Vibrational spectroscopy investigation and density functional theory calculations on (E)-N′-(4-methoxybenzylidene) benzohydrazide

Article abstract of DOI:10.1016/j.saa.2015.02.016

The FT-IR, FT-Raman and UV-Vis spectra of the Schiff base compound (E)-N′-(4-methoxybenzylidene) benzohydrazide (MBBH) have been recorded and analyzed. The optimized geometrical parameters were calculated. The complete vibrational assignments were perform

Full text of DOI:10.1016/j.saa.2015.02.016

Accepted Manuscript
Vibrational Spectroscopy investigation and density functional theory calcula-
tions on (E)-N’-(4-methoxybenzylidene) benzohydrazide
H. Saleem, S. Subashchandrabose, N. Ramesh Babu, M. Syed Ali Padusha
PII:
S1386-1425(15)00168-7
http://dx.doi.org/10.1016/j.saa.2015.02.016
SAA 13306
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
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Revised Date:
Accepted Date:
15 October 2014
9 December 2014
4 February 2015
Please cite this article as: H. Saleem, S. Subashchandrabose, N. Ramesh Babu, M. Syed Ali Padusha, Vibrational
Spectroscopy investigation and density functional theory calculations on (E)-N’-(4-methoxybenzylidene)
benzohydrazide, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://
dx.doi.org/10.1016/j.saa.2015.02.016
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Vibrational Spectroscopy investigation and density functional theory
calculations on (E)-N'-(4-methoxybenzylidene) benzohydrazide
H. Saleema, S. Subashchandraboseb*, N. Ramesh Babuc, M. Syed Ali Padushad,
aDept. of Physics, Annamalai University, Annamalainagar -608002, Tamil Nadu, India.
bCentre for research and development, PRIST University, Thanjavur-613403
cDept. of Physics, M.I.E.T. Engineering College, Trichy-620007, Tamil Nadu, India.
dPG and Research Dept. of Chemistry, Jamal Mohamad College (Autonomous), Tirchy -620020, Tamil Nadu, India.
ABSTRACT
The FT-IR, FT-Raman and UV-Vis spectra of the Schiff base compound (E)-N’-(4-
methoxybenzylidene) benzohydrazide (MBBH) have been recorded and analyzed. The optimized
geometrical parameters were calculated. The complete vibrational assignments were performed
on the basis of TED of the vibrational modes, calculated with the help of SQM method. NBO
analysis has been carried out to explore the hyperconjugative interactions and their second order
stabilization energy within the molecule. The Molecular orbitals (MO’s) and its energy gap were
studied. The first order hyperpolarizability (β0) and related properties (β, α0, Δα) of MBBH are
also calculated. All theoretical calculations were performed on the basis of B3LYP/6-
311++G(d,p) level of theory.
Keywords: FT-IR; FT-Raman; TED; NBO; MBBH;
*Corresponding author
E-mail: sscbphysics@gmail.com,
Mobile: +91 9976853476.

1 Introduction
Hydrazides, the acylated derivatives [1] of hydrazine are being useful for number of
biological properties. Hydrazides are important starting materials for a wide range of derivatives
utilizable in pharmaceutical products and as surfactants. Hydrazides have been known to be
associated with antibacterial [2], antifungal [3], anthelmintic [4] and anticonvulsant [5] activities.
Biological assessment of fatty hydrazide and their derivatives have been the focus of earlier
investigative studies [6, 7]. The fatty hydrazides are further derivatised to obtain new
antibacterial and antifungal agents. Acyl hydrazones, 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 [8-11].
P-Hydroxybenzohydrazide moiety and its analogs seemed to be suitable parent
compounds upon which variety of biological activities were reported such as antitumor [12],
antianginal [13], antitubercular [14], antihypertensive [15] and antibacterial [16]. Hydrazides
have recently become attractive to theoreticians as well as experimentalists due to the biological
significance particularly in medicinal and enzyme chemistry. Harmonic force fields of
polyatomic molecules play a vital role in the interpretation of vibrational spectra and in the
prediction of other vibrational properties. IR spectra of N-benzoylhydrazine (BHZ)
phCONHNH2 and its uranyl complex have been [17] studied in the 4000–50 cm−1 frequency
range. Complete equilibrium geometry of the ligand molecule has been determined by DFT and
BLYP/6-31G force field calculations. A complete vibrational assignment of the solid state IR
and Raman spectra of BHZ was performed on the basis of NCA of a single molecule. In this
present study, MBBH molecule was synthesized and the spectral characterizations were made by
2

