Synthesis, molecular structure and spectral analysis of ethyl 4-[(3,5-dinitrobenzoyl)-hydrazonomethyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate: A combined experimental and quantum chemical approach

Article abstract of DOI:10.1016/j.saa.2011.11.057

A new hydrazone, ethyl 4-[(3,5-dinitrobenzoyl)-hydrazonomethyl]-3,5- dimethyl-1H-pyrrole-2-carboxylate (PDNBAH) has been synthesized and characterized by FT-IR, ¹H NMR, UV-visible spectroscopy. All the quantum chemical calculations have been performed by density functional theory (DFT), using B3LYP functional and 6-31G(d,p) as basis set. The calculated and experimental wavenumber analyses confirm the existence of dimer of PDNBAH. The calculated binding energies of dimer using DFT and Bader's atoms in molecules (AIM) theory are -14.32 and -15.41 kcal/mol respectively. The intermolecular hydrogen bond energy of dimer due to the involvement of intermolecular hetero-nuclear double hydrogen bonds (NH?OC) through pyrrolic NH and CO of ester is also calculated to be equal to -12.29 kcal/mol using AIM calculation. The strength and the nature of hydrogen bonding and weak interactions in dimer have been analyzed by AIM theory in detail. The presence of resonance assisted hydrogen bonds (RAHB) has been confirmed by calculated ellipticity parameters using AIM calculation. The calculated thermodynamic parameters show that the reaction is non spontaneous at room temperature. The local reactivity descriptors show that C(13) is most reactive site for nucleophilic attack.

Full text of DOI:10.1016/j.saa.2011.11.057

Spectrochimica Acta Part A 88 (2012) 60–71
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, molecular structure and spectral analysis of ethyl 4-[(3,5-
dinitrobenzoyl)-hydrazonomethyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate: A
combined experimental and quantum chemical approach
R.N. Singh∗, Divya Verma, Amit Kumar, Vikas Baboo
Department of Chemistry, University of Lucknow, Lucknow 226007, U.P., India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 October 2011
Accepted 27 November 2011
A
new hydrazone, ethyl 4-[(3,5-dinitrobenzoyl)-hydrazonomethyl]-3,5-dimethyl-1H-pyrrole-2-
carboxylate (PDNBAH) has been synthesized and characterized by FT-IR, 1H NMR, UV–visible
spectroscopy. All the quantum chemical calculations have been performed by density functional
theory (DFT), using B3LYP functional and 6-31G(d,p) as basis set. The calculated and experimental
wavenumber analyses confirm the existence of dimer of PDNBAH. The calculated binding energies
of dimer using DFT and Bader’s atoms in molecules (AIM) theory are −14.32 and −15.41 kcal/mol
respectively. The intermolecular hydrogen bond energy of dimer due to the involvement of intermolec-
ular hetero-nuclear double hydrogen bonds (N H· · ·O C) through pyrrolic N H and C O of ester is
also calculated to be equal to −12.29 kcal/mol using AIM calculation. The strength and the nature of
hydrogen bonding and weak interactions in dimer have been analyzed by AIM theory in detail. The
presence of resonance assisted hydrogen bonds (RAHB) has been confirmed by calculated ellipticity
parameters using AIM calculation. The calculated thermodynamic parameters show that the reaction is
non spontaneous at room temperature. The local reactivity descriptors show that C(13) is most reactive
site for nucleophilic attack.
Keywords:
DFT
Vibrational spectra
1H NMR
Hydrogen-bonded dimer
AIM
Reactivity descriptor
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
2,4-dinitrophenylhydrazones of pyrrole-␣ꢀ-carboxaldehyde has
been used for the development of potential chemosensors [27]. In
Hydrazones are an important class of compounds due to their
various properties and applications. These are versatile starting
materials for the synthesis of a variety of N, O or S containing
class of compounds such as oxadiazolines, thiazolidinones, triazo-
lines, and various types of other organic compounds [1–7]. Due
addition, they have strong coordinating ability towards different
metal ions [28,29]. Aroyl hydrazones and their mode of chelation
with transition metal ions present in the living system had been of
significant interest in the past [30,31]. In particular, the interest in
PDNBAH is due to the above applications and the fact that the pyr-
role fragment is a constituent of many biological systems. In order
to obtain further information about pyrrole containing hydrazone,
PDNBAH is synthesized and characterized. In the present paper we
report the dimer structure of PDNBAH using quantum chemical
calculations and experimental FT-IR spectrum. Quantum chemi-
cal calculations have been performed to investigate the detailed
spectroscopic analyses, resonance assisted hydrogen bonding, and
chemical reactivity of the synthesized compound.
to the presence of
N N C 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 NH
N CH constitute an important class of compounds
for new drug development [10–14]. They are mainly used as antimi-
crobial, antitubercular [15–19] and antidiabetic agents [20]. The
chemical stability of hydrazones and their high melting points
have recently made them attractive as prospective new materials
for opto-electronic applications [21]. They have also been used as
potentially DNA damaging and mutagenic agents [22,23]. In partic-
ular, the nitro phenyl hydrazones exhibit a series of organic good
nonlinear optical (NLO) properties [24–26]. The anion receptor
1.1. General procedures
All the chemicals used were of analytical grade. The solvent
methanol was dried and distilled before use according to the stan-
dard procedure [32]. 3,5-Dinitrobenzhydrazide was synthesized
by reflux of the reaction mixture of ethyl 3,5-dinitrobenzoate
and hydrazine hydrate in methanol. Ethyl 4-acetyl-3,5-dimetyl-
1H-pyrrole-2-carboxylate was synthesized by an earlier reported
∗
Corresponding author. Tel.: +91 9451308205.
E-mail address: rnsvkchemistry.singh@gmail.com (R.N. Singh).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.11.057

R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
61
method [33]. The 1H NMR spectrum of PDNBAH was recorded
in DMSO-d6 on Bruker DRX-300 spectrometer using TMS as an
internal reference. The DART-mass spectrum was recorded on
JEOL-Acc TDF JMS-T100L C mass spectrometer. The FT-IR-spectrum
was recorded in KBr medium on a Bruker-spectrophotometer. The
UV–visible absorption spectrum of PDNBAH (1 × 10−5 M in DMSO)
was recorded on ELICO SL-164.
1.2. Synthesis of PDNABH
The solution of ethyl 4-acetyl-3,5-dimetyl-1H-pyrrole-2-
carboxylate (0.100 g, 0.4779 mmol) in 10 ml methanol was added
dropwise to a stirred solution of 3,5-dinitrobenzhydrazide (0.094 g,
0.4779 mmol) dissolved in 20 ml methanol. Two drops of polyphos-
phoric acid were added as a catalyst. Reaction mixture was refluxed
for 40 h. A yellow color precipitate appeared. The precipitate was
filtered off, washed with methanol and dried in air. Yield: 40.09%;
m.p. decomposed above 272 ◦C; 1H NMR (DMSO-d6): ı (ppm): ı
1.282 (3H, t, CH3 ester); ı 2.348 (3H, s, py-5-CH3); ı 2.308 (3H,
s, py-3-CH3); ı 2.50 (6H, s, DMSO-d6); ı 2.43 (3H, s, C(CH3) N);
ı 4.217 (2H, q, CH2 ester); ı 8.776 (1H, s, Ar-H); ı 8.86–8.92 (1H,
d, Ar-H); ı 9.095 (1H, s, Ar-H); ı 11.63 (1H, s, Py-NH), 11.49 (1H,
s, Ar-NH); DART-mass: observed m/z 418.24 [M++1]; calculated
417.12 amu; elemental analysis: observed C 51.88%, H 4.52%, N
16.72%, O 26.28% and calculated C 51.82%, H 4.59%, N 16.78%, O
26.84%.
2. Computational methods
All the calculations of the synthesized compound were carried
out with Gaussian 03 program package [34] to predict the molec-
ular structure, 1H NMR chemical shifts, vibrational wavenumbers
and energies of the optimized structure 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 is used for better description of polar
bonds of molecule [37,38]. It should be emphasized that ‘p’ polar-
ization functions on hydrogen atoms are used for reproducing the
out of plane vibrations involving hydrogen atoms. Convergence
criteria in which both the maximum force and displacement are
smaller than the cut-off values of 0.000450 and 0.001800 and r.m.s.
force and displacement are less than the cut-off values of 0.000300
and 0.001200 are used in the calculations. The time dependent
density function (TD-DFT) is carried out to find the electronic tran-
sitions. The optimized geometrical parameters are used in the
vibrational wavenumber calculation to characterize all stationary
points as minima and their harmonic vibrational wavenumbers are
positive. The vibrational wavenumbers in the harmonic approx-
imation are calculated using B3LYP/6-31G(d,p) and scaled down
using single scaling factor [39]. All molecular structures are visual-
ized using softwares Chemcraft [40] and GaussView [41]. Potential
energy distribution along internal coordinates is calculated by
Gar2ped software [42]. Internal coordinate system recommended
by Pulay et al. is used for the assignment of vibrational modes [43].
Fig. 1. (a) Optimized geometry of lower energy ground state conformer using
B3LYP/6-31G(d,p). (b) Optimized geometry of dimer of lower energy ground state
conformer using B3LYP/6-31G(d,p).
is shown in Fig. 1a, with atom numbering. The asymmetry of the
N1 C2 and N1 C5 bonds can be explained on the basis of electron
withdrawing nature of the ethoxycarbonyl group and conjugation
of the N1 C5 with C4 C3 C2 skeleton. This leads to the elon-
gation of N1 C2 bond. These effects are not only evident in the
quantum calculation but are also reflected in the crystal structures
of the ethyl-3,5-dimethyl-1H-pyrrole-2-carboxylate [44], methyl
4-p-tolyl-1H-pyrrole-2-carboxylate [45] and other 1H-pyrrole-2-
carboxylate [46]. The optimized geometry of dimer of the most
stable syn-conformer is shown in Fig. 1b, with atom number-
ing. In dimer, heteronuclear intermolecular hydrogen bonding
(N H· · ·O C) between pyrrolic (N H) and carbonyl (C O) oxygen
of ester forms double hydrogen bonds. In dimer both molecules
exist in s-cis form, with (N H) bond as proton donor and (C O)
bond as proton acceptor. According to the Etter terminology [47]
the cyclic ester dimer forms the ten membered ring denoted
as R22(10) or more extended sixteen membered ring R22(16).
The superscript designates the number of acceptor centers and
the subscript, the number of donors in the motif. In dimer, due
3. Results and discussion
3.1. Molecular geometry
The optimized geometrical parameters of the most stable syn-
conformer of monomer, calculated using DFT/B3LYP/6-31G(d,p)
method are listed in Table 1. The optimized geometry of monomer

