Conformational, structural, vibrational and quantum chemical analysis on 4-aminobenzohydrazide and 4-hydroxybenzohydrazide-A comparative study

Article abstract of DOI:10.1016/j.saa.2013.01.076

Experimental and theoretical quantum chemical studies were carried out on 4-hydroxybenzohydrazide (4HBH) and 4-aminobenzohydrazide (4ABH) using FTIR and FT-Raman spectral data. The structural characteristics and vibrational spectroscopic analysis were carried performed by quantum chemical methods with the hybrid exchange-correlation functional B3LYP using 6-31G, 6-311++G and aug-cc-pVDZ basis sets. The most stable conformer of the title compounds have been determined from the analysis of potential energy surface. The stable molecular geometries, electronic and thermodynamic parameters, IR intensities, harmonic vibrational frequencies, depolarisation ratio and Raman intensities have been computed. Molecular electrostatic potential and frontier molecular orbitals were constructed to understand the electronic properties. The potential energy distributions (PEDs) were calculated to explain the mixing of fundamental modes. The theoretical geometrical parameters and the fundamental frequencies were compared with the experimental. The interactions of hydroxy and amino group substitutions on the characteristic vibrations of the ring and hydrazide group have been analysed.

Full text of DOI:10.1016/j.saa.2013.01.076

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Conformational, structural, vibrational and quantum chemical analysis on
4-aminobenzohydrazide and 4-hydroxybenzohydrazide – A comparative study
b
c
d
e
V. Arjunan a, , A. Jayaprakash , K. Carthigayan , S. Periandy , S. Mohan
⇑
a Department of Chemistry, Kanchi Mamunivar Centre for Post-Graduate Studies, Puducherry 605 008, India
b Department of Physics, Rajiv Gandhi College of Engineering and Technology, Puducherry 605 402, India
c Research and Development Centre, Bharathiar University, Coimbatore 641 046, India
d Department of Physics, Tagore Arts College, Puducherry 605 008, India
e Department of Physics, Hawassa University Main Campus, Hawassa, Ethiopia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The complete vibrational analyses of the fundamental modes of 4-hydroxybenzohydrazide (4HBH) and 4-
aminobenzohydrazide (4ABH) molecules were performed. The experimental parameters were compared
with the theoretical parameters of the compounds determined from the DFT–B3LYP gradient calculations
employing the 6-31Gꢀꢀ, 6-311++Gꢀꢀ and aug-cc-pVDZ basis sets. The effect of substituents ANH2 and
AOH in the benzohydrazide moiety have been analysed and compared. The kinetic and thermodynamic
stability and chemical hardness of the molecules have been determined. The reactive centres were found
from the molecular electrostatic potential of the molecules.
"
The vibrational analysis of 4-
hydroxybenzohydrazide and 4-
aminobenzohydrazide were
performed.
The experimental parameters were
compared with DFT–B3LYP
calculations.
The effect of ANH2 and AOH in the
benzohydrazide moiety have been
analysed.
Kinetic and thermodynamic
stabilities and chemical hardness of
the molecules were determined.
The reactive centres were found
from the electrostatic potential of
the molecules.
"
"
"
"
a r t i c l e i n f o
a b s t r a c t
Article history:
Experimental and theoretical quantum chemical studies were carried out on 4-hydroxybenzohydrazide
(4HBH) and 4-aminobenzohydrazide (4ABH) using FTIR and FT-Raman spectral data. The structural char-
acteristics and vibrational spectroscopic analysis were carried performed by quantum chemical methods
with the hybrid exchange-correlation functional B3LYP using 6-31Gꢀꢀ, 6-311++Gꢀꢀ and aug-cc-pVDZ basis
sets. The most stable conformer of the title compounds have been determined from the analysis of poten-
tial energy surface. The stable molecular geometries, electronic and thermodynamic parameters, IR inten-
sities, harmonic vibrational frequencies, depolarisation ratio and Raman intensities have been computed.
Molecular electrostatic potential and frontier molecular orbitals were constructed to understand the elec-
tronic properties. The potential energy distributions (PEDs) were calculated to explain the mixing of fun-
damental modes. The theoretical geometrical parameters and the fundamental frequencies were
compared with the experimental. The interactions of hydroxy and amino group substitutions on the char-
acteristic vibrations of the ring and hydrazide group have been analysed.
Received 8 December 2012
Received in revised form 29 January 2013
Accepted 31 January 2013
Available online 9 February 2013
Keywords:
4-Hydroxybenzohydrazide
4-Aminobenzohydrazide
FTIR
FT-Raman
NBO
MEP
Ó 2013 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +91 413 2211111, mobile: +91 9442992223; fax: +91 413 2251613.
E-mail address: varjunftir@yahoo.com (V. Arjunan).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.01.076

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
101
Introduction
High temperature resistive polymers have been the subject of
considerable investigation in recent years owing to their ability
to exhibit high thermo-oxidative stability, resistance to environ-
mental degradation, and superior dielectric, thermal, adhesive,
dimensional stability and mechanical properties [1–7]. These prop-
erties are strongly influenced by their chemical structure, i.e. by
both the chemical composition and molecular configuration. In
particular, polymers containing aromatic rings in the main chain
have received special attention as their presence makes these poly-
mers more thermally resistant [8–10]. In this connection, the intro-
duction of hydrazide or amide plus hydrazide linkages into the
backbone of the polymer chain is a viable alternative to improve
the processability of high temperature resistive polymers. Further,
the presence of hydrazide groups in the main chain can be
exploited by converting them into the more chemically resistant
and thermally stable oxadiazole structure by heating the polymer
in the bulk or fibre form at elevated temperatures [11]. Hydrazides
are known to have different biological activities [12–14].
Hydrazides are important starting materials for a wide range of
derivatives utilizable in pharmaceutical products and as surfac-
tants [15]. Hydrazides have been known to be associated with anti-
bacterial [16], antifungal [17], anthelmintic [18] and
anticonvulsant [19] activities. Biological assessment of fatty hydra-
zide and their derivatives have been studied [20,21]. Acylhydra-
zones, as an example of Schiff bases, and their metal complexes
have been widely studied due to their versatile applications in
the fields of analytical and medicinal chemistry and biotechnology
[22–24]. p-Hydroxy benzohydrazide moiety and its analogues are
suitable parent compounds upon which variety of biological activ-
ities were reported such as antitumor [25], antianginal [26], antitu-
bercular [27], antihypertensive [28] and antibacterial [29].
Scheme 2. Synthesis of 4-aminobenzohydrazide.
Fig. 1. Potential energy surface of 4-hydroxybenzohydrazide.
Fig. 2. Potential energy surface of 4-aminobenzohydrazide.
Generally the donor–acceptor substituted p-conjugated organic
molecules (e.g. nitroaniline) only exhibit large molecular nonlinear
optical (NLO) response. But there no experimental evidence of NLO
properties of benzohydrazide and its derivatives as such in the lit-
erature. NLO properties are not possible for the compounds under
investigation since they contain only donar groups. At the same
time benzohydrazide and its derivatives act as donar (ligand) in
the complexes which exhibits NLO properties [30,31]. The nonlin-
ear response in these molecules was found to increase with in-
crease in the donor strength of the substituted group.
Hydrazides have recently become attractive to theoreticians as
well as experimentalists due to the biological significance particu-
larly in medicinal and enzyme chemistry [32–37]. In continuation
of our earlier studies [38] and owing to the vast biological signifi-
cance and industrial applications of 4-aminobenzohydrazide
(4ABH) and 4-hydroxybenzohydrazide (4HBH) in an enormous
field, an extensive spectroscopic and structural study of these com-
pounds have been undertaken by recording their FTIR and FT-Ra-
man spectra and subjecting them to DFT analysis. The effects of
hydroxyl and amino groups on the characteristic frequencies of
the benzene ring moiety and hydrazide groups have been analysed.
Scheme 1. Synthesis of 4-hydroxybenzohydrazide.

