Density functional theory study, FT-iR and FT-Raman spectra and SQM force field calculation for vibrational analysis of 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one

Article abstract of DOI:10.1016/j.saa.2013.05.003

FT-iR and FT-Raman spectra of 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one were recorded and analyzed in the solid phase. The optimized molecular geometry and vibrational wavenumbers have also been calculated in optimized structure by using DFT method. S

Full text of DOI:10.1016/j.saa.2013.05.003

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Density functional theory study, FT-IR and FT-Raman spectra and SQM
force field calculation for vibrational analysis of 1, 3-Bis (hydroxymethyl)
benzimidazolin-2-one
b
c
d
Lynnette Joseph a,d, D. Sajan a, , K. Chaitanya , H.C. Devarajegowda , Jayakumary Isac
⇑
a Department of Physics, Bishop Moore College, Mavelikara, Alappuzha 690 110, Kerala, India
b Department of Chemistry, Nanjing University of Science and Technology, Xialingwei 200, Nanjing, People’s Republic of China
c Department of Physics, Yuvaraja’s College (Constituent College), University of Mysore, Mysore 570 005, Karnataka, India
d Department of Physics, C.M.S College, Kottayam 686 001, Kerala, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Complete analysis of vibrational
spectra and DFT investigations
performed.
ꢀ
ꢀ
ꢀ
Molecular structure of the compound
is studied using DFT method.
The NBO analysis reveals the
hyperconjugative interactions.
The electrostatic potential has been
studied for predicting active sites.
a r t i c l e i n f o
a b s t r a c t
Article history:
FT-IR and FT-Raman spectra of 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one were recorded and ana-
lyzed in the solid phase. The optimized molecular geometry and vibrational wavenumbers have also
been calculated in optimized structure by using DFT method. Scaled quantum mechanical force fields
have also been used to calculate potential energy distributions in order to make conspicuous vibrational
assignments. The red shifting of the OAH stretching wavenumber is due to the formation of OAHꢁ ꢁ ꢁO
intermolecular hydrogen bonding. The lowering and splitting of the carbonyl stretching vibrational
modes is assigned to the intermolecular association based on C@Oꢁ ꢁ ꢁH type hydrogen bonding in the
molecule. Chemical interpretation of hyperconjugative interactions was done by natural bond orbital
analysis.
Received 31 January 2013
Received in revised form 30 April 2013
Accepted 2 May 2013
Available online 14 May 2013
Keywords:
Vibrational spectra
DFT calculation
SQMFF and NBO analysis
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
antiparasitic, antimicrobial [4], antiviral [5], anticancer [6,7],
anti-inflammatory [8] and anti-diabetic [9] agents. They also play
Benzimidazole [1–3] and its derivatives are important heterocy-
clic compounds which have attracted great attention due to their
biological and pharmaceutical activities. They are reported as
very important role in the synthesis of many natural products
and synthetic drugs. Compounds possessing the benzimidazole
unit express significant activity against several viruses such as
HIV [10,11], Herpes (HSV-1) [12], human cytomegalovirus (HCMV)
and influenza. 1, 3-Bishydroxyalkylated benzimidazolones are an
important class of functionalized benzimidazoles which have been
found to be useful as polymer intermediates [13], fire retardants,
⇑
Corresponding author. Tel.: +91 9495043765; fax: +91 4792303230.
E-mail addresses: dsajand@gmail.com, dsajanbmc@gmail.com, drsajanbmc@
gmail.com (D. Sajan).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.05.003

L. Joseph et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440
433
and in curing process in textile industry [14]. Solid state chemistry
of hydroxy methylated benzimidazole derivatives leading to ther-
mal extrusion of formaldehyde have been reported [15].
employed to calculate optimized bond lengths, bond angles, dihe-
dral angles, atomic charges, vibrational wavenumbers with their IR
intensities and Raman scattering activities. All these calculations
were performed using Gaussian 09 program [30]. The optimized
geometry corresponding to the minimum on the potential energy
surface has been obtained by solving the self-consistent field
(SCF) equation iteratively. Harmonic vibrational wavenumbers
have been calculated using analytic second derivatives to confirm
the convergence to minima on the potential surface and to evalu-
ate the zero-point vibrational energies without imposing any
molecular symmetry constraints. It is a well-known fact that ab in-
tio calculations tend to overestimate the vibrational wavenumbers
with respect to the experimental ones [31–33]. This is due to sev-
eral reasons, for instance, the use of finite basis set, the incomplete
implementation of the electronic correlation and the neglect of
anharmonicity effects in the theoretical treatment. However, the
calculated ab initio force field can be improved by using the scaled
quantum mechanical force field (SQMFF) methodology. For subse-
quent normal coordinate analysis (NCA), the force field obtained in
cartesian coordinates and dipole derivatives with respect to atomic
displacements were extracted from the archive section of the G09
output and transformed to a suitably defined set of internal coor-
dinates (the ‘‘natural coordinates’’) which are collected in Table 1
by means of a modified version of the MOLVIB program [34].
