ␯(C20 N22)(5),
(N10 N11)(5)
1
60
59
1157
1156
1111
1110
17.37
R1(␦-C18H41C17)(15)–R1(␦-C50H55C52)(13)–R1(␦-C19H42C18)(9),
R1(␦-C52H59C54)(7)–␯(N10 N11)(6)–␯(N61 N64)(5)
R1(␦-C50H55C52)(16),
1
309.86
R1(␦-C18H41C17)(13)–R1(␦-C52H59C54)(9)–R1(␦-C19H42C18)(7),
␯
(N61 N64)(5)
ꢂ
1
1
1
1
1
58
57
56
55
54
1146
1146
1138
1137
1127
1101
1101
1093
1092
1082
337.8
50.88
267.92
65.13
27.35
1101
(␶-O86H28)(17)–(␳-Me )(10), (␶-C15C14)(9), (␦sc-H36H37C14)(8),
␦
(C9C14O13)(7), (␳-Me)(5), (␶-C89C88)(5)
ꢂ
(␶-O86H28)(19), (␳-Me )(11), (␶-C15C14)(8), (␦sc-H36H37C14)(8),
␦(C9C14O13)(7)–(␶-C89C88)(6), (␳-Me)(5)
ꢂ
(␶-O86H28)(21)–(␳-Me )(14), (␶-C15C14)(11), (␶-C89C88)(8), ␦(C9C14O13)(7),
(
␳-Me)(7), (␦sc-H36H37C14)(6)
ꢂ
(␶-O86H28)(20), (␳-Me )(15), (␶-C15C14)(11)–(␶-C89C88)(8), ␦(C9C14O13)(7),
(
␳-Me)(7), (␦sc-H36H37C14)(6)
(␶-O86H28)(8), ␯(N10 N11)(7), ␯(N61 N64)(7), (␳-Me )(6), (␶-C15C14)(5),
␶-H82012)(5)
ꢂ
(
ꢂ
ꢂ
1
52
50
1090
1080
1047
1037
19.3
32.14
(␶-H82012)(13), (␳-Me3)(12)–(␳-Me3 )(8)–(␳-Me2 )(8), (␶-C70C77)(5)
R1(␦-C16H43C21)(13), ␯(C20 N22)(10), (␦-R1)(9), ␯(C16 C17)(6),
1
␯
(C16 C21)(5)
ꢂ
1
49
1080
1037
39.4
R1(␦-C50H57C53)(12)–(␶-H82012)(11), ␯(C56 N60)(9)–(␦-R1 )(8),
ꢂ
ꢂ
(
␳-Me2 )(7), ␯(C50 C52)(6)
1
1
1
47
44
41
1064
1057
1048
1022
1015
1006
12.74
13.32
77.65
(␳-Me2 )(22), (␶-H82012)(20)–(␶-C70C77)(12), (␶-H84C14)(9), (␶-O86H28)(8)
(␶-H82012)(39)–(␳-Me2 )(17), (␳-Me2 )(5)
␯(C88 C89)(10)–␯(C14 C15)(10),
ꢂ
ꢂ
1023
884
ꢂ ꢂ
(O13 C14)(10)–␯(O87 C88)(9)–(␶-H84C14)(8), (␳-Me2 )(7), (␳-Me )(6)
␯
ꢂ
134
133
132
130
989
989
967
944
950
950
929
906
110
18.83
9.44
␯(C7 C44)(16)–␯(C66 C68)(13), (␳-Me3)(11)–(␳-Me3 )(8)
␯(C66 C68)(16), ␯(C7 C44)(12), (␳-Me3 )(10), (␳-Me3)(8)
ꢂ
R1(␻-C21H43)(77), (R1-puckering)(10)
␯(C16 N25)(8), ␯(N49 C50)(7)–␯(C20 N22)(7)–␯(C56 N60)(6), (␦-R1)(5),
10.07
(
␦-R1)(5)
1
29
27
944
905
906
869
30.41
18.28
␯(N49 C50)(8)–␯(C16 N25)(7)–␯(C56 N60)(7), ␯(C20 N22)(6),
ꢂ
ꢂ
(
␦-R1 )(5)–(␦-R1 )(5)
(␶-O86H28)(18)–(␳-Me )(12), (␻-H36H37C14)(8), (␶-C15C14)(6), (␳-Me)(6),
␶-H84C14)(6), ␯(O13 C14)(5), (␶-C89C88)(5), (␶-H82012)(5)
ꢂ
1
(
ꢂ
1
1
22
21
862
862
828
828
14.75
13.38
R1(␻-C54H59)(46), R1(␻-C52H55)(22)–R1(␻-C58N61)(8)–(␶-R1 )(6)
R1(␻-C18H42)(46), R1(␻-C17H41)(22), R1(␻-C19N11)(8), (␶-R1)(6)

R.N. Singh et al. / Spectrochimica Acta Part A 92 (2012) 295–304
301
Table 5 (Continued)
Mode no. Wavenumbers
IRint
Experimental wavenumbers
Assignment (PED) ≥ 5%
Unscaled
841
Scaled
808
1
19
50.85
829
776
662
(␦-O27O26N25)(19)–(␦-O51O48N49)(18),
ꢂ
(
␦-O23O24N22)(15)–(␦-O62O63N60)(14)–(␦-R1)(6)–(␦-R1 )(6)
118
110
106
829
758
746
796
728
716
114.24
15.44
24.1
(␻-N1H28)(51)–(␶-O86H28)(47)