102
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
Fig. 4. Various conformers of 4-aminobenzohydrazide.
Experimental
4-Hydroxybenzohydrazide (4HBH) was synthesised from the
corresponding acid through a conventional two step approach
(Scheme 1). All chemicals were obtained from Aldrich, U.S.A. and
were used without further purification. 3.45 g of hydroxybenzoic
acid is dissolved in 75 ml of dry ethanol and 2–3 drops of con.
H2SO4 are added, the mixture was stirred well for 2 h. The ester
4-hydroxyethylbenzoate was extracted with chloroform solvent
and evaporated by rotary evaporator. Then refluxing 4-hydrox-
yethylbenzoate (0.1 mol) with hydrazine hydrate (0.15 mol) in
Fig. 3. Possible conformers of 4-hydroxybenzohydrazide.
Thus, the novelty of the investigation is to provide more detailed
structural, conformational, vibrational, energies, stabilities and
thermodynamic properties of 4ABH and 4HBH.

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
103
Fig. 5. Structure and atom numbering of 4-hydroxybenzohydrazide (A) and 4-aminobenzohydrazide (B).
Table 1
Theoretical and experimental structural parameters of 4-aminobenzohydrazide and 4-hydroxybenzohydrazide.
Structural
parameters
4-Aminobenzohydrazide
Structural
parameters
4-Hydroxybenzohydrazide
Experimental
parametersa
B3LYP/6-
31Gꢀꢀ
B3LYP/6-
311++Gꢀꢀ
B3LYP/aug-cc-
pVDZ
B3LYP/6-
31Gꢀꢀ
B3LYP/6-
311++Gꢀꢀ
B3LYP/aug-cc-
pVDZ
Internuclear
distance (Å)
C1AC2
C2AC3
C3AC4
C4AC5
C5AC6
C6AC1
C1AC7
C7AO8
C7AN9
N9AN10
CAH (ring)b
NAH (hydrazide)b
1.403
1.390
1.407
1.408
1.387
1.403
1.499
1.221
1.389
1.402
1.086
1.014
1.401
1.389
1.404
1.406
1.385
1.401
1.499
1.216
1.386
1.399
1.084
1.011
1.405
1.393
1.408
1.409
1.390
1.405
1.499
1.222
1.388
1.403
1.090
1.014
C1AC2
C2AC3
C3AC4
C4AC5
C5AC6
C6AC1
C1AC7
C7AO8
1.406
1.387
1.400
1.399
1.392
1.402
1.494
1.229
1.387
1.406
1.084
1.017
1.403
1.386
1.397
1.397
1.391
1.399
1.494
1.224
1.386
1.406
1.083
1.015
1.409
1.389
1.403
1.401
1.395
1.405
1.500
1.229
1.387
1.403
1.090
1.021
1.385
1.386
1.377
1.379
1.378
1.380
1.473
1.229
1.365
1.372
0.930
0.860
C7AN9
N9AN10
CAH (ring)b
NAH
(hydrazide)b
C4AO11
O11AH12
NAH (amino)b
C4AN11
1.010
1.389
1.008
1.389
1.011
1.392
1.364
0.966
1.366
0.963
1.362
0.969
1.357c
0.80c
Bond angle (°)
C2AC1AC6
C2AC1AC7
C6AC1AC7
C1AC2AC3
C2AC3AC4
C3AC4AC5
C4AC5AC6
C1AC6AC5
118.1
124.3
117.6
121.1
120.5
118.4
120.6
121.3
120.2
118.6
120.0
119.5
120.8
120.7
119.4
120.0
118.1
120.7
122.4
114.2
123.4
119.0
116.2
118.6
111.1
108.9
109.2
118.0
124.2
117.7
121.2
120.5
118.4
120.6
121.2
120.4
118.4
119.9
119.6
120.8
120.7
119.5
119.9
118.3
120.4
122.4
114.2
123.3
119.9
117.4
118.7
111.9
110.1
110.6
116.9
113.3
118.0
124.1
117.8
121.2
120.5
118.5
120.6
121.3
120.5
118.3
119.9
119.6
120.7
120.7
119.6
119.9
118.3
120.4
122.3
114.6
123.1
119.4
116.9
118.4
111.5
109.4
109.7
116.7
113.2
C2AC1AC6
C2AC1AC7
C6AC1AC7
C1AC2AC3
C2AC3AC4
C3AC4AC5
C4AC5AC6
C1AC6AC5
C1AC2AH14
C3AC2AH14
C2AC3AH15
C4AC3AH15
C3AC4AO11
C5AC4A O11
C4AC5AH16
C6AC5AH16
C1AC6A H17
C5AC6A H17
C1AC7AO8
118.4
125.6
115.9
120.6
120.2
119.4
120.0
121.4
119.9
119.5
119.9
119.9
122.6
117.5
119.0
121.5
118.0
120.5
121.4
121.1
117.5
123.9
110.5
118.8
108.9
110.6
108.4
109.1
118.5
124.9
116.5
120.6
120.1
119.1
120.2
121.3
120.0
119.5
119.9
120.0
122.6
117.5
119.1
121.3
118.4
120.2
121.4
120.6
118.0
124.0
111.6
118.6
109.5
111.0
109.3
109.8
118.1
126.5
115.3
120.7
120.4
119.6
119.7
121.6
119.6
119.6
119.8
119.8
122.8
117.6
118.9
121.5
117.8
120.6
121.0
121.9
117.7
124.8
110.7
119.2
108.8
110.4
107.3
108.8
121.1
119.5
119.5
120.5
119.2
119.8
119.8
118.1
120.0
121.1
119.9
119.9
1195
119.5
119.5
119.5
118.5
123.4
121.7
115.7
122.5
121.0
121.0
118.1
C1AC2AH14
C3AC2AH14
C2AC3AH15
C4AC3AH15
C3AC4AN11
C5AC4AN11
C4AC5AH16
C6AC5AH16
C1AC6AH17
C5AC6AH17
C1AC7AO8
C1AC7AN9
O8AC7AN9
C7AN9AN10
C7AN9AH18
N10AN9AH18
N9AN10AH19
N9AN10AH20
H19AN10AH20
C1AC7AN9
O8AC7AN9
C7AN9AN10
C7AN9AH13
N10AN9AH13
N9AN10AH18
N9AN10AH19
H18AN10AH19
C4AO11AH12
C4A NAH (amino)b 116.2
H12AN11AH13 112.8
109.5c
a
b
c
Values taken from Ref. [48].
Mean value.
Values taken from Ref. [39].
75 ml of dry ethanol for 5–6 h to form benzohydrazide. The prod-
uct was filtered, washed with hexene and dried. The product was
recrytallised with methanol and dried in air. The melting point of
4-hydroxybenzohydrazide is 265 °C. All elemental analysis (C, H,