The modifications introduced by Sundius [34] allow least squares
refinement of multiple scale factors of the QM force field and calcu-
lation of the normal modes, potential energy distribution (PED),
transition moment vectors and IR intensities with the scaled force
field. The prediction of Raman intensities was carried out by follow-
ing the procedure outlined below. The Raman activities (Si) calcu-
lated by Gaussian 09 and adjusted during scaling procedure with
MOLVIB were converted to relative Raman intensity (Ii) using the
following relation from the basic theory of Raman scattering [35,36]
The infrared and Raman spectra of benzimidazole derivatives
have been reported by several authors [16–20]. Recently density
functional theory (DFT) has emerged as a powerful tool for analyz-
ing vibrational spectra of fairly large molecules. The application of
DFT to chemical systems has received much attention because of
faster convergence in time than traditional quantum mechanical
correlation methods [21–24]. In this paper, we report for the first
time the detailed vibrational spectral investigation of 1, 3-Bis
(hydroxymethyl) benzimidazolin-2-one (Fig. 1) using scaled quan-
tum mechanical (SQM) force field technique based on density func-
tional theory (DFT) calculations. The experimental and theoretical
results supported each other and the calculations are valuable for
providing a reliable insight into the vibrational spectra and molec-
ular properties.
Experimental procedure
The title compound was prepared by following a literature
method [25]. A mixture of 2-hydroxy benzimidazole (13.4 g,
0.01 M) and 37% formalin (30 ml, 1 M) was refluxed for 30 min in
presence of 100 ml water. The solid product formed was filtered
and single crystals were grown by slow evaporation in water (yield
92%, m.p. 433 K).
FT-IR spectrum of the synthesized material was recorded in the
wavenumber range 400–4000 cmꢂ1 by KBr pellet technique (Ther-
mo Nicolet AVATAR 370 DTGS FT-IR spectrophotometer). The data
were collected at 1 cmꢂ1 resolution and the spectrum was en-
hanced by the accumulation of 200 scans. The Raman spectrum
of the solid compound was recorded between 3600 and 50 cmꢂ1
with a Bruker RF100/S spectrometer equipped with an Nd:YAG la-
ser (excitation line of 1064 nm, 800 mW of laser power) and a Ge
detector cooled to liquid nitrogen temperature. The spectrum
was recorded with a resolution of 1 cmꢂ1 and 200 scans.
4
fðmo
mi 1 ꢂ exp
ꢂ
miÞ Si
ꢀ
h
ꢁi
Ii ¼
ð1Þ
ꢂhcmi
kT
where mo is the exciting frequency (in cmꢂ1 units), mi is the vibra-
tional wavenumber 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.
Computational details
Density Functional Theory (DFT) [26] with the hybrid function-
als (B3LYP) [27–29] with the 6-311++G(d,p) basis set have been
The natural bonding orbitals (NBO) calculations [37] were per-
formed using NBO 5.1 program as implemented in the Gaussian 09
package at the DFT/B3LYP level in order to understand various sec-
ond order interactions between the filled orbitals of one subsystem
and vacant orbitals of another subsystem, which is a measure of
the intermolecular delocalization or hyperconjugation. The hyper-
conjugative interaction energy was deduced from the second-order
perturbation approach [38]
h
r
ꢃ
jFj
r
ꢂ
i
Fij2
2
Eð2Þ ¼ ꢂn
¼ ꢂnr
DE
ð2Þ
r er
er
2
2
where h
r
|F|
r
i or Fij is the Fock matrix element between the i and j
r
and r⁄ NBOs, and n
r
ꢃ
NBO orbitals, e and er are the energies of
r
is the population of the donor
r orbital.
Crystal structure
The 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one (BHMB)
molecule crystallizes in space group C2/c. From the single crystal
X-ray Diffraction data [39], the crystal belongs to monoclinic sys-
tem with the following cell dimensions: a = 13.5515(14) Å,
b = 11.0848(12) Å, c = 17.6253(19) Å, b = 94.216°, Z = 12. The
asymmetric unit of the title compound contains one and a half
Fig. 1. Molecular structure and atomic numbering of 1, 3-Bis (hydroxymethyl)
benzimidazolin-2-one.

434
L. Joseph et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440
Table 1
Optimized geometric parameters of 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one.