FT-IR, FT-Raman and UV-Visible spectra and the corresponding theoretical predictions were
carried out by using B3LYP/6-311++G(d,p) level of calculation.
2 Experimental details
2.1 Synthesis
The 3.0 ml (0.025 mol) ethanolic solution of anisaldehyde was added to (0.025 mol) 3.4 g
of benzohydrazide. The reaction mixture was taken in a round bottom flask and kept over a
magnetic stirrer and stirred well in ice cold condition for two hours. The white precipitate
obtained was filtered and dried over vacuum.
2.2 FT-IR, FT-Raman and UV-Visible details
The FT-IR spectrum of MBBH was recorded in the region of 400-4000 cm-1 on an IFS
66V spectrophotometer using the KBr pellet technique. The spectrum was recorded in room
temperature with a scanning speed of 10 cm-1 per minute at the spectral resolution of 2.0 cm-1 in
the SAIF Laboratory, IIT(M), Tamilnadu, India. The FT-Raman spectrum of the title compound
was recorded by using the 1064 nm line of a Nd: YAG laser as an excitation wavelength in the
region of 50-3500 cm-1 on Bruker model IFS 66V spectrophotometer equipped with an FRA 106
FT-Raman module accessory at the spectral resolution of 4 cm-1. The FT-Raman spectrum was
recorded from the SAIF Laboratory, IIT(M), Tamilnadu, India. The ultraviolet absorption
spectrum of MBBH was recorded in the range of 200-500 nm by using a Perkin Elmer Lambda-
35 spectrometer and UV pattern was taken from a 10-5 molar solution of MBBH dissolved in
methanol.
3 Computational details
In order to establish the stable possible conformers, the conformational space of MBBH
compound was scanned with molecular mechanic simulations. For meeting the requirements of
3

accuracy and computing economy, theoretical methods and basis sets were considered. The
Density Functional Theory (DFT) has been proved to be extremely useful in treating electronic
structure of molecules. The entire calculations were performed at B3LYP/6-311++G (d, p) level
of basis set using Gaussian 03W [18] program package, invoking gradient geometry optimization
[18, 19]. The optimized structural parameters were used in the vibrational frequency calculations
at the DFT level to characterize all the stationary points as minima. The vibrationaly averaged
nuclear positions of MBBH were used for harmonic vibrational frequency calculations resulting
in IR and Raman frequencies together with intensities and Raman depolarization ratios. The
vibrational modes were assigned on the basis of TED analysis using the Scaled quantum
mechanical program [20].
The Raman activity was calculated by using Gaussian 03W package and the activity was
transformed into Raman intensity using Raint program [21] by the expression:
1
i
Ii 1012 (0 i )4   RA
(1)
i
Where Ii is the Raman intensity, RAi is the Raman scattering activity, νi is the
wavenumber of the normal modes and ν0 denotes the wavenumber of the excitation laser [22].
4 Results and Discussion
4.1 Molecular Geometry
The optimized geometrical parameters namely bond lengths, bond angles and dihedral
angles calculated by B3LYP/6-311++G(d,p) level are listed in Table 1. The optimized molecular
structure of MBBH and the atom numbering scheme is shown in Figure 1. The optimized
structural parameters are compared with the experimental X-ray data for MBBH [23]. In the ring
part (both ring 1, 2), the optimized geometries of the molecule show good agreement with X-ray
4