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V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
Table 2
The thermodynamic parameters of 4-aminobenzohydrazide and 4-hydroxybenzohydrazide.
Thermodynamic parameters (298 K)
4-Aminobenzohydrazide
B3LYP
4-Hydroxybenzohydrazide
B3LYP
6-31Gꢀꢀ
6-311++Gꢀꢀ
aug-cc-pVDZ
6-31Gꢀꢀ
6-311++Gꢀꢀ
aug-cc-pVDZ
Total energy (thermal), Etotal (kcal molꢁ1
)
107.69
39.66
99.35
107.19
40.00
100.02
107.03
40.08
100.23
99.91
37.75
97.94
99.41
38.06
98.27
99.52
37.70
98.68
Heat capacity at const. volume, Cv (kcal molꢁ1 Kꢁ1
)
Entropy, S (kcal molꢁ1 Kꢁ1
)
Vibrational energy, Evib (kcal molꢁ1
)
105.92
105.42
105.25
98.13
97.63
97.75
SCF (Hartrees)
Rotational constants (GHz)
ꢁ511.6349
ꢁ511.7750
ꢁ511.6993
ꢁ531.4991
ꢁ531.6463
ꢁ531.5224
X
Y
Z
3.35
0.56
0.49
3.36
0.56
0.49
3.35
0.56
0.49
2.51
0.66
0.54
2.51
0.66
0.54
2.52
0.66
0.53
Dipolemoment (Debye)
lx
ly
lz
ꢁ2.90
ꢁ4.33
3.19
ꢁ3.01
ꢁ4.42
2.91
ꢁ3.01
ꢁ4.29
2.84
0.84
ꢁ4.69
1.00
0.69
ꢁ4.89
0.89
0.92
ꢁ4.75
0.61
ltotal
6.11
6.09
5.96
4.86
5.02
4.87
Fig. 6. Temperature dependence of entropy of 4-hydroxybenzohydrazide (4HBH)
Fig. 8. Temperature dependence of enthalpy change of 4-hydroxybenzohydrazide
and 4-aminobenzohydrazide (4ABH).
(4HBH) and 4-aminobenzohydrazide (4ABH).
Table 3
The energy of frontier molecular orbitals of 4-aminobenzohydrazide and 4-hydrox-
ybenzohydrazide determined by DFT methods.
Energy level
4-
4-
Aminobenzohydrazide
B3LYP
Hydroxybenzohydrazide
B3LYP
6-
aug-cc-
6-
aug-cc-
pVDZ
311++Gꢀꢀ pVDZ
311++Gꢀꢀ
ELUMO (a.u.)
ꢁ0.0341
ꢁ0.2216
0.1875
ꢁ0.0355
ꢁ0.0409
ꢁ0.2378
0.1969
ꢁ0.0261
ꢁ0.2254
0.1993
EHOMO (a.u.)
Eg = ELUMO ꢁ EHOMO
(a.u.)
ꢁ0.2211
0.1856
ELUMO+1 (a.u.)
EHOMOꢁ1 (a.u.)
Eg = ELUMOꢁ1 ꢁ EHOMO+1
(a.u.)
ꢁ0.0231
ꢁ0.2517
0.2286
ꢁ0.0240
ꢁ0.2495
0.2255
ꢁ0.0241
ꢁ0.2604
0.2363
ꢁ0.0054
ꢁ0.2449
0.2395
4-Aminobenzohydrazide (4ABH) was synthesised using the re-
ported procedure [39] by Scheme 2. 1.0 g of 1,4-bis(4-nitro-
benzoyloxymethyl)benzene and 10 ml of hydrazine monohydrate
were added in 80 ml of ethanol and refluxed for an hour. Then
0.2 g of 5% palladium on carbon (Pd/C) was added and further re-
fluxed for 15 h and filtered hot to remove Pd/C. Then it is allowed
to cool and the crude solid was recrystallised from ethanol and
dried in air to afford 4-aminobenzohydrazide. The melting point
Fig. 7. Temperature dependence of heat capacity at constant pressure of 4-
hydroxybenzohydrazide (4HBH) and 4-aminobenzohydrazide (4ABH).
N) were carried out on a Perkin Elmer 2400 CHN elemental ana-
lyser. The calculated (found)% for C7H8N2O2: C, 54.55 (53.85); H,
5.26 (5.11) and N, 18.42 (18.10).

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
105
Table 4
Atomic charges of 4-hydroxybenzohydrazide and 4-aminobenzohydrazide calculated
by NBO at B3LYP/6-311++Gꢀꢀ level.
Atom
4-Hydroxybenzohydrazide
4-Aminobenzohydrazide
C1
C2
C3
C4
ꢁ0.1747
ꢁ0.1373
ꢁ0.2907
0.3345
ꢁ0.1781
ꢁ0.1360
ꢁ0.2633
0.1871
C5
C6
C7
ꢁ0.2557
ꢁ0.1339
0.6682
ꢁ0.2562
ꢁ0.1302
0.6545
O8
N9
ꢁ0.6265
ꢁ0.4781
ꢁ0.6398
ꢁ0.6669
ꢁ0.5986
ꢁ0.5076
ꢁ0.6283
N10
O11
N11
H12
H13
H14
H15
H16
H17
H18
H19
H20
ꢁ0.7813
0.3745
0.3753
0.2019
0.1977
0.2007
0.2318
0.3602
0.3545
0.3414
0.4672
0.3682
0.2181
0.2005
0.2198
0.2286
0.3503
0.3483
Fig. 9. Frontier molecular orbital of 4-hydroxybenzohydrazide (A) and 4-amin-
obenzohydrazide (B).
of 4-aminobenzohydrazide is 226 °C. All elemental analysis (C, H,
N) were carried out on a Perkin Elmer 2400 CHN elemental ana-
lyser. The calculated (found)% for C7H8N2O2: C, 55.63 (55.25); H,
5.96 (5.92) and N, 27.81 (27.75).
module equipped with Nd:YAG laser source with 200 mW power
operating at 1.064
m. The spectral resolution is 2 cmꢁ1
l
.
The FTIR spectra of 4ABH and 4HBH have been recorded in the
region between 4000 and 400 cmꢁ1 by KBr disc method using Bru-
ker IFS 66 V spectrometer. A KBr beam splitter and liquid nitrogen
cooled MCT detector were used to collect the mid-infrared spectra.
The FT-Raman spectra were also recorded in the range between
4000 and 100 cmꢁ1 by the same instrument with FRA 106 Raman
Computational details
The gradient corrected density functional theory (DFT) with the
three-parameter hybrid functional Becke3 (B3) [40,41] for the ex-
change part and the Lee–Yang–Parr (LYP) correlation functional
[42] level of calculations have been carried out in the present
Fig. 10. MESP and electrostatic potential contour maps of 4-hydroxybenzohydrazide (A and B) and 4-aminobenzohydrazide (C and D).