(␶-O86H28)(16)–(␻-N1H28)(14)
R1(␻-C50N49)(16), R1(␻-C16N25)(14),
ꢂ
(
R1 -puckering)(11)–(R1-puckering)(9)–R1(␻-C56N60)(5)
1
05
03
746
719
716
690
21.57
10.77
(␻-C9C2)(20), R1(␻-C16N25)(9), (␻-C2C9)(9)–R1(␻-C50N49)(8),
ꢂ
(
␻-N1H28)(7), (␻-C74C78)(7)–(R1-puckering)(6)–(R1 -puckering)(5)
ꢂ
1
(␻-N1H28)(15), (␶-C70C77)(13), (␶-R)(13)–(␶-R )(10), (␻-C5C6)(9),
(
␶-R)(8)–(␻-C70C77)(6), (␶-H82012)(6)
9
9
8
5
664
647
637
621
35.98
63.41
(␶-R)(21), (␻-N1H28)(12)–(␦-R1)(7), (␻-C2C9)(6)–(␶-C9C2)(6)–(␦-R1)(5)
(␻-N61H65)(14), (␶-H82012)(13), (␻-N11H35)(11)–(␶-R)(8)–(␻-N1H28)(6),
627
(
␶-C70C77)(6)
(␻-C2C9)(28), (␶-R)(15)–(␶-C9C2)(13)–(␻-C74C78)(8),
␻-N1H28)(7)–(␻-C9C2)(6)
(␶-R)(19), (␻-C2C9)(17)–(␶-C9C2)(12),
␻-N1H28)(10)–(␻-C74C78)(7)–(␻-C9C2)(7)
9
4
0
641
632
615
607
49.36
15.27
(
9
(
8
7
4
9
536
478
514
459
15.89
35.27
(␳-C16N25)(22)–(␦-O51C50N49)(22)
(␶-H82012)(14), R(␦-C67C77C70)(10), (␶-C70C77)(7), (␻-N1H28)(7),
476
␦(O12C9O13)(5)
7
3
421
404
13.82
(␶-H82012)(17)–(␦sc-H36H37C14)(14), (␶-O86H28)(12)–(␻-C2C9)(10)
ꢂ
ꢂ
␯
, stretching; ␦sc, scissoring; ␳, rocking; ␻, wagging; t, twisting; ␦ and ␦ , deformation; ␦ as, asymmetric deformation; ␶, torsion. R, pyrrole ring; R1, benzene ring.
calculated wavenumber at 3018, 2933 and 2989 cm 1 respec-
−
respectively, which gives 141 and 288, (3n − 6) vibrational modes
for monomer and dimer respectively. The calculated vibrational
wavenumbers are higher than their experimental values for the
majority of the normal modes. The vibrational frequency usu-
ally is overestimated in DFT due to two factors: (1) the overall
neglect of anharmonicity and (2) an incomplete description of
electron correlation due to the use of an incomplete basis set. There-
fore, calculated wavenumbers at B3LYP/6-31G(d,p) level are scaled
down using single scaling factor 0.9608 [51], to discard the anhar-
monicity present in real system. The observed wavenumbers are in
good agreement with the calculated wavenumbers of dimer than
monomer. Therefore, observed wavenumbers are assigned using
dimer PED. The monomers as well as the dimer possess C1 symme-
try; therefore the vibrational modes will be active for both IR and
Raman. The Raman spectrum of the compound was calculated and
found equal in frequencies and intensities.
tively. A combination band of Me-rocking and CH -scissoring
observed at 1101 cm agrees well with the calculated wavenum-
ber at 1110 cm . The observed rocking mode of Me and Me2
2
−
1
−
1
−
1
at 1023 cm
corresponds to the calculated wavenumber at
1007 cm−1. The CH2 wagging mode is observed at 1285 cm
−1
,
−
1
whereas it is calculated as 1328 cm
.