62
R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
Table 1
˚
Selected optimized geometrical parameters of monomer using B3LYP/6-31G(d,p) [bond length (in A), bond angle (in degrees) and dihedral angle (in degrees)].
˚
Bond
Bond length in (A)
Bond angle
In degrees
Dihedral angle
In degrees
R(1,2)
R(1,5)
R(1,18)
R(2,3)
R(2,8)
R(3,4)
R(3,7)
R(4,5)
R(4,13)
R(5,6)
R(6,19)
R(6,20)
R(6,21)
R(7,22)
R(7,23)
R(7,24)
R(8,9)
R(8,10)
R(10,11)
R(11,12)
R(11,25)
R(11,26)
R(12,27)
R(12,28)
R(12,29)
R(13,14)
R(13,43)
R(14,15)
R(15,16)
R(15,30)
R(16,17)
R(16,31)
R(31,32)
R(31,33)
R(32,34)
R(32,35)
R(33,36)
R(33,37)
R(34,38)
R(34,47)
R(36,38)
R(36,40)
R(38,39)
R(40,41)
R(40,42)
R(43,44)
R(43,45)
R(43,46)
R(47,48)
R(47,49)
1.3827
1.3504
1.0107
1.3929
1.4582
1.435
1.5032
1.4099
1.466
A(2,1,5)
A(2,1,18)
A(5,1,18)
A(1,2,3)
A(1,2,8)
A(3,2,8)
A(2,3,4)
A(2,3,7)
A(4,3,7)
A(3,4,5)
A(3,4,13)
A(5,4,13)
A(1,5,4)
A(1,5,6)
A(4,5,6)
A(2,8,9)
111.2269
121.6006
127.1725
107.7417
115.9567
136.3006
106.3482
125.5509
128.0428
107.691
128.7335
123.5693
106.9872
121.53
131.4819
122.536
114.0652
123.3978
115.5107
107.4706
116.0461
120.7532
123.1455
118.346
119.3732
120.8499
119.4081
124.4356
114.6222
120.9385
123.9734
116.6376
119.3329
119.3321
119.3361
122.5593
118.6925
118.7473
122.6174
119.007
D(5,1,2,8)
D(2,1,5,6)
D(8,2,3,4)
D(1,2,8,10)
D(2,3,4,13)
D(4,3,7,22)
D(3,4,5,6)
D(3,4,13,14)
D(1,5,6,19)
D(2,8,10,11)
D(8,10,11,12)
D(10,11,12,27)
D(4,13,14,15)
D(4,13,43,44)
D(13,14,15,16)
D(14,15,16,31)
D(15,16,31,33)
D(16,31,32,34)
D(16,31,33,36)
D(31,32,34,47)
D(31,33,36,40)
D(32,34,38,39)
D(32,34,47,48)
D(33,36,38,39)
D(33,36,40,41)
179.4023
−179.6808
−179.7748
179.1328
179.6507
157.3014
179.6457
−153.3254
−133.8622
179.743
179.4736
−179.715
−178.2721
−112.8654
171.1018
176.0358
156.9178
−178.4435
178.9499
179.967
1.4934
1.093
1.0936
1.0946
1.0895
1.0938
1.0975
1.2236
1.3522
1.4471
1.5162
1.0942
1.0943
1.0943
1.0938
1.0937
1.2961
1.5159
1.3676
1.3768
1.0135
1.2195
1.5105
1.3982
1.4009
1.3936
1.0829
1.3894
1.0827
1.3885
1.4766
1.3913
1.4791
1.0812
1.2286
1.2275
1.0977
1.0872
1.0977
1.2274
1.2302
A(2,8,10)
A(9,8,10)
A(8,10,11)
A(10,11,12)
A(4,13,14)
A(4,13,43)
A(14,13,43)
A(13,14,15)
A(14,15,16)
A(14,15,30)
A(16,15,30)
A(15,16,17)
A(15,16,31)
A(17,16,31)
A(16,31,32)
A(16,31,33)
A(32,31,33)
A(31,32,34)
A(31,33,36)
A(32,34,38)
A(32,34,47)
A(38,34,47)
A(33,36,38)
A(33,36,40)
A(38,36,40)
A(34,38,36)
A(36,40,41)
A(36,40,42)
A(41,40,42)
A(45,43,46)
A(34,47,48)
A(34,47,49)
A(48,47,49)
179.2718
179.9203
−179.387
−179.6012
179.5633
118.3753
116.8055
117.246
117.343
125.4109
106.9344
117.4887
117.2744
125.2364
to intermolecular hydrogen bond formation both proton donor
(N H bond) and proton acceptor (C O bond) are elongated from
chemical shifts is shown in Fig. 2b. The correlation graph follows
the linear equation, y = 1.31629x − 1.45422, where ‘y’ is the 1H NMR
chemical shift and ‘x’ is the calculated 1H NMR chemical shift (ı
in ppm). The correlation value (R = 0.97982) shows that there is a
good agreement between the experimental and calculated chemi-
cal shifts.
˚
˚
˚
˚
1.01069 A to 1.02068 A and from 1.22357 A to 1.23204 A respec-
tively. The binding energy of the analyzed dimer is computed as
the difference between the calculated total energy of the dimer and
the energies of the two isolated monomers. The binding energy of
dimer is calculated to be −14.32 kcal/mol using DFT.
3.3. UV–visible spectroscopy
3.2. 1H NMR spectroscopy
The nature of the transitions observed in the UV–visible
spectrum of PDNBAH has been studied by the time-dependent
density functional theory (TD-DFT). The observed and calculated
electronic transitions of high oscillatory strength are given in
Table 3. Theoretical UV–visible spectrum of the compound is
shown in Fig. 3a. Frontier molecular orbitals (FMOs) i.e. the
highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) are shown in Fig. 3b.
The HOMO and LUMO are very popular quantum chemi-
cal parameters. They determine the molecular reactivity and
the ability of a molecule to absorb light. The HOMO is the
The geometry of the title compound, together with that of
tetramethylsilane (TMS) is fully optimized. 1H NMR chemical shifts
are calculated with GIAO approach using B3LYP method and 6-
31G(d,p) basis set [48]. Chemical shift of any ‘X’ proton (CSX)
is equal to the difference between isotropic magnetic shield-
ing (IMS) of TMS and ‘X’ proton. It is defined by the equation:
CSX = IMSTMS − IMSX. The experimental and calculated values of 1
H
NMR chemical shifts of the title compound are given in Table 2.
The experimental 1H NMR spectrum of PDNBAH is shown in Fig,
2a. The correlation graph between the experimental and calculated