106
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
tion program [45] has been utilised to construct the optimised
molecular structures, MEP surface and the shape of HOMO and
LUMO orbitals.
The Raman scattering activities (Si) calculated by Gaussian 03W
program were suitably converted to relative Raman intensities (Ii)
using the following relationship derived from the basic theory of
Raman scattering [46].
4
fðm0
ꢁ
miÞ Si
Ii ¼
mi½1 ꢁ expðꢁhc
m
i=kTÞꢂ
where vi is the vibrational wave-
v
0 is the exciting frequency (cmꢁ1),
number of the ith normal mode, h, c and k are universal constants,
and f is the suitably chosen common scaling factor for all the peak
intensities.
Results and discussion
Conformational analysis
Fig. 11. Atomic charges correlation graph between 4-hydroxybenzohydrazide and
4-aminobenzohydrazide.
To find all possible conformers and also the most stable geom-
etry of 4HBH and 4ABH molecules conformation analysis was car-
ried out by using B3LYP/6-311++Gꢀꢀ method. During the potential
energy surface scan, all the geometrical parameters were simulta-
neously relaxed while the dihedral angle O8AC7AN9AH13 of
4HBH and O8AC7AN9AH18 of 4HBH are varied in steps of 15°
ranging from 0° to 360°. The potential energy surface of 4HBH
and 4ABH were shown in Figs. 1 and 2, respectively. The energy
profile of 4HBH shows five conformers A, B, C, D and E with relative
energies 0.0, 16.548, 0.856, 1.201 and 10.907 kcal molꢁ1, respec-
tively have been shortlisted and are shown in Fig. 3. For 4ABH mol-
ecule four conformers A, B, C and D with relative energies 0.00,
10.383, 0.695, and 1.112 kcal molꢁ1, respectively have been short-
listed and are shown in Fig. 4. Thus, the optimised geometry (A) in
Figs. 3 and 4 corresponds to global minimum energy in the PES be-
longs to the most stable conformer of 4HBH and 4ABH molecules.
The geometrical parameters, electronic, thermodynamic properties
and vibrational frequencies were determined by B3LYP method
with 6-31Gꢀꢀ, 6-311++Gꢀꢀ and aug-cc-pVDZ basis sets.
investigation, using 6-31Gꢀꢀ, 6-311++Gꢀꢀ and aug-cc-pVDZ basic
sets with Gaussian-03W [43] program.
The conformational analyses were performed and the energies
of the different possible conformers were found. The geometry of
the different conformers of the compounds were optimised with
B3LYP method using 6-31Gꢀꢀ, 6-311++Gꢀꢀ and aug-cc-pVDZ basis
sets to characterise all stationary points as minima. The optimised
structural parameters of the most stable conformer were used in
the vibrational frequency calculations. The potential energy distri-
butions corresponding to each of the observed frequencies were
calculated with the program of Fuhrer et al. [44].
Isoelectronic molecular electrostatic potential have been calcu-
lated using 6-311++Gꢀꢀ basis set. The molecular electrostatic po-
tential (MEP) at a point r in the space around a molecule (in
atomic units) can be expressed as:
Z
0
0
X
~
ZA
q
ðr Þdr
VðrÞ ¼
ꢁ
0
~
~
~
jr ꢁ rj
~
jRA ꢁ rj
A
Molecular geometry and structural properties
where ZA is the charge on nucleus A, located at RA and
q
(r0) is the
electronic density function for the molecule. The first and second
terms represent the contributions to the potential due to nuclei
and electrons, respectively. V(r) is the resultant at each point r,
which is the net electrostatic effect produced at the point r by both
the electrons and nuclei of the molecule. GaussView 5.0.8 visualisa-
The energetically most stable optimised geometry of 4HBH and
4ABH obtained from B3LYP/6-311++Gꢀꢀ method and the scheme of
numbering the atoms are shown in Fig. 5. The geometry of the
most stable configuration of the molecules posses C1 point group
symmetry. All vibrations are active in both IR and Raman.
Table 5
Second order perturbation theory analysis of Fock matrix by B3LYP/6-311++Gꢀꢀ method.
Donor (i) ? acceptor (j)
4-Aminobenzohydrazide
4-Hydroxybenzohydrazide
E(2)a (kJ molꢁ1
)
E(j) ꢁ E(i)b (a.u.)
F(I,j)e (a.u.)
E(2)a (kJ molꢁ1
)
E(j) ꢁ E(i)b (a.u.)
F(I,j)e (a.u.)
p
p
p
p
p
p
p
(C1AC2) ? pꢀ(C3AC4)
(C1AC2) ? p⁄(C5AC6)
(C1AC2) ? pꢀ(C7AO8)
(C3AC4) ? pꢀ(C1AC2)
(C3AC4) ? pꢀ(C5AC6)
(C5AC6) ? pꢀ(C1AC2)
(C5AC6) ? pꢀ(C3AC4)
16.64
22.39
16.81
25.35
14.55
15.79
23.35
18.53
27.74
37.39
29.11
0.27
0.29
0.31
0.29
0.29
0.28
0.28
0.67
0.67
0.34
0.32
0.061
0.072
0.066
0.076
0.059
0.061
0.074
0.101
0.123
0.101
0.092
16.96
22.6
16.54
24.4
14.51
15.98
24.58
17.38
24.21
32.13
0.27
0.28
0.33
0.3
0.061
0.073
0.068
0.077
0.06
0.061
0.074
0.099
0.116
0.098
0.3
0.29
0.27
0.68
0.68
0.37
n(O8) ? rꢀ(C1AC7)
n(O8) ? rꢀ(C7AN9)
n(N9) ? pꢀ(C7AO8)
n(N11) ? pꢀ(C3AC4)
n(O11) ? pꢀ(C3AC4)
28.43
0.35
0.096
a
b
e
Stabilisation (delocalization) energy.
Energy difference between i(donor) and j(acceptor) NBO orbitals.
Fock matrix element i and j NBO orbitals.

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
107
Fig. 12. FTIR spectrum of (A) 4-aminobenzohydrazide and (B) 4-hydroxybenzohydrazide.
Fig. 13. FT-Raman spectrum of (A) 4-aminobenzohydrazide and (B) 4-hydroxybenzohydrazide.

108
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
The optimised structural parameters for the thermodynamically
For 4ABH the corresponding relations are
preferred geometry of 4HBH and 4ABH determined at B3LYP meth-
od using 6-31Gꢀꢀ, 6-311++Gꢀꢀ and aug-cc-pVDZ basis sets are pre-
sented in Table 1. The parameters derived from B3LYP/6-311++Gꢀꢀ
method were only considered for comparative discussion of the
compounds due to the more reliability of this method. In 4ABH
the mean planes of the benzene ring and the planar hydrazide
group are inclined at 28.6° with respect to each other. But the
mean planes of the benzene ring and the planar hydrazide group
of 4HBH are inclined at 24.5° with respect to each other. Except
amino and hydrazide hydrogens, the 4ABH and 4HBH molecules
are essentially planar as evidenced by the torsion angles
C6AC1AC7AO8, N10AN9AC7AC1 and N10AN9AC7AO8 of
ꢁ22.6°, ꢁ178.8° and 1.0° for 4ABH while these are ꢁ23.3°,
ꢁ23.2° and 158.5°, respectively for 4HBH molecule.
S ¼ 215:66442 þ 0:76155T ꢁ 2:40543 ꢃ 10ꢁ4T2
Cp ¼ 17:09554 þ 0:62815T ꢁ 2:81717 ꢃ 10ꢁ4T2
D
H ¼ ꢁ1:85155 þ 0:04736T þ 2:1198 ꢃ 10ꢁ4T2
The regression factors (R2) for all the relations are 0.999. Figs. 6–
8 one can observe that the difference between the respective ther-
modynamic functions of 4HBH and 4ABH are directly proportional
to the temperature.
Electronic properties
The energy of HOMO, LUMO, LUMO+1 and HOMOꢁ1 and their
orbital energy gap of 4HBH and 4ABH are calculated using
B3LYP/6-311++Gꢀꢀ method is given in Table 3. The pictorial illus-
trations of the frontier molecular orbitals are shown in Fig. 9. The
positive and negative phase is represented in red and green1 col-
our, respectively. The region of HOMO and LUMO levels spread over
the entire molecule and the calculated energy gap of HOMO–LUMO’s
explains the ultimate charge transfer interface within the molecule.
The frontier orbital energy gaps Eg = ELUMO ꢁ EHOMO in case of 4HBH
and 4ABH is found to be 0.1969 and 0.1875 a.u., respectively. The
The aromatic CAH, NAH (hydrazide) and NAH (amino) dis-
tances of 4ABH are 1.084, 1.011 and 1.008 Å, respectively. In
4HBH the aromatic CAH, OAH and NAH distances are 1.083,
0.963 and 1.015 Å, respectively. The mean CAC bond distance of
the ring carbon atoms of 4HBH and 4ABH are 1.413 and 1.412 Å,
respectively. The CAH bond lengths are found to be insignificant
deviation with the AOH and ANH2 substitutions. The electron dif-
fraction study of benzohydrazide shows the mean CAC (ring) bond
distance, the CAH, C@O and CAO bond distances 1.396, 0.930,
1.229 and 1.358 Å, respectively [38]. The presence of AOH and
ANH2 substitutions leads insignificant distortion in bond lengths
of the benzene ring while a slight significant distortion is absorbed
in the substituent bond angles. The CANAH bond angle where the
ANH2 group is attached with the carbon C4 is nearly 117° while
the CAOAH bond angle to the substituent AOH is found to be
nearly 109°.
In 4ABH, the angles about the carbonyl carbon atom (C7) ranges
from 114.2 for N9AC7AC1 to 122.4 for O8AC7AC1, consistent with
significant carbonyl character in the C7@O8 bond (1.216 Å). In the
case of 4HBH these angles are equal to 120.6° and 121.4°, respec-
tively. The N9AC7 bond distance of 4ABH is 1.386 Å and
N9AN10 is 1.399 Å while in 4HBH these angles are 1.386° and
1.406°, respectively. These structural parameters are in good
agreement with the literature [38,39,47,48].
HOMO and LUMO reveals that there are both
p ?
pꢀ and n ? pꢀ
charge transfer transitions in these molecules. The absolute chemical
hardness has been used as a measure of kinetic stability or the reac-
tivity of the molecule. The chemical hardness measured from the
frontier molecular orbital energies of 4HBH and 4ABH is 0.09845
and 0.09375 eV, respectively. The smaller Eg and the hardness signify
the high reactivity of the molecules.
The value of the electrostatic potential mapped onto an electron
iso-density surface may be employed to distinguish regions on the
surface which are electron rich (subject to electrophilic attack)
from those which are electron deficient (subject to nucleophilic at-
tack). The resulting surface simultaneously displays molecular size,
shape and electrostatic potential in terms of colour grading and is
very useful tool in investigation of correlation between molecular
structure and the physiochemical property relationship of mole-
cules including biomolecules and drugs [50,51]. The equation used
to find the electrostatic potential is,
Temperature dependence of thermodynamic properties
The frequency calculations compute the zero point energies,
thermal correction to internal energy, enthalpy, Gibbs free energy
and entropy as well as the heat capacity for a molecular system.
The calculated thermodynamic parameters of 4HBH and 4ABH
employing B3LYP method with 6-31Gꢀꢀ, 6-311++Gꢀꢀ and aug-cc-
pVDZ basis sets are presented in Table 2.
Total electrostatic potential energy
X
¼
Electrostatic potential energy
q1q
r
Potential energy ¼ K
2 ; K ¼ Coulomb’s constant
MEP and electrostatic potential contour maps of 4-hydrox-
ybenzohydrazide (A and B) and 4-aminobenzohydrazide (C and
D) are depicted in Fig. 10. The colour scheme of MEP is the negative
electrostatic potentials are shown in red, the intensity of which is
proportional to the absolute value of the potential energy, and po-
sitive electrostatic potentials are shown in blue while green indi-
cates surface areas where the potentials are close to zero. The
colour-coded values are then projected onto the 0.002 a.u. isoden-
sity surface to produce a three-dimensional electrostatic potential
model. The oxygen atoms with lone pairs have more negative elec-
trostatic potentials (red) whereas the hydrazide hydrogen atoms
posses positive electrostatic potentials (blue). Green areas cover
parts of the molecule where electrostatic potentials are close to
zero (CAC and CAH bonds). Such a representation provides more
detailed information regarding electrostatic potential distribution,
The temperature dependence of the thermodynamic
properties heat capacity at constant pressure (Cp), entropy (S)
and enthalpy change (DH0?T) for the compounds were also
determined by B3LYP/6-311++Gꢀꢀ method. The anharmonicity ef-
fects have been eliminated by scaling the thermodynamic prop-
erties by 0.98. Figs. 6–8 depicts the correlation of heat capacity
at constant pressure (Cp), entropy (S) and enthalpy change
(DH0?T) with temperature. The figures reveal that the entropies,
heat capacities, and enthalpy changes are increasing with
temperature ranging from 50 to 700 K [49]. The observed rela-
tions of the thermodynamic functions vs. temperatures for
4HBH are
S ¼ 218:46431 þ 0:72186T ꢁ 2:22077 ꢃ 10ꢁ4T2
Cp ¼ 21816:15762 þ 0:59834T ꢁ 2:61755 ꢃ 10ꢁ4T2
1
For interpretation of color in Figs. 9 and 10, the reader is referred to the web
D
H ¼ ꢁ1:55124 þ 0:04358T þ 2:05264 ꢃ 10ꢁ4T2
version of this article.