4.5.3. C O vibrations
The stretching mode of carbonyl group (␯
) is observed at
O
C
−
1
−1
1664 cm , whereas it is calculated as 1655 cm
in dimer and
in monomer. The observed ␯C O absorption band at
is in good agreement with the calculated wavenum-
−
−
1
1
1692 cm
1664 cm
ber of dimer. The observed ␯C O also agrees well with the earlier
−
1
reported wavenumber at 1665 cm for dimer of syn-pyrrole-2-
carboxylic acid [52]. Therefore, ␯C O stretching mode in EDPHEDPC
confirms the involvement of C O group in intermolecular hydro-
−
gen bonding. The observed C9 O13 stretching mode at 1191 cm
1
4.5.1. N H vibrations
−
1
In the experimental FT-IR spectrum of EDPHEDPC, the N
H
is observed at same wavenumber at 1191 cm
with 5% contri-
−
1
stretch of pyrrole (␯NH) is observed at 3269 cm , whereas it is
bution in dimer PED. The O12C9O13 deformation is observed at
−
1
−1
−1
−1
.
calculated as 3331 cm
in dimer and 3500 cm
in monomer.
1230 cm , whereas it is calculated as 1272 cm
−1
The observed wavenumber at 3269 cm
is in good agreement
with the calculated wavenumber of dimer. The observed value
4.5.4. N O vibrations
of ␯NH also correlates with the earlier reported strong absorp-
tion at 3358 cm for hydrogen bonded pyrrole-2-carboxylic acid
The molecule under investigation possesses two nitro groups.
The nitro groups show two type of stretching vibrations as
asymmetric and symmetric. Asymmetric stretching vibrations are
always observed at higher wavenumber than symmetric stretch-
ing vibrations. The observed asymmetric stretching vibrations
−1
recorded in KBr pellet, but it deviates to the reported free ␯NH
−1
band at higher wavenumber 3465 cm , recorded in CCl4 solution
52]. Therefore, solid state spectrum of EDPHEDPC attributes to the
vibration of hydrogen-bonded N H group. The observed N H wag-
[
−
1
of N O (␯N O) at 1565 cm
agrees well with the calculated
−1
−1
ging mode of pyrrole at 797 cm corresponds to the calculated
wavenumber at 1588 cm . Symmetric stretching vibration of ␯
N
O
wavenumber at 808 cm−1. The observed N H deformation of pyr-
−1
−1
is observed at 1285 cm , whereas it is calculated as 1328 cm . The
−
1
−1
role at 1537 cm agrees well with the calculated wavenumber at
observed NO2 deformation at 829 cm corresponds to the calcu-
lated wavenumber at 797 cm . The observed wavenumbers are
−
1
−1
1
3
536 cm . The hydrazide N H stretching vibration is observed at
426 cm , whereas it is calculated as 3340 cm .
−
1
−1
in agreement with the earlier reported wavenumbers for asym-
−
1
metric and symmetric vibration of nitro group at 1600 cm and
−
1
4.5.2. C H vibrations
1319 cm respectively [53].
Four methyl groups are present in the molecule. They are
abbreviated as Me, Me1, Me2 and Me3. Me1 and Me2 are
directly attached to the C5 and C3 carbon of pyrrole ring
4.5.5. C N and C C vibrations
The C19 N11 stretching vibration is observed at 1449 cm−1,
−
1
.