R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
63
Table 2
3.4. Vibrational assignments
Experimental and calculated GIAO 1H NMR chemical shifts using DFT/B3LYP/6-
31G(d,p).
The observed and calculated (dimer) vibrational wavenumbers
with their assignment using potential energy distribution (PED) are
given in Table 4a. The calculated and the experimental FT-IR spectra
of PDNBAH in the region 4000–400 cm−1 are shown graphically in
Fig. 4. The total number of atoms in monomer and dimer are 49 and
98 respectively, which gives 141 and 288 (3n − 6) vibrational modes
for monomer and dimer respectively. Geometrical parameters for
hydrogen bonds in dimer are given in Table 4b. The calculated vibra-
tional wavenumbers are higher than their experimental values for
the majority of the normal modes. Two factors may be responsi-
ble for the discrepancies between the experimental and computed
wavenumbers of this compound. The first is caused by the envi-
ronment and the second is due to the fact that the experimental
values are anharmonic wavenumbers while the calculated values
are harmonic ones. Therefore, calculated wavenumbers are scaled
usingscalingfactorto discardtheanharmonicitypresentinrealsys-
tem. The vibrational wavenumbers calculated at B3LYP/6-31G(d,p)
level are scaled using single scaling factor (0.9679) [39]. The scaled
vibrational wavenumbers with their potential energy distribution
(PED) help in the assignment of vibrational modes obtained from
experimental FT-IR spectrum. GaussView program is also used to
assign the calculated harmonic vibrational wavenumbers. The cal-
culated wavenumbers of dimer are in close agreement with the
experimental wavenumbers, whereas in the monomer they differ.
The calculated vibrational wavenumbers of monomer with their
assignment using Gar2ped are given in Supplementary TS1.
Atom no.
ıexp.
ıcalc.
18 H
19 H
20 H
21 H
22 H
23 H
24 H
25 H
26 H
27 H
28 H
29 H
30 H
35 H
37 H
39 H
44 H
45 H
46 H
11.632
8.6331
2.4981
2.751
2.348
2.1216
3.0327
2.1256
2.3124
4.2952
4.2544
1.2424
1.4776
1.4825
9.0958
9.057
9.3801
9.4149
2.2142
2.4708
2.0617
2.308
4.217
1.271–1.293
11.491
8.776
8.86–8.92
9.095
2.143
orbital that could act as an electron donor, since it is the
outermost (higher energy) orbital containing electrons. The LUMO
is the orbital that could act as an electron acceptor, since it is the
innermost (lowest energy) orbital that has room to accept elec-
trons. The energies of HOMO and LUMO and their neighboring
orbitals are negative, which indicates that PDNBAH molecule is
stable [49]. The HOMO − LUMO energy gap is an important stabil-
ity index. The HOMO − LUMO energy gap of PDNBAH calculated
at B3LYP/6-31G(d,p) level reflects the chemical stability of the
molecule.
3.4.1. N H vibrations
In the FT-IR spectrum of PDNBAH, the N H stretch of pyr-
role (ꢁNH) is observed at 3265 cm−1, whereas it is calculated as
3360 cm−1 in dimer and 3525 cm−1 in monomer [50]. The observed
wavenumber is in agreement with the calculated wavenumber
of dimer. The observed value of ꢁNH correlates with the earlier
reported strong absorption at 3358 cm−1 for the hydrogen bonded
pyrrole-2-carboxylic acid recorded in KBr pellet, but it deviates
from the reported free ꢁNH band observed at higher wavenum-
ber 3465 cm−1, recorded in CCl4 solution [51]. Therefore, solid
state spectrum of PDNBAH, attributed to the vibration of hydro-
HOMO energy = −5.8197 eV;
LUMO energy = −3.2256 eV;
HOMO − LUMO energy gap = −2.5940 eV.
gen bonded N H group and the observed wagging at 622 cm−1
,
TD-DFT/B3LYP/6-31G(d,p) predicts two intense electronic tran-
sitions at ꢀmax = 352.12 nm, f = 0.4382 and ꢀmax = 252.73 nm,
f = 0.3908. These are in agreement with the experimental elec-
tronic transitions at ꢀmax = 328, 225 nm respectively. The calculated
intense electronic transition at ꢀmax = 234.02 nm, f = 0.3798 does
not appear in the experimental spectrum. The TD-DFT calculation
shows that the experimental longest wavelength band at 328 nm
and another experimental band at 225 nm originate due to the
H → L + 2 and H − 8 → L + 1 transition respectively. On the basis of
the calculated result, both observed electronic excitations show
␲ → ␲* transitions. The calculated ꢀmax values are in good agree-
ment with the experimental values.
confirms the involvement of pyrrole N H group in intermolecu-
lar attraction and correlates with earlier reported wagging mode
at 602 cm−1 for pyrrole N H in dimer of syn-pyrrole-2-carboxylic
acid [51]. The N H deformation of pyrrole is observed at 1483 cm−1
,
whereas it is calculated as 1547 cm−1. The hydrazide N H stretch
observed at 3423 cm−1 corresponds to the calculated wavenumber
at 3447 cm−1 in dimer and 3446 cm−1 in monomer.
3.4.2. C H vibrations
Four methyl groups are present in the molecule. Two of them
are directly attached to the ring, the third is connected to the CH2 of
Table 3
Comparison between experimental and calculated electronic transition using TD-DFT/B3LYP/6-31G(d,p): (E in eV), oscillatory strength (f), ꢀmax (in nm).
Excited
state no.
Electronic
transitions
E (eV)
Oscillatory
strength (f)
Calculated
(ꢀmax
Observed
% contribution of
probable transition
Assignment
)
(ꢀmax
)
5
19
23
109 → 112
109 → 113
101 → 110
109 → 114
101 → 111
104 → 112
105 → 112
108 → 113
108 → 114
3.5211
4.4937
4.8175
0.4382
0.4171
0.1212
352.12
275.9
257.36
328
46
39
10
25
30
14
10
11
41
␲ → ␲*
26
31
4.9058
5.1254
0.3908
0.1232
252.73
241.9
225
␲ → ␲*
33
5.2981
0.3798
234.02