data. The bond lengths (ring 1) of C1-C2, C2-C3, C3-C4, C4-C5, C5-C6 and C1-C6 are calculated as
1.407, 1.387, 1.403, 1.404, 1.391 and 1.404 Å and their corresponding recorded values (XRD)
are 1.389, 1.387, 1.383, 1.383, 1.373 and 1.384 Å [23], respectively. Similarly for ring 2, the
bond lengths of C23-C24, C24-C25, C25-C26, C26-C27, C27-C28 and C23-C28 are calculated as 1.403,
1.395, 1.395, 1.397, 1.392 and 1.401 and their corresponding recorded values are as 1.382,
1.393, 1.363, 1.370, 1.376 and 1.383 Å. The CH bond lengths of ring 1 and ring 2 are almost
equal. In this study, the most significant difference was seen in bond lengths of C1-C7 (1.460 Å)
and C21-C23 (1.503 Å). In MBBH, the hydrazone linkage plays an important role. For the
carbonyl (C21=O22) group bond length in hydrazone link was observed at 1.224Å which is
exactly matches with the literature [24], whereas the calculated bondlength was about 1.219Å.
The bondlength of >N19–C21< group was observed at 1.350Å whereas the computed value is
1.388Å. The bond N18-N19 behaves as a bridge between the two rings and its observed value is
about 1.388Å, whereas the calculated value is about 1.356Å, it found support from the literature
[24]. Similarly the bondlength of C17=N18 is about 1.269 and 1.284Å as observed and calculated
values respectively and which are coincided well with the literature [25].
The bond angle of N18-N19-C21 was calculated about 120.8° whereas the observed value is
121.29°. The N19-C21=O22 (123.2°) bond angle is (3°) positively deviated from [25] (N19-
C21=O22). This may be due to the attachment of ring 2 with C21 atom. Similarly the dihedral
angle H20-N19-C21-O22:167.8° is positively (167.3°) deviated from our earlier study [25] (H20-
N19-C21-O22: -0.5°) which shows that the hydrazone linkage is in chair form rather than boat
form. The asymmetries of the benzene rings are also evident from the positive and negative
deviation from the normal value of 120°. The bond angles C6-C1-C7: 122.0° (ring 1), C21-C23-
C24: 123.8° (ring 2) are greater than C2-C1-C7: 119.7° (ring 1), C21-C23-C28: 117.0° (ring 2)
5

because of interaction between hydrazone group and hydrogen atom (ring 1)/oxygen atom (ring
2). The C4-O10-C11 bond angle is 118.4°, which is in excellent agreement with X-ray value
(118.0°).
4.2 Vibrational assignments
The molecule under study possesses C1 point group symmetry. The title compound
MBBH consists of 33 atoms, which makes 93 normal modes of fundamental vibrations, which
span the irreducible representations: 63A’+30A". All the 93 fundamental vibrations of the
molecular are both IR and Raman active. Because of the anharmonicity of the incomplete
treatment of electron correlation and the use of finite one-particle basis set, the calculated
harmonic vibrational wavenumbers are usually higher than the experimental vibrational
wavenumbers [26]. The harmonic frequencies were calculated by B3LYP method using 6-
311++G(d,p) basis set. The experimental and theoretical frequencies and their assignments are
presented in Table 2. The combined experimental and theoretical spectra (IR and Raman) of
MBBH are shown in Figure 2 and Figure 3, respectively. The vibrational band assignments were
made by using the TED analysis.
4.2.1 C-H Vibrations
The C-H stretching vibrations of aromatic molecule are expected to appear in the
frequency range of 3000-3100 cm-1[27,28]. In this study, the FT-IR bands identified at 3063,
3025 cm-1 and the Raman counterpart at 3066 cm-1 are attributed to C-H stretching mode. For the
same mode the scaled wavenumbers are in the range 3036-3082 cm-1 (mode nos: 2-10). These
assignments are in line with the literature [27, 28] and also find support from TED values
(~91%). The C-H in-plane bending vibrations appear by sharp but weak to medium intensity
6