Table 6
The Experimental FTIR and FT-Raman frequencies, calculated frequencies, force field along with their relative intensities, probable assignments and potential energy distribution (PED) of 4-hydroxybenzohydrazide.a
Experimental
wavenumber
B3LYP/6-311++G(d,p) calculated
wavenumber
B3LYP/6-31G(d,p) calculated wavenumber
B3LYP/aug-cc-pVDZ Calculated
wavenumber
Depolarisation
ratio
%PED
(cmꢁ1
FTIR
)
FTR
Unscaled
Scaled
IR
Unscaled
Scaled
IR
Raman
intensity
Unscaled
Scaled
IR
(cmꢁ1
)
(cmꢁ1
)
intensity
(cmꢁ1
)
(cmꢁ1
)
intensity
(cmꢁ1
)
(cmꢁ1
)
intensity
3428 s
3320 vs 3329vw 3563
3280 m 3256vw 3520
3831
3448
3314
3274
3227
3101
3076
3062
3025
1634
1638
1598
1573
1495
1429
1416
76.77
6.97
22.62
2.03
2.45
3.39
3818
3560
3517
3460
3254
3226
3210
3165
1755
1696
1667
1636
1557
1482
1468
3436
3311
3271
3218
3091
3065
3050
3007
1632
1628
1600
1571
1495
1423
1409
53.79
1.42
10.17
4.74
2.27
3.66
0.729
0.528
0.832
1.000
0.343
0.506
0.389
0.505
0.254
0.112
0.501
0.074
0.053
0.143
0.051
3774
3568
3486
3420
3251
3221
3199
3155
1740
1674
1663
1631
1543
1473
1458
3434
3354
3277
3215
3088
3060
3039
2997
1618
1624
1613
1582
1497
1429
1414
65.07
1.67
11.25
4.17
2.73
2.86
0.28
0.70
0.23
0.15
0.23
0.17
0.50
0.31
0.17
0.72
0.47
0.47
0.48
0.20
0.23
93
91
95
94
92
90
94
90
95
m
m
m
m
m
m
m
m
m
OH
aNH2
NH
sNH2
CH
CH
CH
CH
C@O
3202 m
3470
3230
3204
3190
3151
3081 w
1.86
3.57
4.50
3012 w
1622 vs 1623 vs 1720
17.66
286.41
50.39
147.14
63.72
43.11
20.59
9.27
21.12
222.41
27.66
141.00
53.50
32.79
15.73
26.39
21.20
225.31
21.11
148.08
54.46
35.70
30.32
27.30
1607 s
1591 s
1539 m
1512 s
1467 m
1612 s
1590 s
1689
1647
1622
1541
1473
1460
89dNH2
85
79
80
82
m
m
m
m
CC
CC
CC
CC
1396 m 1397
vw
75bNH + 1 9bC@O
1340 w
1329 m 1329 m 1362
1332
1282 m
1257 vs 1255
vw
1342 m 1371
1330
1321
1292
1272
1246
149.64
177.65
0.62
6.75
116.00
1390
1380
1338
1316
1313
1334
1325
1284
1263
1260
147.95
194.75
5.69
48.35
48.62
0.133
0.138
0.004
0.049
0.021
1390
1381
1320
1315
1308
1348
1340
1280
1276
1269
127.06
209.74
12.77
8.86
0.30
0.32
0.54
0.47
0.10
81
85
83
78
m
m
m
m
CC
CN
CC
CC
1311
1285
68.00
71bOH + 1 9bCAO
1175 s
1185 vs 1200
1194
1164
1158
1149
1095
1056
6.34
3.13
286.67
15.77
15.32
1207
1202
1193
1134
1096
1159
1154
1145
1089
1052
9.84
0.015
0.024
0.120
0.005
0.028
1204
1197
1180
1118
1089
1168
1161
1145
1084
1056
1.76
0.29
0.72
0.15
0.54
0.31
70
65bCH + 22bCAO
85 CO
62bCH + 16bCCC
60bCH + 20bCCC
mNN + 1 9bNAH
24.27
267.57
13.45
9.29
163.24
132.49
12.00
9.73
1140 m 1152 s
1090 w
1049
vw
1185
1129
1089
m
1046
vw
995 m
1028
990
952
897
860
845
813
775
710
692
667
649
588
556
508
422
414
372
340
312
297
235
997
960
923
870
834
820
789
752
689
671
647
630
570
539
493
409
402
361
330
303
288
228
1.93
1.56
0.73
1030
989
948
923
860
851
814
770
715
695
676
652
592
555
515
424
416
379
372
320
298
243
989
949
910
886
826
817
781
739
686
667
649
626
568
533
494
407
399
364
357
307
286
233
1.50
1.39
0.99
0.003
0.007
0.010
0.024
0.016
0.134
0.023
0.006
0.014
0.017
0.030
0.025
0.022
0.001
0.002
0.002
0.001
0.017
0.015
0.006
0.010
0.004
1023
1011
979
934
872
849
822
784
710
691
667
646
592
552
521
426
413
396
370
321
293
250
992
981
950
906
846
824
797
760
689
670
647
627
574
535
505
413
401
384
359
311
284
243
1.64
0.88
4.09
0.26
0.61
0.71
0.63
0.34
0.09
0.74
0.75
0.47
0.19
0.49
0.68
0.46
0.61
0.73
0.56
0.33
0.74
0.45
0.68
0.33
0.67
59bCCC + 19bC@O
52bCH + 24bCC
899 m
851 s
899 w
50
53
49
48
55
c
CH + 18
c
CCC
175.30
28.29
12.15
4.66
43.33
33.08
1.92
18.66
20.88
50.91
16.84
9.32
0.89
15.71
2.05
107.22
42.65
14.00
6.96
160.06
18.68
12.32
5.48
50.04
43.64
1.11
17.33
15.55
42.94
14.00
4.35
133.02
18.36
14.07
4.71
32.60
32.62
0.30
11.83
25.10
41.03
13.31
6.12
qNH2 + 24bNH
c
c
c
CH + 25
CH + 22
CH + 20
c
c
c
CCC
CCC
CCC
819 vw
768 m
824 w
774 vw
50bCCC + 21bNH
46bCCC + 29bCH
66bC@O + 19bNH
652 m
631 s
659 vw
641 vw
60
52
c
c
NH + 15
OH + 22
c
c
C@O
CO
49bCN + 23bC@O
45bCC + 21bNH
42bCC + 19bC@O
525 w
487 w
525 vw
495 vw
0.83
2.47
51
43
42
45
46
41
c
c
c
c
s
c
C@O + 17cNH
16.41
114.40
7.60
36.72
18.06
10.33
16.73
102.00
2.44
24.00
19.65
15.54
CCC + 22
c
CO
359 w
334 w
297 vw
CCC + 21
c
CH
CN + 35
NH2 + 27
CC + 25 NH
c
C@O
c
NH
c
224 vw
50bNN(H2) +
(continued on next page)