64
R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
Table 4a
Experimental and calculated vibrational wavenumbers of dimer using B3LYP/6-31G(d,p) and their assignments [harmonic wavenumber (cm−1), IRint (K mmol−1)].
S.N.
Wavenumber (cm−1
)
IRint
Vibrational assignments (PED in %)
Unscaled
400.38
Scaled
Exp.
1
387.528
19.41
(ꢂ-H21C51)(15) (ω-N1H18)(14) (ꢂ-C58C59)(12)-(ꢂ-C5C6)(11) ω(C6C5)(10)
(ꢂ-H18O60)(5)
2
3
426.2
454.77
412.519
440.172
22.47
40.77
(ꢂ-H21C51)(51)-(ꢃ-Me)(24)
(ω-N1H18)(27) (ꢃ-Me)(12)-(ꢂ-C58C59)(10) ω(C6C5)(9) (ω-N61H64)(7)
ꢂꢀ(ring)(6)-(ꢂ-C5C6)(5)
4
5
6
7
474.16
478.93
481.26
531.14
458.939
463.556
465.812
514.09
3.27
2.88
5.74
6.44
(ꢂ-H21C51)(44) (ꢂ-H21C52)(39)-(ꢂ-C5C6)(5)
(ꢂ-H21C51)(44) (ꢂ-H21C52)(38)
(ꢂ-H21C52)(51) (ꢂ-H21C51)(21)
(ꢃ-N40O41O42)(9)
(ꢂ-H21C52)(9)-(ω-N1H18)(9)(ꢃ-N47O48O49)(7)-(ısc-N93O97O98)(7) (ꢃ-Me)(6)
(ısc-N92O96O95)(5)
8
9
542.88
555.23
525.454
537.407
14.67
9.05
(ꢂ-H21C52)(43) (ꢂ-H21C51)(21)-(ꢂ-C5C6)(8) (ꢃ-Me)(6)-(ꢃꢀ-Me)(5)
(ꢂ-H21C51)(22) (ω-N1H18)(18)-(ꢂ-C5C6)(17) (ꢂ-H21C52)(10) ꢂꢀ(ring)(9)
ω(C6C5)(6)-(ω-N61H64)(5)
10
11
12
13
14
638.27
648.97
665.34
695.26
715.99
617.782
628.138
643.983
672.942
693.007
622
7.95
26.75
23.16
30.73
4.33
ꢂꢀ(ring)(35) (ω-N1H18)(26)-(ω-N61H64)(7)
(ꢂ-H21C52)(36) (ꢂ-H21C51)(21)-(ꢂ-C5C6)(7) (ꢃ-Me)(7)
(ꢂ-H21C52)(32) (ꢂ-H21C51)(21)-(ꢂ-C5C6)(12) (ꢃ-Me)(7)
(ꢂ-H21C51)(32) (ω-N1H18)(14) (ꢂ-H21C52)(14) ꢂꢀ(ring)(10)-(ꢂ-C5C6)(7)
(ꢂ-C5C6)(30)-(ω-N1H18)(18)-(ꢂ-H21C51)(12)-ꢂꢀ(ring)(10)-ꢂ(ring)(6)-ω(C6C5)(5)
(ω-N61H64)(5)
15
16
729.72
742.41
706.296
718.579
84.13
96.56
(ꢂ-C5C6)(30)-(ω-N1H18)(12)-(ꢂ-H21C51)(11)-ꢂꢀ(ring)(11)-ꢂ(ring)(6)-ω(C6C5)(5)
(ω-N1H18)(33) ꢂꢀ(ring)(10)-(ω-N61H64)(9)
(ꢂ-H21C51)(8)-(ꢂ-C58O55)(7)-(ꢂ-H18O60)(5)
17
18
749.17
755.96
725.122
731.694
12.69
98.95
(ꢂ-C58O55)(21) (ω-N1H18)(16)-(ꢂ-H18O60)(15) (ω-C58C59)(11) ꢂꢀ(ring)(10)
(ω-C59C58)(6)
(ꢂ-H21C51)(30) (ꢂ-H21C52)(14) (ꢂ-C58O55)(12)-(ω-N1H18)(6)
(ω-C58C59)(6)-(ꢂ-C5C6)(6)-(ꢃ-Me)(6)
722.41
19
20
764.92
767.02
740.366
742.399
6.25
2.09
(ꢂ-C5C6)(20)-(ꢂ-H21C51)(17) (ꢂ-H18O60)(8)-(ω-N1H18)(7)-(ꢂ-H21C52)(6)-ꢂ(ring)(5)
(ω-N1H18)(19)-ı(C52C58O55)(13) ı(O60C58O55)(10) (ꢂ-H21C51)(9) (ω-N61H64)(6)
ꢂꢀ(ring)(5)-(ꢂ-C5C6)(5)
21
774.12
749.271
36.68
(ꢂ-H18O60)(18)-(ω-N1H18)(17)-ı(C52C58O55)(13) ı(O60C58O55)(13)-(ꢂ-O9H64)(5)
(ω-N61H64)(5)
22
23
24
25
26
831.19
850.72
871.04
905.77
934.13
804.509
823.412
843.08
876.695
904.144
778.75
114
6.24
9.42
19.42
48.47
(ω-N1H18)(41)-(ꢂ-H18O60)(37) (ω-N61H64)(11)-(ꢂ-O9H64)(10)
(ꢃ-Me)(37)-(ꢂ-H21C51)(30)-ı(C52C58O55)(8) (ω-CH2)(7)
(ꢃ-Me)(47)-(ꢂ-H21C51)(29) (ω-CH2)(10)
(ꢂ-H21C51)(43)-(ꢃ-Me)(35)-(ω-CH2)(10) (ꢂ-H21C52)(6)
(ꢂ-H21C51)(18)-␯(C34–N47)(10) (ꢂ-H21C52)(9) ꢁ(C16–N40)(8)-(ꢃ-N47O48O49)(6)
ıꢀas(ring)(5) (ısc-N40O41O42)(5) ꢁ(C87–N92)(5)
27
946.09
915.721
9.04
(ω-C32H35)(23) (ω-C85H88)(18) (ꢂ-H21C52)(10)-puck(ring)(6)
(ꢂ-H21C51)(6)-puck(ring)(5)
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
959.94
963.42
983.57
990.64
1049
929.126
932.494
951.997
958.84
1015.36
1023.1
1026.67
1030.04
1051.35
1057.68
1074.53
1093.3
1102.63
1110.21
1146.26
1153.94
1200.04
1201.58
1216.59
18.25
2.09
(ω-C38H39)(42) (ω-C91H94)(32)-puck(ring)(7)-puck(ring)(5)
(ꢂ-H21C52)(37) (ꢂ-H21C51)(29) (ꢃ-Me)(5)
927.58
22.56
146.9
57.94
28.18
3.01
(ω-C86H90)(29) (ω-C33H37)(28)-(ꢂ-H21C51)(11)-(ꢂ-H21C52)(7)
(ꢂ-H21C51)(46) (ꢂ-H21C52)(34)-(ꢃꢀ-Me)(6)
(ꢂ-H21C51)(36)-(ꢃ-Me)(29)-(ꢂ-C51C52)(13) (ꢂ-H21C52)(5)-(ω-CH2)(5)
(ꢂ-C5C6)(28)-(ꢂ-H21C52)(24) (ꢃꢀ-Me)(22)-(ꢂ-H21C51)(16) (ıas-Me)(4)
(ꢂ-H21C51)(51) (ꢂ-H21C52)(17) (ꢂ-C5C6)(15)-(ıꢀas-Me)(4) (ꢃꢀ-Me)(4)
(ꢂ-H21C51)(44) (ꢂ-C5C6)(26) (ꢂ-H21C52)(12) (ꢃꢀ-Me)(7)-(ıꢀas-Me)(5)
(ꢂ-H21C52)(29) (ꢂ-H21C51)(25)-(ꢂ-C5C6)(22)-(ꢃꢀ-Me)(16)-(ıas-Me)(2)
ı(C34H39C38)(15)-ı(C87H94C91)(14)-(ꢃ-Me)(9)-(ꢂ-C51C52)(8) (ꢂ-H21C51)(4)
(ꢂ-H21C51)(28)-(ꢂ-C5C6)(17)-(ꢃ-Me)(16)-(ꢂ-C51C52)(13)-(ꢃꢀ-Me)(9) (ꢂ-H21C52)(7)
(ꢃ-Me)(41) (ꢂ-C51C52)(30)-(ꢂ-H21C51)(11) (ıꢀas-Me)(6) (ꢂ-H21C52)(5)
(ꢃ-Me)(40)-(ꢂ-H21C51)(29) (ꢂ-C51C52)(23) (ıꢀas-Me)(5)
(ꢃ-Me)(41)-(ꢂ-H21C51)(33) (ꢂ-C51C52)(16) (ıꢀas-Me)(5)
(ꢂ-C51C52)(32)-(ꢂ-C58O55)(24)-(ꢂ-H21C52)(14) (ꢃꢀ-Me)(13)
(ꢂ-H21C51)(30) (ꢂ-H21C52)(28)-(ꢂ-C5C6)(15)-(ꢃꢀ-Me)(11)
(ω-CH2)(48)-(ꢂ-C51C52)(20)-(ꢂ-H21C52)(18)
1057
1021.65
1060.7
1064.2
1086.2
1092.8
1110.2
1129.6
1139.2
1147
1184.3
1192.2
1239.8
1241.4
1256.9
8.08
12.75
183.66
3.98
214.61
54.23
230.71
6.22
406.11
587.43
9.43
1070.97
1102.03
1133.7
1183.79
(ω-CH2)(53)-(ꢂ-C51C52)(24) (ꢂ-H21C51)(7)
16.62
ı(C31H37C33)(14) ı(C89H90C86)(14)-ı(C31H35C32)(12)
ı(C84H88C85)(12)-ı(C34H39C38)(11) ı(C87H94C91)(11)
(ꢂ-H21C51)(22) (ꢂ-H21C52)(14)-ꢁ(C16–C31)(7) ꢁ(C81–C84)(7)
(ꢂ-C51C52)(46)-(t-CH2)(20)-(ꢂ-H21C52)(15) (ꢂ-C58O55)(9)-(ꢃꢀ-Me)(5)
(ꢂ-H21C51)(48) (ω-CH2)(22) (ꢂ-H21C52)(16)
(ω-CH2)(48)-(ꢂ-C51C52)(14) (ꢂ-C5C6)(12)-(ꢂ-H21C52)(9) (ıas-Me)(7)
(ω-CH2)(50)-(ꢂ-C5C6)(15)-(ꢂ-C51C52)(14)-(ıas-Me)(8)
ꢁ(C84–C85)(8)-ꢁ(C84–C86) 8)-ꢁ(C31–C32)(8) ꢁ(C31–C33)(8) (ꢂ-C5C6)(8)
ꢁ(C87–C91)(6)-ꢁ(C34–C38)(5)-ꢁ(C89–C91)(5)-(ꢂ-H21C52)(5) ꢁ(C36–C38)(5)
(ω-CH2)(55)-(ꢂ-C5C6)(11)-(ꢂ-C51C52)(10)-(ıas-Me)(10)-(ꢂ-C58O55)(5)
(ω-CH2)(41)-(ꢂ-C51C52)(8)-(ꢂ-C5C6)(5)
47
48
49
50
51
52
1276.5
1296.7
1303.5
1324.7
1326.7
1384.2
1235.49
1255.08
1261.61
1282.21
1284.15
1339.77
1212.74
400.53
1.3
154.18
913.8
5.98
1277.49
1306.9
33.13
53
54
55
56
57
58
59
1393.4
1394.3
1401.1
1404.2
1412.5
1430
1348.64
1349.53
1356.12
1359.08
1367.18
1384.11
1385.29
3.96
693.17
4.27
427.64
18.97
62.62
12.79
(ω-CH2)(48)-(ꢂ-H21C52)(21)-(ꢂ-H21C51)(8)-(ꢂ-C51C52)(8)-(ꢂ-C58O55)(5)
(ꢂ-H21C52)(18)-(ω-CH2)(15) (ꢂ-H21C51)(13)-ꢁ(N93–O98)(4) ꢁ(N40–O42)(4)
(ω-CH2)(61)-(ꢂ-C58O55)(8) (ıs-Me)(8)-(ꢂ-C51C52)(6)-(ıs-Me)(5)
(ꢂ-H21C52)(65) (ıs-Me)(16)
1343.91
1431.2
(ꢂ-H21C52)(54) (ꢂ-H21C51)(36)