Me and Me3 are attached to the CH2 of ester and C7 carbon
whereas it is calculated as 1503 cm . The observed C16 N25 wag-
−
1
respectively. The observed stretching vibration of Me, Me1 and
ging mode at 662 cm corresponds to the calculated wavenumber
−1
−1
−1
Me2 at 2983, 2853 and 2921 cm
are in agreement with the
at 718 cm . The C N stretching vibration is assigned at 1579 cm

3
02
R.N. Singh et al. / Spectrochimica Acta Part A 92 (2012) 295–304
in dimer PED. The observed C C stretches in benzene ring at
rings are abbreviated as Ring1 and Ring2 respectively. The ε values
for bonds involved in Ring1 and Ring2 are given in (Supplementary
Table) TS5. In Ring1, the values of ε for bonds O12 C9, C9 C2,
C2 C3, C3 C4, C4 C5, C5 N1 associated with the N1 H28· · ·O86
and for bonds O86 C78, C78 C74, C74 C69, C69 C67, C67 C70,
C70 N76 associated with the N76 H82· · ·O12 are in the range
of 0.1006–0.2857. In Ring2, the values of ε for bonds O23 N22,
N22 C20, C20 C19, C19 N11 associated with the N11 H35· · ·O23
are in the range of 0.1130-0.2299. These values of ε correspond to
the aromatic bonds reported in literature [57]. The ε values confirm
the presence of resonance assisted intermolecular and intramolec-
ular hydrogen bonds in Ring1 and Ring2 of dimer.
−1
1
1
619, 1449 cm
605, 1503 cm
correspond to the calculated wavenumber at
respectively. The observed pyrrole ring defor-
−1
−1
mation at 1230 cm corresponds to the calculated wavenumber
at 1273 cm . Puckering mode of benzene ring is observed at
6
−
1
−
1
−1
62 cm , whereas it is calculated as 718 cm with 11% contri-
bution in dimer PED.
4
4
.6. AIM calculations
.6.1. ꢃ-Delocalization effect in resonance assisted intra and
intermolecular hydrogen bonds (RAHB) and topological
parameters
Geometrical as well as topological parameters are useful tool to
characterize the strength of hydrogen bond. The geometrical cri-
teria for the existence of hydrogen bond are as follows: (i) The
distance between proton (H) and acceptor (A) is less than the sum of
4
4
.7. Chemical reactivity
.7.1. Global reactivity descriptors
On the basis of Koopman’s theorem [58], global reactivity
their van der Waal’s radii of these atoms. (ii) The ‘donor (D)–proton
descriptors electronegativity (ꢄ), chemical potential (ꢅ), global
hardness (Á), global softness (S) and global electrophilicity index
◦
(
‘
H)· · ·acceptor (A)’ angle is greater than 90 . (iii) The elongation of
donor (D)–proton(H)’ bond length is observed.
(ω) are calculated using the energies of frontier molecular orbitals
As the above criteria are frequently considered as insufficient,
εHOMO, εLUMO and given by Eqs. (1)–(5) [59–62]
the existence of hydrogen bond could be supported further by Koch
and Popelier criteria [54] based on ‘Atoms in molecules’ theory: (i)
The existence of bond critical point for the ‘proton (H)· · ·acceptor
ꢄ = −(1/2)(εLUMO + εHOMO
)
(1)
(2)
(3)
(4)
ꢅ = −ꢄ = (1/2)(εLUMO + εHOMO
)
(
A)’ contact as a confirmation of the existence of hydrogen bond-
ing interaction. (ii) The value of electron density (ꢀ
be within the range of 0.002–0.040 a.u. (iii) The corresponding
) should
H· · ·A
Á = (1/2)(εLUMO − εHOMO
S = (1/2)Á
)
2
Laplacian ꢀ ꢀ
should be within the range of 0.024–0.139 a.u.
BCP
According to Rozas et al. [55], the interactions may be classified
2
ꢅ2
as follows: (i) Strong H-bonds are characterized by ꢀ ꢀ
< 0 and
BCP
ω =
(5)
H
BCP
< 0 and their covalent character is established. (ii) Medium
2Á
2
H-bonds are characterized by ꢀ ꢀ
partially covalent character is established. (iii) Weak H-bonds are
> 0 and HBCP < 0 and their
BCP
According to Parr et al., electrophilicity index (ω) is a global
reactivity index similar to the chemical hardness and chemical
potential. This is positive and definite quantity. This new reactiv-
ity index measures the stabilization in energy when the system
acquires an additional electronic charge (ꢁN) from the environ-
ment. The direction of the charge transfer is completely determined
by the electronic chemical potential of the molecule because an
electrophile is a chemical species capable of accepting electrons
from the environments. Therefore its energy must decrease upon
accepting electronic charge and its electronic chemical poten-
tial must be negative. The energies of frontier molecular orbitals
2
characterized by ꢀ ꢀ
> 0 and HBCP > 0 and they are mainly elec-
BCP
2
trostatic. The weak interactions are characterized by ꢀ ꢀ
> 0 and
BCP
H
BCP
> 0 and the distance between interacting atoms is greater than
the sum of van der Waal’s radii of these atoms.