110
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
by showing the values in a manifold of spatial location around the
molecule. The maximum values of positive and negative potential
are 0.0835e and ꢁ0.1055e, respectively for 4ABH while 0.1149e
and ꢁ0.1028e for 4HBH.
Natural bond orbital analysis
The atomic charges of 4HBH and 4ABH calculated by NBO anal-
ysis using the B3LYP/6-311++Gꢀꢀ method is presented in Table 4.
The correlation of the atomic charges of 4HBH and 4ABH are illus-
trated in Fig. 11. In the ring carbon atoms C4 in 4HBH and 4ABH
connected to the electronegative O11 and N11, respectively have
positive charge while other carbons have negative charges. The
greater positive charge of C7 indicates the polar nature of the
C@O group. The very high positive charge resides on the hydrazide,
hydroxy and amino hydrogen atoms and is due to the difference in
electronegativity of these atoms with oxygen and nitrogen atoms,
respectively. The significant variation of the charges of C4 atom in
these compounds is due to the AOH and ANH2 substitutions.
Donor–acceptor interactions
Natural bond orbital (NBO) analysis is a useful tool for under-
standing delocalisation of electron density from occupied Lewis–
type (donor) NBOs to properly unoccupied non-Lewis type (accep-
tor) NBOs within the molecule. The bonding–antibonding interac-
tion can be quantitatively described in terms of the NBO approach
that is expressed by means of second-order perturbation interac-
tion energy E(2) [52–54]. This energy represents the estimate of
the off-diagonal NBO Fock matrix element. The stabilisation energy
E(2) associated with i (donor) ? j (acceptor) delocalisation is esti-
mated from the second-order perturbation approach [54] as given
below
F2ði; jÞ
Eð2Þ ¼ q
i ej
ꢁ
ei
where qi is the donor orbital occupancy, ei and ej are diagonal ele-
ments (orbital energies) and F(i,j) is the off-diagonal Fock matrix
element.
The second order perturbation analysis of Fock matrix of 4ABH
and 4HBH with different types of donor–acceptor interactions and
their stabilisation energy are summarised in Table 5. All lone pair–
bond pair interactions and only bond pair–bond pair interactions
with stabilisation energy greater than 14 kJ molꢁ1 are listed Ta-
ble 5. In 4ABH molecule, the bond pair donor orbi-
tal, pCC
!
pꢀCC interaction between the C3AC4 bond pair and the
C1AC2 antibonding orbital gives strongest stabilisation of
25.35 kJ molꢁ1, C5AC6 bond pair and the C3AC4 antibonding orbi-
tal gives strong stabilisation of 23.35 kJ molꢁ1
.
In 4HBH the bond pair donor orbital, pCC
tween the C3AC4/C5AC6 bond pair and the C1AC2/C3AC4 anti-
bonding orbital gives strongest stabilisation of 24.4 kJ molꢁ1
C1AC2 bond pair and the C3AC4/C7AO8 antibonding orbital
pꢀCO interaction gives strong stabilisation of 16.96 and
!
pꢀCC interaction be-
,
pCC
!
pꢀCC
=
16.54 kJ molꢁ1
, respectively. From Table 5, it is clear that
nOðNÞ ! rꢀCO and nOðNÞ ! rCꢀC interactions gives more stabilisation
than that of the bond pair donor orbital. As well, pCC
!
pꢀCC pꢀCO
=
interaction between the ring CAC bond pair and the CAC/CAO
antibonding orbital gives more stabilisation energy.
Vibrational assignment and analysis
The FTIR and FT-Raman spectra of the compounds 4ABH and
4HBH are shown in Figs. 12 and 13. The experimental and
theoretical frequencies computed by B3LYP method with