R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
65
Table 4a (Continued)
S.N.
Wavenumber (cm−1
)
IRint
Vibrational assignments (PED in %)
Unscaled
Scaled
Exp.
60
61
62
62
64
65
66
67
68
69
70
71
72
73
74
1438.1
1457
1391.89
1410.27
1421.33
1434.51
1437.62
1442.43
1446.76
1449.17
1452.34
1461.55
1465.52
1468.13
1477.24
1484.06
1509.47
23.91
(ꢂ-H21C51)(41) (ω-CH2)(25)-(ꢂ-C51C52)(10)-(ıs-Me)(7)-(ıꢀas-Me)(5)
(ıas-Me)(38) (ꢂ-C5C6)(26) (ω-CH2)(6)
(ıas-Me)(31) (ꢂ-C5C6)(27) (ꢂ-H21C51)(21) (ω-CH2)(8)
(ıas-Me)(40) (ꢂ-C5C6)(37) (ꢂ-H21C52)(10) (ꢂ-H21C51)(5)
(ꢂ-H21C51)(46)-(ıꢀas-Me)(35) (ꢂ-H21C52)(9)-(ıas-Me)(7)
(ꢂ-H21C51)(52)-(ıꢀas-Me)(26) (ꢂ-H21C52)(19)
3.12
427.76
213.24
38.85
20.99
41.01
40.97
16.64
50.39
3.29
1468.5
1482.1
1485.3
1490.3
1494.7
1497.2
1500.5
1510
1514.1
1516.8
1526.2
1533.3
1559.5
(ꢂ-H21C51)(28) (ꢂ-H21C52)(23) (ꢂ-C5C6)(21) (ıas-Me)(21)
(ꢂ-H21C51)(49) (ꢂ-H21C52)(18)-(ıꢀas-Me)(13) (ıꢀas-Me)(6) (ꢂ-C5C6)(5)
(ıꢀas-Me)(32)-(ıas-Me)(30) (ꢂ-H21C51)(22) (ꢂ-C51C52)(12)
(ıꢀas-Me)(26) (ꢂ-C51C52)(25)-(ꢂ-H21C51)(16)-(ıas-Me)(10)-(ꢂ-C5C6)(6)
(ıꢀas-Me)(44) (ꢂ-C51C52)(32)-(ꢂ-H21C51)(6) (ıas-Me)(5)
(ıꢀas-Me)(57) (ꢂ-C51C52)(23) (ꢂ-H21C52)(5)
116.2
41.4
5.78
(ıas-Me)(27)-(ıꢀas-Me)(17) (ꢂ-H21C51)(12) (ꢂ-H21C52)(12) (ꢂ-C5C6)(9)-(ꢃꢀ-Me)(7)
(ıꢀas-Me)(34)-(ꢂ-C51C52)(15) (ꢂ-C58O55)(15) (ıSC-CH2)(8)-(ꢂ-H21C51)(5)-(ꢃ-Me)(5)
(ꢂ-H21C52)(25) (ıas-Me)(24) (ꢂ-H21C51)(11)-(ꢃꢀ-Me)(9) (ꢂ-C5C6)(7)
(ꢂ-C51C52)(7)-(ω-CH2)(5)
70.42
75
76
77
1565.5
1566.8
1598.4
1515.24
1516.49
1547.06
1434.52
1483.90
1079.58
35.84
355.88
(ꢂ-H21C52)(25)-(ꢃꢀ-Me)(23) (ꢂ-H21C51)(17) (ıas-Me)(14)
(ꢃꢀ-Me)(23)-(ꢂ-H21C51)(22)-(ꢂ-H21C52)(20)-(ıas-Me)(14)
(ω-CH2)(18)-(ꢂ-H21C52)(12) ı(C2H18N1)(10) (ꢂ-C5C6)(8)-(ꢂ-C51C52)(8)
(ꢃꢀ-Me)(6)-(ıꢀas-Me)(5) ꢁ(N1 C5)(5)
78
79
1605.8
1624
1554.26
1571.87
7.47
53.22
(ω-CH2)(23)-(ꢂ-C51C52)(15)-ı(C2H18N1)(11)-(ꢂ-C5C6)(8)-ꢁ(N1 C5)(5)
ꢁ(C87 C91) 9)-ꢁ(C34 C38)(8)-ꢁ(C89 C91) 7) ꢁ(C36 C38)(7)
ꢁ(C84 C86)(6)-ꢁ(C84 C85)(5)-ꢁ(C31 C33)(5) ꢁ(C31 C32)(5)
ꢁ(N47 O48)(6)-ꢁ(N92 O95)(6)
ꢁ(N40 O41)(6)-ꢁ(N93 O97)(6)-ꢁ(N40 O42)(5)ꢁ(N93 O98)(5)-ꢁ(C33 C36)(5)
ꢁ(C86 C89)(5)-ꢁ(N47 O49)(5)
(ꢂ-H21C52)(20) (ꢂ-H21C51)(18) (ꢂ-C5C6)(12) (ıas-Me)(9)-ꢁ(C68N75)(8)
ꢁ(C13 N14)(8)
ꢁ(N93 O97) 8)-ꢁ(N93 O98)(8)-ꢁ(N40 O41)(8)–(7) ꢁ(N40 O42)(7) ꢁ(N47 O48)(7)
ꢁ(N92 O96)(6)-ꢁ(N47 O49)(6)
80
1631.9
1579.49
1537.91
1603.29
364.38
81
82
83
1656.8
1662.3
1688.1
1603.63
1608.89
1633.9
37.44
129.72
278.27
ꢁ(C33 C36)(6)-ꢁ(N40 O42)(6)-ꢁ(C86 H89) 6) ꢁ(N93 O98)(6)
ꢁ(C32 C34)(5)-ꢁ(C85 C87)(5) ꢁ(N40 O41)(5)
84
85
1721.3
1724.2
1666.08
1668.8
4.4
2105.14
(ꢂ-H21C52)(27) (ꢂ-H21C51)(14) ı(C52C58O55)(11)-(ω-CH2)(10) (ꢂ-C51C52)(8)
(ω-CH2)(20)-ı(C52C58O55)(18)-(ꢂ-C51C52)(13)-(ꢂ-H21C52)(12)-ꢁ(C58 O60)(7)
ı(O60C58O55)(6)-(ꢃ-Me)(5)
1675.53
86
87
88
89
1785.3
3027.9
3036.6
3057.3
1727.94
2930.69
2939.15
2959.16
477.28
18.46
53.95
32.14
ꢁ(C16 O17)(31)-ꢁ(C81 O83)(30) (ıas-Me)(9)
ꢁ(C43 H46)(31) ꢁ(C43 H44)(27)-ꢁ(C76 H80)(19)-ꢁ(C76 H79)(17)
ꢁ(C7 H24)(41)-ꢁ(C66 H71)(40) ꢁ(C7 H23)(7)-ꢁ(C66 H70)(6)
ꢁ(C51 H50)(14)-ꢁ(C12 H27)(14) ꢁ(C51 H53)(13)
ꢁ(C51 H54)(13)-ꢁ(C12 H28)(13)-ꢁ(C12 H29)(13)(ꢂ-H21C51)(11)-(ıs-Me)(6)
(ꢂ-H21C52)(26) ꢁ(C6 H21)(18)-ꢁ(C67 H72)(13)
ꢁ(C6 H19)(11)-ꢁ(C67 H74)(9)-ꢁ(C67 H73)(9) ꢁ(C6 H20)(7)
(ꢂ-C51C52)(29) (ꢃ-Me)(15)-ꢁ(C11 H26)(11) ꢁ(C52 H57)(10)
ꢁ(C52 H56)(9)-ꢁ(C11 H25)(9)-(ꢂ-C58O55)(9)
90
91
3061.8
3065.7
2963.47
2967.27
16.6
2920.93
52.68
92
93
3078.5
3107.4
2979.69
3007.66
11.87
9.4
ꢁ(C76 H79)(51)-ꢁ(C76 H80)(46)
(ꢂ-C58O55)(20)-(ꢃꢀMe)(11)
(ꢂ-H21C52)(9)-(ꢂ-C58O55)(9)-ꢁ(C11 H26)(9)ꢁ(C11 H25)(9)
ꢁ(C52 H56)(7)-ꢁ(C52 H57)(6)-(ꢂ-C51C52)(5)
94
95
96
97
3108.6
3122.5
3133
3008.82
3022.22
3032.44
3039.2
29.16
6.62
46.68
63.18
ꢁ(C7 H23)(47) ꢁ(C66 H70)(24)-ꢁ(C7 H24)(12)-ꢁ(C66 H71)(6)ꢁ(C7 H22)(6)
(ꢂ-H21C51)(43)-(ıꢀas-Me)(17) (ꢂ-C5C6)(16) (ꢂ-H21C52)(12)
(ꢂ-H21C51)(26)-(ꢂ-C51C52)(25)-(ıꢀas-Me)(17)-(ꢃ-Me)(15)
(ꢂ-C51C52)(18)-(ıas-Me)(14)
3140
2975.08
3097.16
(ıꢀas-Me)(12)-ꢁ(C12 H29)(9)-ꢁ(C51 H54)(8)ꢁ(C12 H28)(8)
ꢁ(C51 H53)(7)-(ꢃꢀ-Me)(5)
98
99
3152.9
3166.4
3186.4
3240
3254.6
3271.6
3466.2
3471.8
3561.4
3561.4
3051.72
3064.73
3084.11
3135.98
3150.11
3166.53
3354.89
3360.36
3447.09
3447.1
6.9
11.61
5.71
(ꢂ-C5C6)(49) ꢁ(C6 H21)(14) (ꢃꢀ-Me)(14)(ıas-Me)(13)-(ꢂ-H21C51)(5)
ꢁ(C66 H69)(76)-ꢁ(C66 H70)(12)-ꢁ(C7 H22)(9)
ꢁ(C43 H45)(94)
ꢁ(C85 H88)(54)-ꢁ(C32 H35)(45)
ꢁ(C33 H37)(52)-ꢁ(C86 H90)(48)
100
101
102
103
104
105
106
107
5.44
28.94
72.11
5.08
2699.87
42.58
10.4
ꢁ(C91 H94)(58)-ꢁ(C38 H39)(42)
ꢁ(N1 H18)(47) ꢁ(N61 H64)(38)-(ꢂ-H18O60)(10)
ꢁ(N1 H18)(47)-ꢁ(N61 H64)(38)-(ꢂ-H18O60)(10)
ꢁ(N77 H82)(65)-ꢁ(N15 H30)(34)
3265.86
3423.73
ꢁ(N15 H30)(65) ꢁ(N77 H82)(34)
Table 4b
˚
Geometrical parameters for hydrogen bonds in dimer [bond length (in A) and bond angle (in degrees)].
˚
˚
˚
N
H· · ·O
N
H (A)
H· · ·O (A)
N
O (A)
N
H· · ·O (degrees)
N1 H18· · ·O60
N61 H64· · ·O9
1.02068
1.02068
1.90313
1.90311
2.88574
2.88572
160.57201
160.57407