Bond lengths (Å)
6-311++ G(d,p)
X-ray [39]
Bond angles (°)
6-311++ G(d,p)
X-ray [39]
Dihedral angles (°)
6-311++ G(d,p)
X-ray [39]
C1AC2
C1AC6
C1AN13
C2AC3
C2AN12
C3AC4
C3AH8
C4AC5
C4AH9
C5AC6
C5AH10
C6AH11
C7AN12
C7AN13
C7AO14
1.406
1.386
1.399
1.386
1.399
1.399
1.083
1.396
1.083
1.399
1.083
1.083
1.394
1.394
1.220
1.447
1.447
1.092
1.090
1.413
1.090
1.413
1.092
0.964
0.964
1.393
1.384
1.399
1.384
1.399
1.387
0.929
1.387
0.930
1.389
0.930
0.929
1.376
1.371
1.237
1.446
1.446
0.970
0.970
1.406
0.970
1.406
0.970
0.820
0.820
C2AC1AC6
C2AC1AN13
C1AC2AC3
C1AC2AN12
C6AC1AN13
C1AC6AC5
C1AC6AH11
C1AN13AC7
C1AN13AC15
C3AC2AN12
C2AC3AC4
C2AC3AH8
C2AN12AC7
C2AN12AC18
C4AC3AH8
C3AC4AC5
C3AC4AH9
C5AC4AH9
C4AC5AC6
C4AC5AH10
C6AC5AH10
C5AC6AH11
121.3
107.0
121.3
107.0
131.7
117.5
121.5
110.0
127.6
131.7
117.5
121.5
110.0
127.6
121.0
121.2
119.2
119.6
121.2
119.6
119.2
121.0
106.0
127.0
122.4
127.0
122.4
108.8
113.7
106.6
106.6
108.8
113.7
109.9
111.8
106.1
108.7
121.59
106.87
121.59
106.87
131.53
116.74
121.60
109.56
125.56
131.53
116.74
121.60
109.56
125.56
121.66
121.66
119.17
119.17
121.66
119.17
119.17
121.66
107.14
126.43
124.00
126.43
124.00
127.14
112.83
109.24
109.24
109.25
111.86
107.98
109.2
C1AC2AC3AC4
C2AC3AC4AC5
C3AC4AC5AC6
C4AC5AC6AC1
C5AC6AC1AC2
C6AC1AC2AC3
C3AC2AC1AN13
C4AC3AC2AN12
C2AC1AC6AH11
C1AC6AC5AH10
C6AC5AC4AH9
C5AC4AC3AH8
H8AC3AC2AN12
H8AC3AC4AH9
H9AC4AC5AH10
0.8
ꢂ0.1
1.5
0.1
ꢂ0.2
ꢂ1.5
ꢂ0.1
1.1
0.8
0.5
ꢂ1.3
178.4
ꢂ178.8
ꢂ178.3
ꢂ179.9
179.5
179.1
1.9
ꢂ1.9
177.9
179.7
ꢂ179.4
178.7
178.4
179.8
ꢂ0.1
0.1
ꢂ0.7
ꢂ0.5
ꢂ1.5
N
N
12AC18
13AC15
H
H
10AC5AC6AH11
11AC6AC1AN13
ꢂ0.7
1.2
1.9
0.7
1.3
C
C
C
C
C
C
15AH16
15AH17
15AO20
18AH19
18AO22
18AH24
C1AC2AN12AC7
C2AN12AC7AN13
C1AN13AC7AN12
C2AC1AN13AC7
1.4
ꢂ0.5
ꢂ1.5
ꢂ0.5
1.1
1.4
ꢂ0.2
ꢂ0.6
179.8
ꢂ178.7
178.3
177.5
165.5
47.5
N
12AC2AC1AN13
ꢂ1.7
179.4
179.4
179.4
179.4
156.4
37.9
N
N
12AC7AN13
12AC7AO14
C2AC1AN13AC15
C1AN13AC7AO14
C2AN12AC7AO14
C1AC2AN12AC18
C2AN12AC18AH24
C2AN12AC18AH19
O
O
20AH21
22AH23
C7AN12AC18
13AC7AO14
C7AN13AC15
N
N12AC18AH19
N12AC18AO22
N12AC18AH24
N13AC15AH16
N13AC15AH17
N13AC15AO20
H16AC15AH17
H16AC15AO20
H17AC15AO20
N
O
12AC18AO22AH23
14AC7AN12AC18
ꢂ72.3
93.4
1.3
ꢂ2.7
C7AN12AC18AH24
C7AN12AC18AH19
C7AN13AC15AH16
C7AN13AC15AH17
C1AN13AC15AH16
C1AN13AC15AH17
ꢂ25.8
ꢂ144.2
ꢂ25.7
ꢂ144.2
156.5
38.0
15.7
133.6
32.9
150.4
ꢂ147.0
ꢂ29.6
ꢂ90.5
109.23
109.51
C
15AO20AH21
N
13AC15AO20AH21
ꢂ72.3
molecules, one lying on a general position and the other on a two-
fold rotation axis (Fig. 1). Atoms O14 and C7 are found on the two-
fold rotation axis. The two independent benzimidazole ring
systems form a dihedral angle of 18.96 (5)°. There are no intramo-
lecular hydrogen bonding between N-hydroxymethyl and carbonyl
groups. In the crystal, OAHꢁꢁꢁO hydrogen bonding involving N-
hydroxymethyl and carbonyl groups results in the formation of a
three-dimensional network (Fig. S1).
attachment of the imidazole moiety to the benzene ring in the
place of hydrogen atoms. The breakdown of hexagonal symmetry
of the benzene ring is obvious from the elongation of C1AC2
(1.393 Å) from the remaining C2AC3, C3AC4, C4AC5, C5AC6 and
C1AC6 bond lengths. DFT calculation indicates shortening of the
endocyclic angles C1AC6AC5, C2AC3AC4 by 2.5° increase in the an-
gle C2AC1AC6, C1AC2AC3, C3AC4AC5 and C4AC5AC6 by 1.3°, 1.3°,
1.2° and 1.2°, respectively associated with the charge-transfer
interaction from N13 and N12 to the ring system. Owing to the
low scattering factors of hydrogen atoms in X-ray diffraction, the
experimental bond lengths of XAH bonds are expected to be short-
er than the estimated bond lengths [40].