Molecular graph of the dimer using AIM program at B3LYP/6-
3
1G(d,p) level is given in Supplementary Fig. 3. Geometrical as
well as topological parameters for bonds of interacting atoms in
dimer are given in (Supplementary Table) TS4. On the basis of these
parameters, O23· · ·H35, O62· · ·H65 are medium hydrogen bonds,
O12· · ·H82, O86· · ·H28 are weak hydrogen bonds and N10· · ·H42,
N64· · ·H59, O13· · ·H32, O87· · ·H79, C8· · ·H45, C75· · ·H71, C6· · ·N10,
C77· · ·N64, O12· · ·H83, O86· · ·H29 are weak interactions. The vari-
ous type of interactions visualized in molecular graph are classified
on the basis of geometrical, topological and energetic param-
eters. In this article, the Bader’s theory application is used to
estimate hydrogen bond energy (E). Espinosa proposed propor-
tionality between hydrogen bond energy (E) and potential energy
density (VBCP) at H· · ·O contact: E = (1/2)(VBCP) [56]. According
to AIM calculations, the binding energy of dimer is sum of the
energies of all intermolecular interactions and this is calculated
as −15.4539 kcal/mol. The intermolecular hydrogen bond energy
of dimer is sum of the energies of both heteronuclear inter-
molecular hydrogen bonds (N H· · ·O) and this is calculated as
(
εHOMO, εLUMO), energy band gap (εHOMO − εLUMO), electronegativ-
ity (ꢄ), chemical potential (ꢅ), global hardness (Á), global softness
S) and global electrophilicity index (ω) for reactants A, B and prod-
(
uct C are listed in (Supplementary Table) TS6. The calculated high
value of electrophilicity index (ω) for EDPHEDPC shows that the
title molecule behaves as a strong electrophile than reactants A
and B.
4.7.2. Local reactivity descriptors
Fukui functions (fk+, fk , fk ), local softnesses (sk+, sk−, sk0) and
−
0
+
−
0
local electrophilicity indices (ωk , ωk , ωk ) have been described
earlier in literature [62,63]. Using Hirshfeld population analyses
of neutral, cation and anion state of molecule, Fukui functions are
calculated at same calculation method B3LYP/6-31G(d,p) using Eqs.
(6)–(8)
−
12.5074 kcal/mol.
The ellipticity (ε) at BCP is a sensitive index to monitor the ␲-
character of bond. The ε is related to ꢂ1 and ꢂ , which correspond
to the eigen values of Hessian and defined as by a relationship:
2
+
f k = [q(N + 1) − q(N)], for nucleophilic attack
(6)
(7)
(8)
ε = (ꢂ /ꢂ ) − 1. In order to investigate the effect of ␲-electron delo-
1
2
−
f k = [q(N) − q(N − 1)], for electrophilic attack
calization in bonds associated with N and O atoms of N H· · ·O
heteronuclear inter and intramolecular hydrogen bonds, the anal-
ysis of the bond ellipticity is performed. In dimer, inter and
intramolecular hydrogen bonds are associated with the sixteen-
membered and six-membered pseudo ring respectively. These
f k0 = (1/2)[q(N + 1) + q(N − 1)], for radical attack
where N, N − 1, N + 1 are total electrons present in neutral, cation
and anion state of molecule respectively.