Table 7
The Experimental FTIR and FT-Raman frequencies, calculated frequencies, force field along with their relative intensities, probable assignments and potential energy distribution (PED) of 4-aminobenzohydrazide.a
Observed
B3LYP/6-311++G(d,p) Calculated
wavenumber
B3LYP/6-31G(d,p) Calculated wavenumber
B3LYP/aug-cc-pVDZ Calculated
wavenumber
Depolarisation
ratio
%PED
wavenumber
(cmꢁ1
FTIR
)
FTR
Unscaled
Scaled
IR
Unscaled
Scaled
IR
Raman
intensity
Unscaled
Scaled
IR
(cmꢁ1
)
(cmꢁ1
)
intensity
(cmꢁ1
)
(cmꢁ1
)
intensity
(cmꢁ1
)
(cmꢁ1
)
intensity
3428 s
3349 s
3307 s
3276 s
3682
3593
3581
3557
3490
3196
3177
3159
3424
3341
3295
3272
3211
3068
3050
3033
21.31
7.21
38.42
25.02
1.67
2.61
11.10
16.39
3692
3585
3582
3540
3473
3217
3194
3176
3434
3334
3331
3292
3230
3088
3066
3049
14.16
1.07
28.75
17.62
6.42
2.64
14.40
19.67
0.314
0.469
1.000
0.301
0.987
0.333
0.421
0.357
3676
3577
3567
3549
3467
3207
3187
3168
3419
3327
3317
3265
3224
3079
3060
3041
20.08
6.21
35.76
24.55
2.10
2.55
10.27
17.68
0.75
0.66
0.18
0.14
0.16
0.21
0.17
0.35
92m
90m
95m
89m
94m
96m
91m
95m
aNH2
aNH2
NH
sNH2
sNH2
CH
3310 w
3235 vs 3234 w
3058 w
3035
vw
3056 w
CH
CH
3157
1758
1682
3031
1617
1632
1614
1598
1560
1501
1470
14.99
291.42
14.80
254.59
81.35
6.11
3173
1795
1688
1678
1659
1623
1562
1520
3046
1616
1620
1611
1593
1558
1500
1459
16.50
229.78
7.39
283.43
9.52
4.89
17.18
151.54
0.287
0.308
0.078
0.581
0.136
0.013
0.114
0.124
3166
1746
1663
1658
1638
1611
1544
1510
3039
1606
1613
1608
1589
1563
1498
1465
13.15
260.36
8.19
325.38
5.33
6.44
21.57
137.68
0.54
0.22
0.63
0.44
0.50
0.27
0.42
0.33
92
97
90
87dNH2
89dNH2
85
87
82bNH
m
m
m
CH
C@O
CC
1622 vs
1605 vs 1599 vs 1664
1564 m 1564 m 1647
1543 s
1505 vs 1509 w
1441 w
1608
1547
1515
m
m
CC
CC
23.71
132.38
1458
vw
1462
1358
1338 m 1332
1314
1418
1317
1292
1275
1273
1237
1.06
1.38
6.47
6.22
57.53
265.42
1476
1375
1340
1329
1325
1286
1417
1320
1286
1276
1272
1235
0.52
4.08
11.89
55.24
2.22
0.002
0.003
0.009
0.020
0.036
0.295
1459
1368
1325
1311
1309
1281
1415
1327
1285
1272
1270
1243
0.87
3.18
9.64
1.25
71.53
244.88
0.43
0.42
0.30
0.11
0.65
0.24
90m
94m
93m
85m
87m
83m
CC
CN
CN
CC
CC
CC
1363 s
1345 s
1322 vs
1308 s
1203
vw
1312
1275
243.61
1192
vw
1174
vw
1195 m 1216
1180
1156
11.16
74.97
1224
1198
1175
1150
11.33
57.50
0.035
0.112
1213
1187
1177
1151
6.96
0.65
0.18
75bCH + 12bCCC
71 NN + 14bNAH
1164 w
1192
67.99
m
1119 w
1151
1077
1043
1021
984
956
921
850
839
823
778
753
705
653
626
531
526
493
466
421
386
1116
1045
1012
990
954
927
893
825
814
798
755
730
684
633
607
515
510
478
452
408
374
11.83
0.56
37.38
15.37
1.09
1156
1086
1053
1023
981
954
934
850
845
827
790
766
702
654
630
551
542
509
472
422
387
1110
1043
1011
982
942
916
897
816
811
794
758
735
674
628
605
529
520
489
453
405
372
12.29
0.32
31.20
9.12
1.15
5.70
33.08
36.35
9.93
0.010
0.005
0.021
0.002
0.006
0.009
0.080
0.033
0.084
0.023
0.011
0.006
0.002
0.024
0.006
0.024
0.019
0.042
0.008
0.002
0.001
1144
1074
1044
1014
985
954
923
849
840
819
781
763
704
648
624
531
519
482
459
421
384
1110
1042
1013
984
955
925
895
824
815
794
758
740
683
629
605
515
503
468
445
408
372
11.13
0.60
37.71
9.65
0.87
2.50
34.49
37.29
9.69
0.57
0.75
0.54
0.46
0.61
0.45
0.09
0.18
0.18
0.69
0.71
0.65
0.61
0.75
0.56
0.63
0.63
0.62
0.49
0.53
0.75
65bCH + 16bCCC
61bCH + 12bCCC
63bCH + 15bCCC
965 m
956 m
941 w
884 w
843 s
971vw
895 m
781vw
650 w
59
51
56
49
52
c
c
c
q
q
CH + 12
CH + 16
CH + 19
NH2 + 25bCCC
NH2 + 27bNH
c
c
c
CCC
CCC
CCC
3.26
32.85
38.35
7.60
41bCCC + 24bCH
40 CH + 26bCN
45bCCC + 28bCH
41 NH + 17 NN
52bC@O + 14bNH
777 w
3.69
4.41
3.37
c
23.22
101.60
18.17
0.28
15.66
30.42
59.36
281.24
83.02
0.97
69.63
52.12
9.03
27.19
71.98
19.39
0.18
15.69
18.92
56.89
164.82
187.25
1.42
715 w
653 m
639 m
620 m
517 m
c
c
0.38
46
47
x
x
NH2 + 26
NH2 + 24
c
c
CCC
NH
13.35
79.34
135.44
272.97
30.76
0.83
42bCCC + 21bCH
43bCCC + 18bCH
46bCC + 19bC@O
51bCN + 15bNH
495 vw
353 vw
49
46
c
c
C@O + 20
cNH
1.75
2.06
2.39
CN + 22 CCC
c
(continued on next page)

112
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
6-311++Gꢀꢀ, 6-31Gꢀꢀ and aug-cc-pVDZ basis sets along with their
relative intensities, probable assignments and potential energy dis-
tribution (PED) of 4ABH and 4HBH are summarised in Tables 6 and
7, respectively.
CAH vibrations
The aromatic CAH stretching vibrations lie in the range
3100A3000 cmꢁ1 [55]. The CAH stretching vibrations of 4ABH
are seen in IR spectrum at 3058 and 3035 cmꢁ1 while in 4HBH
the bands are observed at 3081(Raman) and 3012 (IR) cmꢁ1. The
potential energy (PED) contribution of the aromatic stretching
modes indicates that these are also highly pure modes like the car-
bon–carbon stretching fundamentals. In accordance with the
bending vibrations of benzene [56] the peaks seen at 1090,
1049 cmꢁ1 (IR) and 1046 cmꢁ1 (Raman) in 4HBH spectra are attrib-
uted to the CAH in-plane bending vibrations. The bands observed
at 1192, 1119 cmꢁ1 (IR) and 1195 cmꢁ1 (Raman) in the spectra of
4ABH are assigned to the CAH in-plane bending vibrations. The
ring CAH out of plane bending vibrations of 4HBH are seen in
the infrared spectrum at 965, 956, 941 and 777 cmꢁ1 whereas in
4ABH the same vibrations are seen at 899, 824 and 774 cmꢁ1 in Ra-
man spectrum. The PED contributions reveals that the CAH in-
plane and out of plane bending vibrations have substantial over-
lapping with the ring CACAC in-plane and out of plane bending
modes, respectively [57].
Carbon vibrations
The aromatic ring carbon–carbon stretching modes of benzene
and its derivatives are noticed in the range 1650–1200 cmꢁ1
[56,58]. Strong to medium lines observed in the IR spectrum of
4HBH at 1591, 1539, 1512, 1467, 1340 and 1282 cmꢁ1 are ascribed
to the CAC stretching modes. The CAC stretching modes of 4ABH
are observed as very strong to weak lines in the IR spectrum at
1543, 1505, 1322, 1308 and 1203 cmꢁ1. With reference to vibra-
tional modes of benzene [56] the CACAC in-plane bending and
out of plane bending modes are assigned. The lines identified at
517 (IR) and 495 cmꢁ1 (Raman) are assigned to CACAC in-plane
bending vibrations of 4ABH and
a strong line identified at
116 cmꢁ1 in Raman is assigned to CACAC out of plane bending
vibration. The CACAC in-plane and out of plane bending modes
of 4HBH are seen at 768 cmꢁ1 in IR and 359 cmꢁ1 in Raman,
respectively. In 4HBH spectra CAC in-plane and out of plane bend-
ing modes are found at 525, 487 (IR) and 126 (Raman) cmꢁ1
.
C@O, CAO and OAH vibrations
The carbonyl C@O stretching modes are reported in the region
1750–1650 cmꢁ1 [38]. The carbonyl stretching frequency is ob-
served at 1622 cmꢁ1 in IR spectrum of 4HBH and 4ABH. The low
frequency of C@O stretching is due to the nitrogen lone pair elec-
tron being delocalized towards the carbonyl end and the electron
donating nature of the hydroxyl and amino substituents [38]. The
C@O in-plane bending mode of 4ABH is assigned to the wavenum-
ber 653 cmꢁ1 in the infrared and at 650 cmꢁ1 in Raman spectra. In
4HBH, the same has been calculated with B3LYP/6-311++Gꢀꢀ meth-
od is 671 cmꢁ1. As expected the CAO stretching mode of 4HBH is
identified at 1140 cmꢁ1 in the IR and at 1152 cmꢁ1 in Raman spec-
tra. The stretching frequency of OAH in 4HBH is identified at
3428 cmꢁ1 in IR spectrum. The OAH in-plane bending mode of
4HBH is identified at 1257 cmꢁ1 in the IR and at 1255 cmꢁ1 in Ra-
man spectra whereas the out of plane bending mode is identified at
631 cmꢁ1 in the IR and at 641 cmꢁ1 in Raman spectra.