Geometry optimization
The calculated molecular structure of BHMB was constructed
based on its crystallographic data and the obtained optimized
geometry was checked as minima on the potential energy surfaces
by wavenumber calculations. The global energy minimum ob-
tained by DFT of the structure optimization for the title compound
Natural bond orbital analysis
NBO analysis provides the most accurate possible ‘natural Lewis
structure’ picture of orbits, because all orbital details are mathe-
matically chosen to include the highest possible percentage of
the electron density. A useful aspect of the NBO method is that it
gives information about interactions in both filled and virtual orbi-
tal spaces that could enhance the analysis of intra- and inter-
molecular interactions. The second order Fock matrix was carried
out to evaluate the donor–acceptor interactions in the NBO analy-
sis [41]. The interactions result is a loss of occupancy from the
localized NBO of the idealized Lewis structure into an empty
non-Lewis orbital. Delocalization of electron density between
occupied Lewis type (bond or lone pair) NBO orbitals and formally
unoccupied (antibond or Rydberg) non-Lewis NBO orbitals
was ꢂ3.517 ꢄ 106 kJ/molꢂ1
. The experimental and optimized
structural parameters of BHMB calculated at the B3LYP level of
theory with a 6-311++G(d,p) basis set are listed in Table 1 in accor-
dance with the atom numbering given in Fig. 1. Most of the opti-
mized bond lengths are slightly longer than the experimental
values agreeing within 0.001–0.122 Å except the C7@O14
(0.017 Å) bond length. This discrepancy may be justified on the ba-
sis that the calculations were performed on a single molecule in
the gaseous state contrary to the experimental values, which were
recorded in presence of intermolecular interactions. As found
experimentally, the phenyl ring appears little distorted and the an-
gles are slightly out of perfect hexagonal structure. It is due to the

L. Joseph et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440
435
corresponds to a stabilizing donor–acceptor interaction. In NBO
HOMO and LUMO analyses
analysis large E(2) value shows the intensive interaction between
electron-donors and electron-acceptors and greater the extent of
conjugation of the whole system, the possible intensive interac-
tions are given in Table 2. The second-order perturbation theory
analysis of Fock matrix in NBO basis shows strong intramolecular
hyperconjugative interactions of electrons. The hyperconjugative
Highest occupied molecular orbital (HOMO) and lowest unoc-
cupied molecular orbital (LUMO) are very important parameters
for quantum chemistry. We can determine the way the molecule
interacts with other species; thus, they are called the frontier orbi-
tals. HOMO, which can be thought the outermost orbital containing
electrons, tends to give these electrons such as an electron donor.
On the other hand, LUMO can be thought as the innermost orbital
containing free places to accept electrons [42]. Owing to the inter-
action between HOMO and LUMO orbital of a structure, transition
interactions are formed by the orbital overlap between
p(CAC)
bond orbital to pꢃ(CAC) antibonding orbital, which results in ICT
(intra molecular charge transfer) causing stabilization of the sys-
tem. These interactions can be identified by finding the increase
in electron density (ED) in anti-bonding orbital. The stabilization
energy E(2) associated with hyperconjugative interactions
n1(N12) ? rꢃ (C7AO14), n2(N12) ? rꢃ (C2AC3) and n1(N13) ? rꢃ
state transition of p–
pꢃ type is observed with regard to the molec-
ular orbital theory [43,44]. Therefore, while the energy of the
HOMO is directly related to the ionization potential, LUMO energy
is directly related to the electron affinity. Energy difference be-
tween HOMO and LUMO orbital is called as energy gap that is an
important stability for structures [44]. 3D plots of highest occupied
molecular orbitals (HOMOs) and lowest unoccupied molecular
orbitals (LUMOs) with the energy values are presented in Fig. 2.
The HOMO and LUMO orbitals are distributed not only on the con-
jugated molecular backbones, but also on substituent. The HOMO
and LUMO energy are ꢂ6.018 eV and ꢂ5.124 eV at the DFT level.
(C7AO14), n2(N13) ? rꢃ (C1AC6)are obtained as 241.06 kJ molꢂ1
,
158.18 kJ molꢂ1, 241.06 kJ molꢂ1, 158.18 kJ molꢂ1 respectively (Ta-
ble 3) which quantify the extend of intrarmolecular charge trans-
fer. The contributions of the stabilization energies for the
n2(O20) ? rꢃ (N13AC15) [49.267 kJ molꢂ1], n2(O22) ? rꢃ (N12AC18
)
[49.267 kJ molꢂ1], n2(O14) ? rꢃ (C27AN12
)
[108.87 kJ molꢂ1],
n2(O14) ? rꢃ (C27AN13) [108.87 kJ molꢂ1], n1(N12) ? rꢃ (C18AO22
)
]
[52.281 kJ molꢂ1], and n1(N13) ? rꢃ (C15AO20) [52.281 kJ molꢂ1
charge transfers have higher values than the other delocalisation.
These ICTs around the rings can induce large NLO activity in the
molecule. This strong ICT is one of the causes for the biological
activity.