66
R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
Fig. 2. (a) Experimental 1H NMR spectrum of DNBAH. (b) Correlation graph between experimental and calculated GIAO 1H NMR chemical shifts using DFT/B3LYP/6-31G(d,p).
ester and the fourth is attached to the carbon of the C N bond. The
H stretching vibration in benzene ring observed at 3097 cm−1 is
calculated to be equal to 3166 cm−1. The C
C deformations in
3.4.3. C C vibrations
C
The C C stretches in benzene ring calculated at 1579 cm−1
correspond to the observed wavenumber at 1537 cm−1 in FT-IR
spectrum. The C16 C31 stretching vibrational mode calculated as
1235 cm−−11 corresponds to the vibrational wavenumber observed at
1212 cm . The wagging vibrational mode of C58 C59 is observed
H
benzene ring observed at 1070 cm−1 are calculated to be equal to
1057 cm−1 in dimer. The C H wagging in benzene ring is observed
at 927 cm−1, whereas it is calculated to be equal to 951 cm−1. The
stretching vibration of methyl group of ester observed at 2975 cm−1
is in agreement with the calculated wavenumber at 3039 cm−1. The
at 722 cm−1, whereas it is calculated as 731 cm−1
.
stretching vibration of CH2 group of ester is observed at 2920 cm−1
whereas it is calculated as 2967 cm−1 and the wagging vibration
mode of CH2 is observed at 1277 and it is calculated as 1282 cm−1
,
3.4.4. C O vibrations
The stretching vibrational mode of carbonyl group (ꢁC O) of
ester, at the observed wavenumber 1675 cm−1, corresponds to the
calculated wavenumber at 1668 cm−1 in dimer, whereas it is larger
than the calculated wavenumber at 1759 cm−1 for monomer. The
.
Rocking vibrational modes of different methyl groups are observed
at 1434, 1133 and 1102 cm−1 while the calculated values are 1515,
1153 and 1102 cm−1 respectively.
ꢁC
absorption band at 1675 cm−1 in the observed spectrum of
O

R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
67
Fig. 3. (a) Theoretical UV-spectrum of DNBAH. (b) HOMO–LUMO molecular orbital plots of DNBAH.
vibration is observed at 1537 cm−1, whereas it is calculated to
be equal to 1579 cm−1. Symmetric N O stretching vibration is
PDNBAH agrees well with the calculated wavenumber of dimer
at 1668 cm−1 but deviates from the calculated wavenumber of
monomer at 1759 cm−1. The ꢁC
absorption band at 1675 cm−1
observed at 1343 cm−1, whereas it is calculated as 1359 cm−1
.
O
in the observed spectrum of PDNBAH closely correlates with
the earlier reported wavenumber at 1665 cm−1 for dimer of
syn-pyrrole-2-carboxylic acid [51]. Therefore, stretching mode of
carbonyl group in PDNBAH confirms the involvement of C O group
in intermolecular attraction. The stretching vibrational mode of
carbonyl group (ꢁC O) in hydrazide part of molecule is calculated
to be equal to 1727 cm−1 in dimer but has not been observed
experimentally.
These wavenumbers are in close agreement with the earlier
reported wavenumbers for asymmetric and symmetric vibration
at 1600 cm−1 and 1319 cm−1 respectively [52].
3.4.6. C N vibrations
The C N stretching vibration is calculated as 1603 cm−1 which
is exactly the same as that observed in experimental FT-IR spec-
trum. The observed band at 1603 cm−1 correlates with the earlier
reported values 1570 cm−1 [35] and 1655 cm−1 [36].
3.4.5. N O vibrations
3.5. AIM calculation
The molecule under investigation possesses two nitro groups.
In aromatic nitro compounds symmetric and asymmetric stretch-
ing bands of N O occur at slightly lower wavenumber than in
nitro alkanes due to conjugation with the phenyl ring. Asymmetric
stretching vibrations are always observed at higher wavenumber
than symmetric stretching vibrations. Asymmetric N O stretching
3.5.1. ꢄ-Delocalization effect in resonance assisted hydrogen
bonds (RAHB) and topological parameters
The strength of a chemical bond is reflected in the electron
density at the bond critical point (ꢃBCP) which depends on the
nature of the bonded atoms. In general, ꢃBCP > 0 a.u. in shared