bands in the frequency region 1100-1500 cm-1. These bands are not sensitive to the nature of
substituents [29]. The C-H in-plane bending vibrations observed at 1457, 1305, 1286 cm-1 in FT-
IR and 1288, 1227 and 1140 cm-1 in FT-Raman spectrum. And their corresponding calculated
values are 1477, 1460, 1418, 1299, 1287, 1232, 1207, 1144 and 1117 cm-1 (mode nos: 22, 23, 27,
30, 31, 34, 35, 39 and 42).
The C-H out-of-plane bending vibrations usually occur in the wavenumber range 750-
1000 cm-1 [27,28]. The C-H out-of-plane bending vibrations for the title compound identified at
968, 913 and 831 cm-1 in FT-IR and 1001 and 915 cm-1 in FT-Raman spectra. For the same mode
the predicted values are 1006, 977, 970, 941, 906, 828, 826 and 810 cm-1 (47, 49, 50, 52, 55, 57,
58, 59). These results are found to be good agreement with literature [30]. The stretching, in-
plane and out-of-plane vibrations of C7-H17 assigned to mode nos: 13, 29 and 52 which are in
agreement with literature [31].
4.2.2 Phenyl ring vibrations
The ring carbon-carbon stretching vibration occurs in the region 1430-1625 cm-1.
Varsanyi [32] have assigned the ѵC-C vibrations in the regions of 1590-1625, 1575-1590, 1470-
1540, 1430-1460 and 1280-1380 cm-1 with variable intensity of bands. For the title compound
(MBBH), the FT-IR bands observed at 1572, 1550, 1058 cm-1 and the FT-Raman bands recorded
at 1569, 1056 cm-1 are belongs to ѵC-C mode. The wavenumbers predicted by B3LYP/6-
311++G(d,p) method in the range of 983-1580 cm-1 mode nos: 17-20, 28, 35, 36, 42-44 and 48
are in line with Varsanyi [32].
The C-C in-plane bending vibrations observed at higher frequencies than the C-C out-of-
plane bending vibrations. The C-C-C in-plane-bending vibrations are assigned to 953, 930, 791,
7

667, 623, 608 and 583 cm-1 (mode nos: 51, 53, 60, 66-69); and the C-C-C out-of-plane bending
vibrations are calculated at 517, 495, 414, 401, 383, 279 and 185 (mode nos: 70, 72, 74, 76, 78,
80, 85) by B3LYP method, in which the mode nos: 70, 85 are in agreement with observed values
534 cm-1 (FT-IR) and 182 cm-1 (FT-Raman). The calculated bands 1280 and 1232 cm-1 (mode
nos: 33, 34) are due to contributions of C21-C23 and C1-C7, respectively. The ѵC1-C7 mode is
observed as medium band at 1227 cm-1 in the FT-Raman spectrum.
4.2.3 C-N and C=N Vibrations
The identification of C=N, C-N vibrations are very difficult task [33], since the mixing of
several bands are possible in the region. Generally the ѵC=N vibration observed in the region of
1600-1670 cm-1 [34]. For the title compound MBBH, the C=N stretching vibration observed as
very strong bands at 1604 cm-1 in FT-IR and 1598 cm-1 FT-Raman spectra. The C7=N18
stretching frequency is in agreement with theoretical value (1609 cm-1: mode no: 16) and is
further supported by TED value (78%). Silverstein et al. [28] assigned C-N stretching absorption
in the region 1266-1382 cm-1 for aromatic amines. The C-N stretching vibration was assigned at
1360 cm-1 in the case of benzaldehyde phenylhydrazone [35]. In this study, the C21-N19
stretching vibration assigned to mode no. 33 (1280 cm-1). The βC1-C7=N18, βC23-C21-N19 and ГC1-
C7=N18, ГC23-C21-N19 are calculated at 1117, 583 cm-1 (mode nos: 42, 69) and at 185, 110 cm-1
(mode nos: 85, 87), respectively, in which mode no: 85 is in line with observed Raman value
(182 cm-1).
4.2.4 C-O and C=O Vibrations
In carbonyl group, the absorption is sensitive for both the carbon and oxygen atoms.
Normally the C-O stretching vibration occurs in the region 1000-1260 cm-1 [36]. The ѵC4-O10
mode has been assigned at 1249 (FTIR)/1248 cm-1 (Raman) for 4-methoxy-2-methyl benzoic
8