As can be seen from Fig. 2, the energy band gap|(DE)| (energy dis-
tribution between HOMO and LUMO) of the most optimized geom-
etry was calculated to be about 0.894 eV at B3LYP/6-311++G(d,p)
level of theory. Moreover the lower value of the HOMO and LUMO
energy gap explains the eventual charge transfer interactions tak-
ing place within the molecule as well as the large stabilization of
LUMO due to the strong electron-accepter ability of the electron
accepter group [45].
Table 2
Second order perturbation theory analysis of Fock matrix in NBO basis.
Donor
Acceptor
E(2)a (kJ molꢂ1
)
E(j) ꢂ E(i)b (a.u.) F(i, j)c (a.u.)
r
r
(C1AC2)
rꢃ (C1AC6)
rꢃ (C2AC3)
rꢃ (N12AC18
rꢃ (N13AC15
rꢃ (C1AC2)
19.0
19.0
20.0
20.0
21.0
11.0
12.0
80.0
81.0
3.8
9.4
16.0
21.0
11.0
12.0
80.0
81.0
1.27
1.27
1.03
1.03
1.26
1.14
1.29
0.29
0.30
1.34
1.38
1.39
1.26
1.14
1.29
0.29
0.30
0.28
0.28
0.29
0.27
0.55
0.29
0.27
0.55
0.29
0.27
0.55
0.29
0.27
0.55
1.1
0.067
0.067
0.063
0.063
0.072
0.050
0.054
0.068
0.068
0.031
0.050
0.065
0.072
0.050
0.054
0.068
0.068
0.065
0.065
0.095
0.113
0.080
0.095
0.113
0.080
0.095
0.113
0.08
Molecular electrostatic potential
)
)
The molecular electrostatic potential (MESP) is widely used as a
reactivity map displaying most probable regions for the electro-
philic attack of charged point-like reagents on organic molecules
[46]. MESP contour map provides a simple way to predict how dif-
ferent geometries could interact. At any given point r(x, y, z) in the
vicinity of a molecule, the interaction energy between the electri-
cal charge generated from the molecule electrons and nuclei and a
positive test charge (a proton) located at V (r) [47]. The molecular
electrostatic potential (MESP) is related to the electronic density
and a very useful descriptor for determining sites for electrophilic
attack and nucleophilic reactions as well as hydrogen-bonding
interactions [48,49]. In Fig. 3, whereas electrophilic attack was pre-
sented by negative (red) regions, nucleophilic reactivity was
shown by the positive (blue) regions of MESP. As seen from
Fig. 3, the red region was mainly localized on the oxygen atoms
(especially O14) whereas the nucleophilic reactivity of the molecule
was mainly localized on the phenyl ring.
(C1AC6)
rꢃ (C1AN13
rꢃ (C5AC6)
pꢃ (C2AC3)
pꢃ (C4AC5)
rꢃ (C1AC2)
rꢃ (C1AC6)
)
p(C1AC6)
r
r
(C1AN13
)
pꢃ (C7AO14
rꢃ (C1AC2)
rꢃ (C2AN12
rꢃ (C3AC4)
pꢃ (C1AC6)
pꢃ (C4AC5)
pꢃ (C1AC6)
pꢃ (C2AC3)
pꢃ (C2AC3)
)
(C2AC3)
)
p
(C2AC3)
(C4AC5)
p
78.0
78.0
LP2 (N12
LP2 (N13
LP1 N12
LP1 N13
)
158.0
241.0
52.0
158.0
241.0
52.0
158.18
241.06
52.28
158.18
241.06
52.28
8.29
108.87
108.87
10.26
49.27
10.26
49.27
rꢃ (C7AO14
)
rꢃ (C18AO22
)
)
pꢃ (C1AC6)
rꢃ (C7AO14
)
rꢃ(C15AO20
)
pꢃ (C2AC3)
rꢃ (C7AO14
)
Vibrational analysis
rꢃ (C18AO22
)
rꢃ (C1AC6)
rꢃ (C7AO14
0.095
0.113
0.08
0.042
0.119
0.119
0.044
0.078
0.044
0.078
A detailed vibrational description can be given by means of nor-
mal coordinate analysis. For this purpose, a full set of standard
internal coordinates were defined as given in Table 3. From these,
a non-redundant set of local symmetry coordinates were con-
structed by suitable linear combinations of internal coordinate’s
following the recommendations of Pulay et al. [50–53] and they
were depicted in Table S1 (Supporting information). The observed
and calculated wavenumbers together with the calculated IR and
Raman intensities and normal mode description (characterized
by PED) are reported in Table 4. For visual comparison, the
observed and simulated FTIR and FT-Raman spectra of the title
)
rꢃ (C15AO20
)
LP1 O14
LP2 O14
rꢃ (C7AN12
rꢃ (C7AN12
rꢃ (C7AN13
)
)
)
0.66
0.66
0.99
0.66
0.99
0.66
LP1 O20
LP2 O20
LP1 O22
LP2 O22
rꢃ (C15AH17
rꢃ (N13AC15
rꢃ (C18AH19
rꢃ (N12AC18
)
)
)
)
a
b
c
E(2) means energy of hyperconjugative interactions; cf. Eq. (2).
Energy difference between donor and acceptor i and j NBO orbitals.
F(i, j) is the Fock matrix element between i and j NBO orbitals.

436
L. Joseph et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440
Table 3
Definition of internal coordinates of 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one.