68
R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
Monomer
Dimer
Experimental
Dimer
Experimental
Monomer
500
1000
1500
3000
3500
4000
Wavenumber cm-1
Fig. 4. Correlation graph among experimental, calculated monomer and calculated dimer vibrational wavenumbers (in cm−1).
(covalent) bonding and less than 0.10 a.u. in a closed-shell inter-
action (ionic, van der Waals, hydrogen, dihydrogen, H H bonding
and other weak interactions). In covalent bonding the two neg-
ative curvatures are dominant and ꢀ2ꢃ(rBCP) < 0. In contrast, in
closed-shell bonding the interactions are characterized by a deple-
tion of density in the region of contact of the two atoms and
ꢀ2ꢃ(rBCP) > 0 [53]. The strength of the hydrogen bond could be sup-
ported further by Koch and Popelier criteria based on ‘atoms in
molecules’ theory: (i) the existence of bond critical point for the
proton (H)· · ·acceptor (A) contact as a confirmation of the exis-
tence of hydrogen bonding interaction; (ii) the value of electron
density (ꢃH· · ·A) should be within the range 0.002–0.040 a.u.; (iii)
the corresponding Laplacian ꢀ2ꢃ(rBCP) should be within the range
0.024–0.139 a.u. According to Rozas et al. [54] the interactions may
be classified as follows: (i) strong H-bonds are characterized by
ꢀ2ꢃ(rBCP) < 0 and HBCP < 0 and their covalent character is estab-
lished; (ii) medium H-bonds are characterized by ꢀ2ꢃ(rBCP) > 0 and
HBCP < 0 and their partially covalent character is established; (iii)
weak H-bonds are characterized by ꢀ2ꢃ(rBCP) > 0 and HBCP > 0 and
they are mainly electrostatic. The weak interactions are charac-
terized by ꢀ2ꢃ(rBCP) > 0 and HBCP > 0 and the distance between
interacting atoms is greater than the sum of van der Waals’ radii of
these atoms.
order
(H18· · ·O60 ≈ H64· · ·O9) > (H69· · ·O55 ≈ H22· · ·O10) >
(H74· · ·O9 ≈ H21· · ·O60) > (C6· · ·N14 ≈ C67· · ·N75) > (C7· · ·H45 ≈
C66· · ·H79).
In AIM theory, the binding energy of dimer is the sum of the
energies of all four intermolecular interactions and is calculated to
be equal to −15.41 kcal/mol. DFT is also applicable to calculate the
binding energy of dimer. From DFT, the binding energy of the dimer
is computed as the difference between the calculated total energy
of the dimer and the sum of the energies of two isolated monomers,
which is calculated as −14.32 kcal/mol.
The ellipticity (ε) at BCP is a sensitive index to monitor the
␲-character of bond. ε is related to ꢀ1 and ꢀ2, which correspond
to the eigen values of Hessian and defined by the relationship:
ε = (ꢀ1/ꢀ2) − 1. In order to investigate the effect of ␲-electron
delocalization in bonds associated with N and O atoms of both
(N H· · ·O C) intermolecular hydrogen bonds, the analysis of bond
ellipticity is performed. The ε values for bonds involved in sixteen-
membered pseudo ring are given in Table 5b. In this ring the
values of ε for bonds O9 C8, C8 C2, C2 C3, C3 C4, C4 C5,
C5 N1 associated with the N1 H18· · ·O60 and for bonds O60 C58,
C58 C59, C59 C62, C62 C65, C65 C63, C63 N61 associated with
the N61 H64· · ·O9 intermolecular hydrogen bonds are in the range
0.1011–0.2869. These values of ε correspond to the aromatic bonds
reported in literature [53,54]. This confirms that these intermolecu-
lar hydrogen bonds are resonance assisted hydrogen bonds (RAHB)
because both N and O atoms are interconnected by a system of
␲-conjugated double bonds.
According to both the values ꢀ2ꢃ(rBCP) > 0 and HBCP > 0 given
in Table 5a, the interactions C6· · ·N14, C67· · ·N75, C7· · ·H45,
C66· · ·H79 are weak. The interactions H18· · ·O60, H64· · ·O9,
H69· · ·O55, H22· · ·O10, H74· · ·O9, H21· · ·O60 are weak hydrogen
bonds. Interactions H74· · ·O9, H21· · ·O60 fulfill the two criteria of
hydrogen bonding i.e. ꢀ2ꢃ(rBCP) > 0 and HBCP > 0 but the criteria
of distance between interacting atoms are not fulfilled as this
distance is less than the sum of van der Waals’ radii of these atoms.
Therefore, interactions H74· · ·O9, H21· · ·O60 are in the category of
weak interactions. Five types of interactions are visualized in the
molecular graph of the dimer shown in Fig. 5. These interactions
are classified on the basis of geometrical (bond length, bond angle),
topological and energetic parameters. In this article, the Bader
3.6. Thermodynamic properties
On the basis of vibrational analysis of reactants and products,
the enthalpy change of reaction ( HReaction), Gibbs free energy
change of reaction ( GReaction) and entropy change of reaction
(
SReaction) are calculated and listed in Table 6. For the sake
of simplicity, reactants ethyl 4-acetyl-3,5-dimetyl-1H-pyrrole-2-
carboxylate and 3,5-dinitrobenzhydrazide and products PDNBAH
and water are abbreviated as A, B, C and D respectively. On the
basis of thermodynamic calculations G and H are positive and
S is negative, which indicates that the reaction is endothermic
and non-spontaneous at room temperature.
theory application is used to estimate hydrogen bond energy EHB
.
Espinosa proposed proportionality between hydrogen bond energy
(EHB) and potential energy density (VBCP) at H· · ·O bond critical
point: EHB = ½(VBCP) [55]. On the basis of electron density, bond
degree and interaction energy, their strength is in the following

R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
69
Fig. 5. Molecular graph of the dimer at the level of B3LYP/6-31G(d,p) using AIM program [bond critical points (small red spheres), ring critical points (small yellow sphere),
bond paths (pink lines)]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
Table 5a
Geometrical parameters and topological parameters for bonds of interacting atoms: electron density (ꢃBCP), Laplacian of electron density (ꢀ2ꢃ(rBCP), electron kinetic energy
density (GBCP), electron potential energy density (VBCP), total electron energy density (HBCP), bond degree ellipticity at bond critical point (BCP), estimated interaction energy
(Eint).
Bond length (A) ꢃBCP (a.u.) ꢀꢃ (×10−17 a.u.) ꢀ2ꢃ (a.u.) GBCP (a.u.) VBCP (a.u.) HBCP (a.u.)
Bond degree Ellipticity (ε)
Eint (kcal/mol)
˚
Interaction
between
atom no.
H18· · ·O60
H64· · ·O9
H69· · ·O55
H22· · ·O10
C6· · ·N14
1.90311
1.90313
2.35452
2.35458
2.95491
2.95491
2.60547
2.6055
0.02577
0.02577
0.01361
0.01361
0.01045
0.01045
0.00914
0.00914
0.00762
0.00762
0.7708
2.3465
0.07698
1.1615
1.8494
0.9727
1.8923
2.5049
0.07621
0.07998
0.082724
0.082718
0.048404
0.048402
0.041739
0.04174
0.037873
0.03787
0.026744
0.026736
0.02013
0.02013
0.01096
0.01096
0.00868
0.00868
0.00734
0.00734
0.00583
0.00583
−0.019587
−0.019586
−0.009813
−0.009812
−0.006928
−0.006928
−0.005216
−0.005216
−0.00498
0.000547
0.000547
0.001144
0.001144
0.001754
0.001754
0.002126
0.002126
0.000853
0.000853
13.31966
13.31966
52.74584
52.74584
105.3255
105.3255
145.9612
145.9612
70.24483
70.24483
0.01994
0.01996
0.19926
0.19938
0.31995
0.32206
1.0348
1.03462
0.16848
0.16855
−6.14551
−6.1452
−3.07888
−3.07856
−2.17369
−2.17369
−1.63654
−1.63654
−1.5625
C67· · ·N75
C7· · ·H45
C66· · ·H79
H74· · ·O9
H21· · ·O60
2.58206
2.58226
−0.004978
−1.56187