acid by Meganathan et al. [37]. Based on the above conclusion the band observed at 1258 cm-1 is
assigned to ѵC-O mode, which is supported by harmonic frequency value 1280 cm-1 (mode no:
32). In general, the IR absorption in the range 1650-1750 cm-1 is for ketones, aldehydes and
amides [28] Conjugation, ring size, hydrogen bonding, steric and electronic effects often result in
significant shift in C=O absorption frequencies [38]. Arjunan et al. [31], assigned stretching
vibration for benzohydrazide at 1661 cm-1 in the IR spectrum. According to the literature, the
C21=O22 stretching vibration is assigned at 1641 cm-1 in the IR spectrum and its corresponding
harmonic value is 1685 cm-1 (mode no. 15). This assignment is further supported by TED value
(84%).
In this study, the reported value of 1641 cm-1 for ѵC=O vibration is below the expected
range. It may be due to the conjugation of the C=O bond with aromatic ring may increase its
single bond character, result in lowered values of C=O stretching wavenumbers. The same trend
was also observed in P-hydroxyacetophenone [39] and 3-aminoacetophenone [40]. The intensity
of the carbonyl group can increase because of conjugation (or) formation of hydrogen bonds.
The increase in conjugation, therefore leads to the intensification of Raman lines as well as the
increased IR band intensities [41]. Arjunan et al.,[31] assigned the C=O in-plane bending mode
for benzohydrazide to the wavenumber at 685 cm-1 (FT-IR) and at 681 cm-1 (FT-Raman).
Similarly, the C=O out-of-plane mode for the same is assigned to the wave number at 415 cm-1
(FT-Raman). In this study, the bands calculated at 896, 509, 263 cm-1 (mode nos: 56, 71, 81) and
773, 229, 690 cm-1 (mode nos: 61, 82, 64) are assigned as the deformation bands (in-plane and
out-of-plane) of βNC=O, βCOC,
β
and ГNC=O, Г COC, ГCCO, respectively. Mode no: 71 is in
CCO
agreement with literature[42] in the case of 6-methoxy purine (517 cm-1: FT-IR).
9

4.2.5 Methyl group vibrations
The title molecule possesses one CH3 group in the para-position of the ring along with
O10 atom. Methyl groups are generally referred to as electron-donating substituents in the
aromatic ring system. For the assignment of CH3 group frequencies, nine fundamentals can be
associated with each CH3 group, namely the symmetrical stretching in CH3 (CH3 symmetric
stretch) and asymmetrical stretching (CH3 asymmetric stretch), in-plane stretching modes (in-
plane hydrogen stretching mode), the symmetrical (CH3 symmetric deform) and asymmetrical
(CH3 asymmetric deform) deformation modes, the in-plane rocking (CH3 in-plane rocking), the
out-of-plane rocking (CH3 out-of-plane rocking) and twisting (twisting CH3) bending modes.
The methyl hydrogen atoms in MBBH are simultaneously subjected to hyperconjugation and
back donation, which causes the decrease in stretching wave numbers and IR intensities [43].
The C-H symmetric stretching mode of CH3 group appears in the region 2825-2870 cm-1
for O-CH3 group substituted compounds [44], which is lower in magnitude compared with the
value of CH3 substitutes compounds lies in the region 2860-2935 cm-1. The asymmetric
stretching mode for the above two types (i.e. O-CH3 and CH3), lies in the same region 2924-2985
cm-1. For the title compound MBBH, the asymmetric and symmetric stretching vibration of CH3
have been identified at 3014, 2949 and 2883 cm-1 (mode nos: 11, 12 and 14), respectively by
B3LYP/6-311++G(d,p) method. The observed FT-IR band at 2927 cm-1 is assigned to C-H
asymmetric vibrations. This assignment is in good agreement with literature [25] (2929 cm-1: FT-
IR). These assignments are also find support from TED values 100%.
Unlike the C-CH3 group, the stretching bands of O-CH3 are expected in a wider range
due to their difference in orientation with the major lobe of oxygen lone pairs [45]. The
asymmetric and symmetric bending vibrations of methyl group usually appear in the regions of
10