No. (i)
Symbol
Type
Definitiona
Stretching
1–4
5–8
Ri
Ri
Ri
Ri
Ri
Ri
Ri
Ri
CAH
CH2
C@O
CAC
C3AH8, C4AH9, C5AH10, C6AH11
C15AH16, C15AH17, C18AH19, C18AH24
C7AO14
C1AC2, C2AC3, C3AC4, C4AC5, C5AC6, C6AC1
C1AN13, C7AN13, C7AN12, C2AN12
C18AO22, C15AO20
9
10–15
16–19
20–21
22–23
24–25
CAN
CAO (sub)
CAN(sub)
OAH
C15AN13, C18AN12
O20AH21, O22AH23
In-plane bending
26–33
34–35
36–37
38–41
c
c
c
c
c
i
i
i
i
i
CAH
CAO
NACAO
CAN(sub)
HACAH
C2AC3AH8, C4AC3AH8, C3AC4AH9, C5AC4AH9, C4AC5AH10, C6AC5AH10, C5AC6AH11, C1AC6AH11
N13AC7AO14, N12AC7AO14
N12AC18AO22, N13AC15AO20
C2AN12AC18, C7AN12AC18, C1AN13AC15, C7-N13AC15
H16AC15AH17, H19AC18AH24
42–43
44–47
48–53
54–58
59–60
N13AC15AH16, N13AC15AH17, N12AC18AH19, N12AC18AH24
C1AC2AC3, C3AC4AC5, C5AC6AC1, C2AC3AC4, C4AC5AC6, C6AC1AC2
C1AN13AC7, C2AC1AN13, C7AN12AC2, N12AC2AC1, N13AC7AN12
C15AO20AH21, C18AO22AH23
c
c
i
i
Ring 1
Ring 2
CAOAH
Out-of-plane bending
61–64
65
66–67
q
q
q
i
i
i
CAH
CAO
CAN
H8AC3AC2AC4, H9AC4AC3AC5, H10AC5AC4AC6, H11AC6AC5AC1
O14AC7AN13AN12
C18AN12AC7AC2, C15AN13AC1AC7
Torsion
68–73
74–78
79–82
83–84
85–88
89–90
ti
ti
ti
ti
ti
ti
Ring 1
Ring 2
HCOH
NCOH
CNCH
CCCN
C1AC2AC3AC4, C3AC4AC5AC6, C5AC6AC1AC2, C2AC3AC4AC5, C4AC5AC6AC1, C6AC1AC2AC3
N13AC7AN12AC2, N12AC2AC1AN13, C2AC1AN13AC7, C1AN13AC7AN12, C7AN12AC2AN1
H16AC15AO20AH21, H17AC15AO20AH21, H19AC18AO22AH23, H24AC18AO22AH23
N12AC18AO22AH23, N13AC15AO20AH21
C7AN13AC15AH16, C1AN13AC15AH16, C2AN12AC18AH19, C7AN12AC18AH19
C6AC1AC2AN12, C3AC2AC1AN13
a
For numbering of atom refer Fig. 1.
compound are presented in Figs. 4 and 5, which help to understand
the observed spectral features.
charge distribution and on their effects on infrared intensities. The
methylene group hydrogen atoms in BHMB are simultaneously sub-
jected to the electronic effects of backdonation and hyperconjuga-
tion leading to the blue shifting of stretching wavenumbers and
decrease of infrared intensities, as discussed in the preceded methyl
vibrations section. The methylene asymmetric stretching manifests
their characteristic bands at 2990 cmꢂ1 and 2957 cmꢂ1 in IR as weak
bands and PED calculations predict these modes at 3007 cmꢂ1
(94%). The Raman counterpart is observed at 2990 cmꢂ1 and
2958 cmꢂ1 with medium intensity. The methylene group nearer to
oxygen and nitrogen atom can be correlated to the higher wave-
number band owing to the proximity of the high electronegative
nitrogen and oxygen atom and therefore large negative charges
are backdonated to the methylene groups. Likewise the symmetri-
cal stretching band appear at 2924 cmꢂ1 which is calculated at
2952 cmꢂ1 (94%) and it is inferred that the observed stretching
wavenumbers are blue shifted than the expected wavenumbers
ascertained the existence of electronic effects hyperconjugation
and backdonation due to the blue shifting of stretching wavenum-
bers and the weakening of methylene stretching intensities.
The four bending vibrations of CAH bonds in the methylene
groups are referred as rocking scissoring, twisting and wagging
and they are identified in their respective positions. Methylene
rocking vibration is identified as strong bands in IR at 1489 cmꢂ1
and in Raman at 1488 cmꢂ1 and has 80% of this bending character
vibrations. The scissoring band (dsCH2) in the spectra of hydrocar-
bons occurs at a nearly constant position near 1465 cmꢂ1. This
scissoring mode is characterized by the medium IR band at
1461 cmꢂ1 and a medium Raman band at 1461 cmꢂ1, which is
computed at 1448 cmꢂ1 (78%). The weak band observed in IR at
1279 cmꢂ1 and medium band in Raman at 1281 cmꢂ1 corresponds
to CH2 twisting mode. The in-plane and out-of-plane deformation
modes have also been observed and analyzed supported by PED
calculations.