R.N. Singh et al. / Spectrochimica Acta Part A 92 (2012) 295–304
303
Local softnesses and electrophilicity indices are calculated using
the following equations ((9) and (10)).
show that the titled molecule might have medium non-linear opti-
cal (NLO) response.
sk = Sf k+
+
,
sk = Sf
−
−
,
sk0 = Sf k0
(9)
k
5
. Conclusions
ωk = ωf k+
+
,
ωk = ωf k−
−
,
ωk0 = ωf k0
(10)
The title compound EDPHEDPC is synthesized and characterized
where +, −, 0 signs show nucleophilic, electrophilic and radical
attack respectively.
by various spectroscopic and elemental analysis. The calculated
1
H NMR chemical shifts are in good agreement with the observed
Electrophilic reactivity descriptors (f +, s +, ωk+) and nucle-
k
k
chemical shifts. The 1H NMR signal of N11 H35 at high value of
chemical shifts 11.73 ppm confirms the presence of intramolecular
hydrogen bond N11 H35· · ·O23. The observed electronic absorp-
tion spectra have some blue shifts compared with the theoretical
data and molecular orbital coefficient analysis suggests that elec-
−
−
−
ophilic reactivity descriptors (fk , sk , ωk ) for selected atomic sites
of EDPHEDPC are listed in (Supplementary Table) TS7, using Hirsh-
feld population analyses. The maximum values of all the three local
electrophilic reactivity descriptors (fk , sk , ωk ) at C(7) indicate
that this site is more prone to nucleophilic attack. The calculated
local reactivity descriptors of synthesized molecule EDPHEDPC
favor the formation of new heterocyclic compounds such as azetidi-
nones, oxadiazolines and thiazolidinones by attack of nucleophilic
part of the dipolar reagent on the C(7) site and electrophilic part of
dipolar reagent on the N(10) site of C7 N10 bond.
+
+
+
*
tronic transitions are assigned to ␲ → ␲ . In the present study,
experimental and calculated vibrational wavenumber analysis con-
firms the existence of dimer by involvement of heteronuclear
association through pyrrolic (N H) and carbonyl (C O) oxygen of
ester. The calculated binding energies of dimer using both DFT
and AIM theories are −14.32 and −15.41 kcal/mol respectively.
AIM theory is more appropriate than DFT theory since this is also
applicable to calculate the intermolecular hydrogen bond energy
of dimer. The intermolecular hydrogen bond energy of dimer is
calculated to be −12.29 kcal/mol. The results of AIM ellipticity
confirm the existence of resonance assisted intra and intermolec-
ular hydrogen bonds in dimer. In addition, theoretical results from
reactivity descriptors show that C(7) is more reactive site for nucle-
ophilic attack. Therefore, title molecule may be used as precursor
for the syntheses of new heterocyclic compounds such as azetidi-
nones, oxadiazolines and thiazolidinones. The computed value of
4
.8. Dipole moment (ꢅ ), mean polarizability (˛ ), anisotropy of
polarizability (ꢁ˛) and first hyperpolarizability (ˇ0)
0
0
First hyperpolarizability is a third rank tensor that can be
described by a 3 × 3 × 3 matrix. The 27 components of the 3D-
matrix can be reduced to 10 components due to the Kleinmann
symmetry [62]. It can be given in the lower tetrahedral format. It is
obvious that the lower part of the 3 × 3 × 3 matrix is a tetrahedral.
The components of ˇ are defined as the coefficients in the Taylor
0
series expansion of the energy in the external electric field. When
the external electric field is weak and homogeneous this expansion
becomes:
first hyperpolarizability (ˇ ) shows that EDPHEDPC is an attractive
molecule in future for nonlinear optical (NLO) applications.
0
0
E = E − ꢅ F − (1/2)˛ F F − (1/6)ˇ F F F − · · ·
Acknowledgments
i
i
ij
i
j
ijk i j k
where E0 is the energy of the unperturbed molecules, F is the field
i
The authors are thankful to the Directors of IIT Kanpur and CDRI
Lucknow for providing spectral measurements of EDPHEDPC and
the CSIR New Delhi for financial supports.
at the origin and ꢅ , ˛ , ˇ are the components of dipole moment,
i
ij
ijk
polarizability, and first hyperpolarizability respectively. The total
dipole moment (ꢅ ), the mean polarizability (|˛ |), the anisotropy
0
0
of the polarizability (ꢁ˛) and the total first hyperpolarizability (ˇ )
0
Appendix A. Supplementary data
using x, y, z components are defined as [64]:
ꢅ = (ꢅ x + ꢅ y + ꢅ2z)1/2
2
2
(11)
(12)
(13)
(14)
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2012.02.086.
|
˛ | = (1/3)(˛xx + ˛yy + ˛zz)
˛ = 2− [(˛xx − ˛yy) + (˛yy − ˛zz) + (˛zz − ˛xx) ]
0
1/2
2
2
2 1/2
ꢁ
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