1440-1465 cm-1 and 1370-1390 cm-1, respectively [34]. The βHCH (asymmetric) mode has been
identified with the frequencies at 1445cm-1 (mode no: 24). The intense bands around 1420/1420
cm-1 in the FT-IR/FT-Raman spectra corresponds to the symmetric bending mode (βHCH) and this
is in excellent agreement with harmonic value 1419 cm-1 (mode no: 26).
4.2.6 O-CH3 vibrations
The O-CH3 vibration mode is assigned at ~1040 cm-1 for anisole [46] and in the region of
1000-1100 cm-1 for anisole and its derivatives [47-50]. This mode is assigned at 1026, 909 and
995 cm-1 for o-, m- and p-methoxybenzaldehydes, respectively. The intense FT-IR band at 1025
cm-1 represent the O-CH3 stretching vibration of MBBH, while the corresponding harmonic
wave no is 1035 cm-1 (mode no: 45). This mode is further justified with the help of Gauss View
visualization program. This assignment is also supported by the above literature in addition to
TED: 71% output.
Venkataram reddy and Ramana Rao [50] have proposed an assignment for δC-O-CH3 mode
in the region of 300-670 cm-1 for anisole and its derivatives. As this mode lies in the region of
the ring planar C-C-C angle bending modes, a strong mixing amongst these two modes and other
planar modes is expected [36]. In accordance with above conclusions, the harmonic wavenumber
263 cm-1 (mode no: 81) attributed to βC4O10C11 mode. It should be emphasized that the
wavenumber calculated at 263 cm-1 for βC4O10C11 is missing in both FT-IR and FT-Raman
spectra. Our calculated frequency 76 cm-1 (mode no: 89) agrees well with the band at 74 cm-1
observed in the FT-Raman spectrum assigned to ГC3C4O10C11 mode. These assignments are in
agreement with literature [25] and also find support from TED output: 60%. The torsion mode of
the O-CH3 group was observed for anisole at 100 cm-1 by Anto et al. [51]. The assignments of
11

the wavenumbers calculated at 1201, 1137 and 229 cm-1 (mode nos: 36, 40 and 82) are attributed
to βH13H12C11O10 and ηH12C11O10C4 modes, respectively.
4.2.7 N-N and N-H vibrations
Ravikumar et al. [35] assigned the ѵN-N and δCNN modes at 1128 cm-1 (IR)/1137 cm-1
(Raman) and at 912 cm-1 (Raman), respectively. A moderate coincidence of theoretical value
1155 cm-1 /mode no. 37 with that of experimental values (1168: FT-IR/1169 cm-1: FT-Raman) is
found in the ѵN18-N19 vibration of MBBH. The CNN scissoring vibration is assigned to mode no:
75/411 cm-1. In general, the N-N stretching frequencies occur in the region 3000-3500 cm-1 [52]
with reference to this, the vibrational frequency observed at 3422 cm-1 in the FT-IR spectrum and
the corresponding harmonic frequency 3367 cm-1 /mode no: 1 is assigned to ѵN-H mode. This
mode is well agreed with TED (100%) result. The N-H in-plane bending mode was observed at
very strong band in Raman at 1569 cm-1 [35]. The frequency of the βN18N19H20 vibration is
calculated to be 1497 cm-1 (mode no: 21) for MBBH. This mode is observed in the FT-IR
spectrum (1511 cm-1) with strong intensity. The observed/calculated (460: FT-IR/ 482: mode no:
73) frequency assigned to ηH20N19N18C7 mode.
4.3 Non-Linear Optical properties
The first order hyperpolarizabilities of MBBH was calculated using B3LYP/6-
311++G(d,p) level of basis set, based on the finite-field approach. In the presence of an applied
electric field, the energy of a system is a function of the electric field. The first order
hyperpolarizability is a third rank tensor that can be described by a 3x3x3 matrix. The 27
components of the 3D matrix can be reduced to 10 components due to Kleinman symmetry [53].
It can be given in the lower tetrahedral format. It is obvious that the lower part of the 3x3x3
matrices is a tetrahedral. The components of β are defined as the coefficients in the Taylor series
12

expansion of the energy in the external electric field. When the external electric field is weak and
homogeneous, this expansion becomes:
E  E0   F 1/ 2 F F 1/6 F F F
(2)