Hydroxyl vibrational modes
The hydroxyl stretching and bending vibrations can be identi-
fied by the breadth and strength of the band, which are dependent
on the extent of hydrogen bonding. The hydroxyl stretching vibra-
tions are generally observed in the region 3550–3700 cmꢂ1[54–
57]. In IR spectrum the hydroxyl stretching bands splits into two
bands at 3408 cmꢂ1 and 3354 cmꢂ1 corresponding to O20AH21
and O22AH23. The higher position band relates to the OH stretching
mode of the OH-group bound with long H-bond (2.8003 Å), and the
doublet at the lower position relates to the OHA group bound with
the short H-bond (2.7503 Å). The DFT computations give the wave-
number of these bands at 3408 cmꢂ1 with PED 100% for O20AH21
and O22AH23 stretching vibrations. The red shifting of the OAH
stretching wavenumber is due to the formation of OAHꢁ ꢁ ꢁO inter-
molecular hydrogen bonding. The OH in-plane bending vibration
occurs in the general region of 1420–1260 cmꢂ1. The OAH in-plane
bending vibration is observed at 1315 cmꢂ1 as broad band in IR and
strong band at 1315 cmꢂ1 in Raman coupled with CH2 rocking
vibration. The bands at 651 cmꢂ1 and 653 cmꢂ1 in the infrared
and Raman spectrum respectively have been identified as the
OAH torsional mode.
Methylene vibrations
The asymmetrical stretching (mas CH2) and symmetrical stretch-
ing (ms CH2) bands of methylene groups occur near 2940 and
2860 cmꢂ1, respectively [54–57]. The wavenumber of methylene
stretching is increased when the methylene group is part of a
strained ring. The qualitative interpretation of intensities must rely
upon the understanding of some basic aspects of intramolecular

L. Joseph et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440
437
Carbonyl group vibrations
The appearance of strong bands in the FT-IR and weak bands in
the Raman spectra (less polarizability resulting due to highly dipo-
lar carbonyl bond) around 1750–1650 cmꢂ1 in aromatic com-
pounds shows the presence of carbonyl group and is due to the
C@O-stretching motion[58]. The wavenumber of the stretch due
to carbonyl group mainly depends on the bond strength which in
turn depends upon inductive, conjugative, field and steric effects.
Conjugation of carbonyls with double bonds or aromatic rings shift
the band position towards the lower wavenumbers by about
30 cmꢂ1, owing to a redistribution of electrons which weakens
the C@O bond[54–57]. In BHMB carbonyl bonds are conjugated
with aromatic ring, which may increase its single bond character
resulting in lowered values of carbonyl stretching wavenumbers.
In the IR spectra, the carbonyl stretching mode is prominently
splits into two strong bands at 1686 cmꢂ1 and 1665 cmꢂ1. The cor-
responding peaks in the Raman spectra are found to be weak bands
at 1690 cmꢂ1 and 1668 cmꢂ1 due to the less polarizable C@O bond.
The results of computations give the wavenumbers of these modes
to be 1685 cmꢂ1 with PED contribution of 71%. The splitting of the
carbonyl mode may be assigned to Fermi resonance and molecular
association [58–62], which are the reasonable alternatives to ex-
plain the splitting of this mode. However, Fermi resonance may
be excluded by the nature of the intensity ratio of the two compo-
nents. The doublet of the C@O mode band with the traces of crystal
splitting originates from two differently associated CO groups, and
the splitting might be due to intermolecular association based on
C@Oꢁ ꢁ ꢁH type hydrogen bonding in the molecule. The conjugation
and influence of intermolecular hydrogen bonding (C@Oꢁ ꢁ ꢁH type)
network in the crystal results in lowered C@O stretching wave-
number. Hydrogen bonding affects carbonyl wavenumbers, but
the effects are more pronounced when hydrogen banding is com-
bined with mesomeric effects. When a carbonyl group is partici-
pating in hydrogen bond and resonance [54–57] can occur, which
puts a partial negative charge on the oxygen atom accepting the
hydrogen bond and a positive charge on the atom donating the
hydrogen, the partial ‘‘transfer of allegiance’’ of the proton en-
hances resonance [C@Oꢁ ꢁ ꢁHAXꢂ M CAOꢂꢁ ꢁ ꢁHAX+@] and lowers
the C@O stretching wavenumbers [54–57]. The bands calculated
at 1079 cmꢂ1 and 749 cmꢂ1 are identified as C@O in plane bending
and out-of-plane bending modes while the normal modes ob-
served at 1086 cmꢂ1 and 752 cmꢂ1 are identified as in plane C@O
bending and out-of-plane bending vibrations.
Fig. 2. HOMO LUMO plot of 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one by
B3LYP/6-311++G (d,p) level of theory.