70
R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
Table 5b
flows from B to A; (ii) if ECT < 0, charge flows from A to B. ECT is
calculated using Eq. (6):
Calculated ellipticity parameter for bonds involved in sixteen membered pseudo
ring using AIM calculation.
ECT = ( Nmax
)
A − ( Nmax
)
(6)
Ring (C8 C2 C3 C4 C5 N1 H18· · ·O60 C58 C59 C62 C65 C63
N61 H66· · ·O9)
B
where ( Nmax
)
A = −ꢆA/ÁA.
Bond
Ellipticity
Bond
Ellipticity
ꢆB
O9 C8
C8 C2
C2 C3
C3 C4
C4 C5
C5 N1
N1 H18
H18· · ·O60
0.1011
0.2274
0.2869
0.2289
0.2642
0.1674
0.0305
0.0199
O60 C58
C58 C59
C59 C62
C62 C65
C65 C63
C63 N61
N61 H64
H64· · ·O9
0.1011
0.2274
0.2869
0.2289
0.2642
0.1674
0.0305
0.0199
(
Nmax
)
= −
B
ÁB
The calculated value of ECT < 0, for reactant molecules
ethyl 4-acetyl-3,5-dimetyl-1H-pyrrole-2-carboxylate (A) and 3,5-
dinitrobenzhydrazide (B) indicates charge flow from A to B.
Therefore, A acts as electron donor and B as electron acceptor. The
high value of chemical potential and low value of electrophilicity
index for A also favor its nucleophilic behavior. In the same way the
low value of chemical potential and high value of electrophilicity
index for B also favor its electrophilic behavior. The high value of
electrophilicity index for PDNBAH shows that it behaves as a strong
electrophile.
3.7. Chemical reactivity
3.7.1. Global reactivity descriptors
The energies of frontier molecular orbitals (εHOMO, εLUMO),
energy band gap (εHOMO − εLUMO), electronegativity (ꢅ), chemical
potential (ꢆ), chemical hardness (Á), global softness (S) and global
electrophilicity index (ω) [56–60] of PDNBAH have been listed in
Table 7a. On the basis of εHOMO, εLUMO these are calculated using
Eqs. (1)–(5) given below:
3.7.2. Local reactivity (descriptors)
Fukui functions (fk+, fk−, fk0), local softnesses (sk+, sk−, sk0) and
local electrophilicity indices (ωk+, ωk−, ωk0) [59,60] for selected
atomic sites in PDNBAH have been listed in Table 7b. Using
Hirshfeld atomic charges of neutral, cation and anion states of
PDNBAH, Fukui functions are calculated using the following equa-
tions ((7)–(9)).
1
ꢅ = − (εLUMO + εHOMO
)
(1)
(2)
(3)
(4)
2
1
2
ꢆ = −ꢅ = (εLUMO + εHOMO
)
+
fk = [q(N + 1) − q(N)] for nucleophilic attack
(7)
(8)
1
−
Á = (εLUMO − εHOMO
)
fk = [q(N) − q(N − 1)] for electrophilic attack
2
1
S =
1
2
0
fk
=
[q(N + 1) + q(N − 1)] for radical attack
(9)
2Á
ꢆ2
ω =
Local softnesses and electrophilicity indices are calculated using
the following equations ((10) and (11)).
(5)
2Á
+
−
0
+
−
0
Electrophilic charge transfer (ECT) [61] is defined as the differ-
ence between the Nmax values of interacting molecules. For two
molecules A and B approaching each other: (i) if ECT > 0, charge
sk = Sfk
,
sk = Sfk
,
sk = Sfk
(10)
(11)
+
−
0
+
−
0
ωk = ωfk
,
ωk = ωfk
,
ωk = ωfk
Table 6
Enthalpy, Gibbs free energy of reactants (A, B), products (C, D), reaction (in a.u.) and entropy of reactants (A, B), products (C, D), reaction (in cal/mol K).
A
B
C
D
Reaction
Enthalpy (H)
Gibb’s free energy (G)
Entropy (S)
−708.420315
−708.482028
129.886
−865.111275
−865.169110
121.725
−1497.124332
−1497.219327
199.934
−76.394588
−76.416024
45.116
0.01267
0.015787
−6.561
Table 7a
Calculated εHOMO, εLUMO, energy band gap (εL − εH), chemical potential (ꢆ), electronegativity (ꢅ), global hardness (Á), global softness (S), global electrophilicity index (ω) (in
eV) and electrophilicity-based charge transfer ECT for reactants A and B.
Molecule
εH
εL
εH–εL
ꢆ
ꢅ
Á
S
ω
ECT
Reactant (A)
Reactant (B)
Product (C)
−6.0315
−7.6391
−5.8197
−0.8158
−3.3065
−3.2256
−5.2157
−4.3326
2.5940
−3.424
−5.473
−4.5227
3.4237
5.4728
4.5227
2.60785
2.1663
1.2970
0.19173
0.23081
0.3854
2.2473
6.9131
7.8851
−1.2135
Table 7b
Using Hirshfeld population analysis: Fukui functions (fk+, fk−), Local softnesses (sk+, sk−) in eV, local electrophilicity indices (ωk+, ωk−) in eV for selected atomic sites of product
DNBAH.
Atom no.
Hirshfeld atomic charges
Fukui functions
Local softnesses
Local electrophilicity indices
+
−
+
−
+
−
ωk
qN
qN+1
qN−1
fk
fk
sk
sk
ωk
C8
0.196406
0.068978
0.173487
0.099555
0.074441
0.191201
0.050786
0.173037
0.086397
0.07505
0.216602
0.093915
0.195183
0.151426
0.144655
0.005205
0.018192
0.00045
0.013158
−0.00061
0.020196
0.024937
0.021696
0.051871
0.070214
0.002006
0.007011
0.000173
0.005071
−0.00023
0.007784
0.009611
0.008362
0.019991
0.02706
0.041042
0.143446
0.003548
0.103752
−0.0048
0.159247
0.196631
0.171075
0.409008
0.553644
C13
C16
N1
N15

R.N. Singh et al. / Spectrochimica Acta Part A 88 (2012) 60–71
71
where +, −, 0 signs show nucleophilic, electrophilic and radical
attack respectively.
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for synthesized molecule PDNBAH favor the formation of new het-
erocyclic compounds such as azetidinones and thiazolidinones by
attack of nucleophilic part of the dipolar reagent on the C13 site and
electrophilic part of dipolar reagent on the N14 site of C13 N14
bond. In the same way, the maximum values of all the three local
nucleophilic reactivity descriptors (fk−, sk−, ωk−) at N15 indicate
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PDNBAH is synthesized and characterized by 1H NMR,
UV–visible, FT-IR, DART-mass and elemental analyses. Theoreti-
cal electronic absorption spectra have some blue shifts compared
with the experimental data and molecular orbital coefficients’ anal-
ysis suggests that electronic transitions are assigned to ␲ → ␲*
type. In the present study, experimental and calculated vibra-
tional wavenumber analysis confirms the existence of dimer by
involvement of heteronuclear association through pyrrolic (N H)
and carbonyl (C O) oxygen of ester. The calculated binding ener-
gies of dimer using both DFT and AIM theory are −14.32 and
−15.41 kcal/mol respectively, indicating that both theories are in
good agreement with each other. AIM theory is more appropriate
than DFT since it is also applicable to calculate the heteronuclear
intermolecular hydrogen bond energy of dimer and it is calculated
as −12.29 kcal/mol. In addition, theoretical results from reactivity
descriptors for PDNBAH show most reactivity at C13 for nucle-
ophilic attack, hence it may be used as a precursor for the synthesis
of new heterocyclic compounds such as azetidinones and thiazo-
lidinones.
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Acknowledgements
The authors are thankful to the Directors of IIT Kanpur and CDRI
Lucknow for providing spectral measurements of PDNBAH and DST,
New Delhi for financial assistance.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.11.057.
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