Where E0 is the energy of the unperturbed molecules, Fα is the field at the origin, and
 , ,
 is the components of the dipole moment, polarizability and the first order
hyperpolarizabilities respectively. The total static dipole moment μ, the mean polarizability α0,
the anisotropy of polarizability Δα and the mean first order hyperpolarizability β0, using the x, y,
z components are defined as
  (x2  y2  z2 )1/2
(3)
xx yy zz
0 
(4)
3

1/2
  21/2   2    2    2  6 2 2 2
(5)
(6)

xx 

yy 

zz 

xz 

xx
yy
zz
xy
yz



1/ 2
0 

x2  y2  z2

Many organic molecules, containing conjugated π electrons were characterized by large values
of molecular first order hyper polarizabilities and analyzed by means of vibrational spectroscopy
[54-57]. The intra-molecular charge transfer from the donor to acceptor group through a
single-double bond conjugated path can induce large variations on both the molecular
dipole moment and the molecular polarizability [58].
The conjugated π electron-containing organic molecules which characterized by large
values of molecular first hyperpolarizabilities have been investigated by means of vibrational
13

spectroscopy [59]. The significance of the polarizability and the first hyperpolarizability of
molecular systems depend on the efficiency of electronic communication between acceptor and
the donor groups, since it is the basis to intra-molecular charge transfer [60]. The intra-molecular
charge transfer from the donor to the acceptor group through single-double bond conjugated path
can induce large variations of both the molecular dipole moment as well as molecular
polarizability, making IR and Raman activity strong at the same time [61]. It is well known that
the movement of p electron from donor to acceptor group makes the molecule highly polarizable.
As a consequence, the intra-molecular charge transfer interaction may be responsible for the
NLO properties of MBBH. The molecular hyperpolarizability get enhanced in organic molecules
containing O−H, N−H and C=O groups, which are involved in hydrogen bond interactions [62].
It is believed that this type of hydrogen bonding is the main source of non-linear crystal like
urea.
The molecular electronic dipole moment, molecular polarizability and molecular first
hyperpolarizabiliy of MBBH were calculated using B3LYP/6-311++G(d,p) level and results are
given in Table 3. The Dipole moment was calculated as 0.2143, 1.2592 and -0.1713 Debye and
the maximum contribution is in the y-direction. Whereas, the dipole moment is about 1.2887
Debye, the first hyperpolarizability (β0) of MBBH is calculated as 26.03x10-30 esu, which is sixty
nine times greater than that of urea (0.3728x10-30 esu). Hence this molecule has considerable
NLO activity.
4.4 NBO analysis
14

The hyperconjugation gives as stabilizing effect that arises from an overlap between an
occupied orbital with another neighboring electron deficient orbital, when these orbitals are
properly oriented. This non-covalent bonding (antibonding) interaction can be quantitatively
described in terms of the NBO analysis, which is expressed by means of the second-order
perturbation interaction energy (E(2)) [63-66]. This energy represents the estimate of the off-
diagonal NBO Fock matrix elements. It can be deduced from the second-order perturbation
approach [67]
F(i, j)2
 j i
E(2)  Eij  qi
(7)
Where qi is the donor orbital occupancy, εi and εj are diagonal elements (orbital energies) and
F(i,j) is the off diagonal NBO Fock matrix elements.
The importance of the NBO method is originated from it gives information about the
intra and inter-molecular bonding and interactions among bonds. Furthermore, it provides a
convenient basis for investigating the interactions in both filled and virtual orbital spaces along
with charge transfer and conjugative interactions in molecular system [68]. NBO analysis was
performed for MBBH by using B3LYP level with the 6-311++G(d,p) basis set in order to
elucidate the intra-molecular, hybridization and delocalization of ED within MBBH. The strong
intra-molecular hyperconjugative interaction of the ζ and π electrons of C−C to the anti C−C
bond of the benzene ring leads to stabilization of some part of the benzene ring [67].
Natural (localized) orbital used in computational chemistry to calculate the distribution of
ED in atoms and in bonds between atoms. They have the “maximum occupancy character” in
localized 1-center and 2-center regions of the molecule [69]. The second order perturbation
analysis of Fock matrix, Lewis and Non-Lewis NBO analysis of MBBH calculated by B3LYP
15