Benzimidazole ring vibrations
The CAH ring stretching vibrations of heterocyclic compounds
are normally found between 3100 and 3000 cmꢂ1 [54–57]. For
BHMB, the very weak absorption bands at 3074 and 3032 cmꢂ1
in FT-IR and the bands at 3070 cmꢂ1 in FT-Raman are assigned to
CAH stretching modes of the ring system. The scaled theoretical
values at B3LYP/6-311++G (d,p) of ring CAH stretching modes
are 3059 cmꢂ1 and 3037 cmꢂ1 with a PED of 99%. The (C@C) vibra-
tions are more interesting if the double bonds are in conjugation
with the ring. The actual positions are determined not so much
by the nature of the substituent but by the form of substitution
around the ring [54–57]. For benzimidazole ring IR bands at
1620, 1610, 1410 cmꢂ1 and 1305 cmꢂ1 are assigned to C@C
stretching and the counterpart in Raman are 1620, 1412 and
1385 1278 cmꢂ1 in which the mode corresponding to 1610 cmꢂ1
have a high PED of 61%. The weak band at 1152 and 977 cmꢂ1 in
Raman for CAC stretching corresponds to the benzimidazole. Most
of the C@C stretching modes in this region are coupled with CAH
in plane bending mode. The identification of CAN vibrations is a
Fig. 3. Molecular electrostatic potential mapped on the q(r) = 0.0004 a.u. isodensity
surface for 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one in the range from
ꢂ6.094Eꢂ2 (red) to +6.094Eꢂ2 (blue). (For interpretation of the references to colour
in this figure legend, the reader is referred to the web version of this article.)

438
L. Joseph et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440

L. Joseph et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440
439
Fig. 4. (a) Simulated IR spectra of 1, 3-Bis (hydroxymethyl) benzimidazolin-2-one
by B3LYP/6-311++G (d,p) level of theory and (b) Experimental FT-IR spectra in the
range 4000–400 cmꢂ1
.
Fig. 5. (a) Simulated Raman spectra 1, 3-Bis (hydroxymethyl) benzimidazolin-2-
one by B3LYP/6-311++G(d,p) level of theory and (b) experimental FT-Raman spectra
in the range 3600–50 cmꢂ1
.
difficult task, since the mixing of vibrations is possible in this re-
gion. However, with the help of the force field calculations, the
CAN vibrations are identified and assigned in this study. James
et al. [61] assigned 1370 cmꢂ1 for 1-benzyl-1-H-imidazole for
CAN vibration. Pinchas et al. [62] assigned the CAN stretching
at 1368 cmꢂ1 in benzamide. For BHMB molecule the observed
band at 1371 cmꢂ1 in IR are assigned to CAN stretching, in which
1363 cmꢂ1 have PED of 24%. The corresponding Raman active
band is observed at 1365 cmꢂ1. The CAN stretching is assigned
to the wavenumber 977 cmꢂ1 with 34% PED. The in-plane and
out-of-plane bending vibrations assigned in this study are also
supported by the literature [16–20]. The CAH in plane bending
vibrations of benzimidazole is coupled with ring CAC and CAN
stretching modes (Table 4). IR active CAH in plane bending of
benzimidazole appears at 1165 cmꢂ1 and 1015 cmꢂ1 with signif-
icant PED (>60%). The Raman active bands at 1168 cmꢂ1 and
1016 cmꢂ1 are corresponding to CAH in plane bending mode of
benzimidazole. CAH out of plane bending of benzimidazole ring
is active in IR at 862 and 829 cmꢂ1 with a PED more than 70%.
The Raman counterpart occurs as a weak band at 832 cmꢂ1
.
The ring puckering modes usually appears in IR and is absent
or appears as a weak band in Raman. In IR spectra the ring
puckering modes occur at 728 cmꢂ1 for benzimidazole. The

440
L. Joseph et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 432–440
[18] T.S. Xavier, Naghmana Rashid, I. Hubert Joe, Spectrochim. Acta Part A Mol.
Biomol. Spectrosc. 78 (2011) 319–326.
asymmetric CAC deformation for benzimidazole is active for the
band at 577 cmꢂ1 in Raman and the corresponding mode in IR is
at 574 cmꢂ1 with a PED of 44%. Asymmetric torsion for benzimid-
azole ring is Raman active at 424, 170 and 137 cmꢂ1. The butterfly
mode is Raman active at 225 cmꢂ1 with a PED 29%.
[19] V. Krishnakumar, R. Ramasamy, Spectrochim. Acta Part
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Molecular structure and vibrational wavenumbers of BHMB is
studied using vibrational spectra and density functional method.
The DFT based calculations for BHMB reproduced its experimental
geometry and vibrational wavenumbers excellently. The NBO anal-
ysis reveals the reasons for hyperconjugative interaction, ICT and
stabilization of the molecule. A complete vibrational analysis of
BHMB was performed on the basis of the SQM force field obtained
by DFT calculation. The wavenumbers proposed by PED calcula-
tions are in fair agreement with the observed wavenumbers. The
red shifting of OAH stretching wavenumber is due to intermolec-
ular hydrogen bonding. The lowering and splitting of the carbonyl
stretching vibrational modes is assigned to the intermolecular
association based on C@Oꢁ ꢁ ꢁH type hydrogen bonding in the mol-
ecule. Lower value of the HOMO and LUMO energy gap reveals the
significant degree of charge transfer interactions taking place with-
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One of the authors Lynnette Joseph thanks the University
Grants Commission (UGC), New Delhi, India, for the financial sup-
port MRP(S)-899/10-11/KLKE002/UGC-SWRO.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.05.003.
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