V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
113
Table 8
Frequency correlation of 4-hydroxybenzohydrazide and 4-aminobenzohydrazide with benzohydrazide vibrations.a
Molecule
m
aNH2
m
NH
m
sNH2
m
C@O
dNH2
m
CN
m
NN
cNH
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
4HBH
4ABH
BHa
3320 vs
3349 s
3300 s
3314
3341
3315
3280 m
3307 s
3291 s
3274
3295
3275
3202 m
3235 vs
3213 s
3227
3211
3230
1622 vs
1622 vs
1661 s
1634
1617
1672
1607 s
1605 vs
1616 vs
1638
1614
1638
1329 m
1345 s
1361 s
1321
1292
1345
1175 vs
1174 vw
1165 m
1164
1156
1169
652 m
715 w
675 s
647
730
650
a
BH = benzohydrazide [38]; 4HBH = 4-hydroxybenzohydrazide; 4ABH = 4-aminobenzohydrazide; A = Experimental values; B = Theoretical (B3LYP/6-311++Gꢀꢀ) values.
in Fig. 14. The C@O stretching, CAN stretching and ANH2 deforma-
tions of 4ABH and 4HBH are observed in the lower wavenumber
region than that of benzohydrazide. This is due to the electron
donating nature of AOH and ANH2 groups which in turn induce
the delocalization of the p-electrons towards the C@O group. The
asymmetric (3349 cmꢁ1) and symmetric (3235 cmꢁ1) ANH2 vibra-
tions of 4ABH is observed in the higher wavenumber than in ben-
zohydrazide (3300 and 3213 cmꢁ1). In the case of 4HBH the
asymmetric stretching vibration is 20 cmꢁ1 more than that of ben-
zohydrazide while the symmetric stretching is 11 cmꢁ1 less than in
benzohydrazide. The higher ANH2 stretching wavenumber is due
to the electron donating nature of the amino group. A blue shift
is observed in the NAH stretching of 4ABH than in benzohydrazide.
The substituent effect is negligible on the NAN stretching fre-
quency and is well correlated with the corresponding mode of
benzohydrazide.
Fig. 14. Correlation of some important fundamental modes of benzohydrazide,
4-aminobenzohydrazide (4ABH) and 4-hydroxybenzohydrazide (4HBH).
Conclusion
Experimental and theoretical vibrational spectroscopic studies
and DFT calculations of 4-hydroxybenzohydrazide and 4-amin-
obenzohydrazide using FTIR and FT-Raman spectral data have
been presented in this investigation. A comparative study on
the equilibrium geometries, structural parameters and harmonic
frequencies of title molecules were provided at DFT level of the-
ory utilising 6-31Gꢀꢀ, 6-311++Gꢀꢀ and aug-cc-pVDZ basis sets. In
4ABH the mean planes of the benzene ring and the planar
hydrazide group are inclined at 28.6 with respect to each other.
But the mean planes of the benzene ring and the planar hydra-
zide group of 4HBH are inclined at 24.5 with respect to each
other.
The most stable conformer of 4HBH is more stable by
12.47 kcal molꢁ1 than the stable conformer of 4ABH. Except hydra-
zide hydrogens, the 4ABH and 4HBH molecules are essentially pla-
nar as evidenced by the C6AC1AC7AO8, N10AN9AC7AC1 and
N10AN9AC7AO8 torsion angles of ꢁ22.6°, ꢁ178.8° and 1.0° for
4ABH while these are ꢁ23.3°, ꢁ23.2° and 158.5°, respectively.
The heat capacity, entropy and enthalpy change of 4-amin-
obenzohydrazide (4ABH) is found to be more than in 4-hydrox-
ybenzohydrazide (4HBH) in the range 50–700 °C.
ANH and ANH2 vibrations
The bands of very strong to medium intensity observed at 3320
and 3213 cmꢁ1 in the infrared spectrum are assigned to the ANH2
asymmetric and symmetric stretching modes of 4HBH, respec-
tively. Contrasting, the bands due ANH2 stretching vibrations in
4ABH exists at higher wavenumbers with deviations in the range
30–100 cmꢁ1. The ANH2 asymmetric stretching vibration of hydra-
zide group in 4ABH appears at 3349 cmꢁ1 in IR and at 3310 cmꢁ1 in
Raman spectra while the symmetric stretching is observed at
3235 cmꢁ1 in IR and at 3310 cmꢁ1 in Raman. The amino group
stretching (ANH2) in 4ABH are dwell in slightly higher wavenum-
ber than that of hydrazide ANH2 bands. Strong band at 3428 cmꢁ1
in IR is due to asymmetric stretching vibration of the amino group
while the band at 3276 cmꢁ1 in IR is due to symmetric stretching.
In 4ABH, ANH2 deformation mode of hydrazide group is identified
at 1605 cmꢁ1 in IR and at 1599 cmꢁ1 in Raman spectra while a red
shift is observed in the deformation mode of amino group and is
seen in at 1564 cmꢁ1 in IR spectrum. Strong bands in IR at
1607 cmꢁ1 and at 1612 cmꢁ1 in Raman are assigned to the ANH2
deformation mode of 4HBH. The NAH stretching vibration of
hydrazide group in 4HBH appears at 3280 cmꢁ1 in IR and at
3256 cmꢁ1 in Raman spectra whereas a blue shift is observed in
4ABH molecule and the corresponding band is found at
3307 cmꢁ1. The other fundamental modes of 4HBH and 4ABH are
also assigned in accordance with literature [38] and are presented
in Tables 6 and 7.
The frontier orbital energy gaps Eg = ELUMO ꢁ EHOMO in case of
4HBH and 4ABH is found to be 0.1969 and 0.1875 a.u., respectively.
The MEP reveals that the maximum values of positive and negative
potentials of 4ABH are 0.0835e and ꢁ0.1055e, respectively while
0.1149e and ꢁ0.1028e for 4HBH.
The C@O stretching, CAN stretching and ANH2 deformations of
4ABH and 4HBH are observed in the lower wavenumber region
than that of benzohydrazide. This is due to the electron donating
nature of AOH and ANH2 groups which in turn induce the delocal-
Frequency correlation
ization of the
p-electrons towards the C@O group. A blue shift is
In order to explain the substituents effects on the fundamental
frequencies, some important fundamental modes of 4ABH and
4HBH are correlated with the parent benzohydrazide modes and
are presented in Table 8. These effects are pictorially illustrated
observed in the NAH stretching of 4ABH than in benzohydrazide.
The substituent effect is negligible on the NAN stretching fre-
quency and is well correlated with the corresponding mode of
benzohydrazide.

114
V. Arjunan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 100–114
[36] Mohammad Ali Kamyabi, S. Shahabi, H. Hosseini–Monfared, J. Chem. Eng. Data
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