method with 6-311++G(d,p) basis set are listed in Table 4(a) and Table 4(b). Table 4(a) lists the
calculated second order interaction energies E(2) between the donor and acceptor orbitals in
MBBH. In this study, the ζ bonds have higher ED than the π bonds. Due to this reason, the ζ–ζ*
transitions have minimum delocalization energy than the π–π* transitions. In accordance with
this, the title molecule shows maximum stabilization energy of 420.87 kJ/mol of energy during
the interaction between π C23-C24 and π*C21-O22 respectively. It could be observed that the
bonding C23-C24 electron has 49.13% of C24 character in sp1.81 hybrid and 50.87% of C23
character in sp1.81 hybrid. The sp1.81 hybrid on C24 has 64.42 p-characters and sp1.81 hybrid on
C23 has 64.39 p-character. The coefficients 0.7132 and 0.7010 obtained are called polarization
coefficients of C23 and C24. Whereas it anti-bonding C23-C24 electron has 48.88% of C24 character
in sp99.99 hybrid and on C23 has 51.12% of C23 character in sp99.99 hybrid. The sp99.99 of C24
has 99.98 p-character and sp99.99 hybrid on C23 has 99.99 p-character. The sizes of these
coefficients show the importance of the two hybrids in the formation of the bond.
The larger the E(2) value shows the intensive interaction between electron donors and
electron acceptors. In our title molecule MBBH, π(C23-C24)→π*(C21-O22) interaction has 420.87
kJ/mol, π(C7-N18)→π*(C1-C2) interaction has 386.14 kJ/mol and ζ(N19)→ζ*(C21-O22)
interaction has 185.35 kJ/mol and hence they give stronger stabilization to the structure. The
maximum hyperconjugative E(2) energy of heteroatoms during the intra-molecular interaction
leads the molecule towards medicinal and biological applications. The lone pair of oxygen and
nitrogen atom plays great role in the molecule. The O22 atom transfers 117.95 kJ/mol and 79.08
kJ/mol to π*N19-C21 and π*C21-C23 bonds, respectively. In the same way the N19 transfers
122.21 kJ/molto ζ*C7-N18 and 185.35 kJ/mol to ζ*C21-O22, respectively. The variation in
energies has been observed in NBO are due to inter and intra-molecular interactions of the
16

molecules [70]. The conjugation oxygen lone pair orbital with π orbital of phenyl will be strong
when both orbitals lie in a same plane and will be weak when they are in perpendicular planes
[71]. In this work, O10 atom transfer 116.27 kJ/mol and 22.97 kJ/mol to C3-C4 and C11-H13
bonds, respectively.
4.5 HOMO-LUMO analysis
HOMO and LUMO are the very important parameters for quantum chemistry. The energy values
of HOMO (π-donor) and LUMO (π-acceptor) and their energy gap reflects the chemical activity
of the molecule. The energy gap between HOMO and LUMO has been used to prove the Bio-
activity from ICT [72]. The HOMO and LUMO energy calculated by B3LYP/6-311++G(d,p)
method. The frontier molecular orbitals of MBBH are listed in Table S1 (Supporting
information). The atomic compositions of frontier molecular orbitals are shown in Figure 4. The
HOMO is located over the oxygen atoms, hydrazine linkage and ring1, the HOMO→LUMO
transition implies an ED transfer to ring 2 and methyl group. The HOMO and LUMO energies
are predicted as 5.919 eV and 1.786 eV, respectively. The HOMO and LUMO energy gap is
4.132 eV, which explains the eventual charge transfer interactions taking place within the
molecule.
4.6 Molecular electrostatic potential
The MEP is widely used as a reactivity map displaying most probable regions for the
electrophilic attack of charged point-like reagents on organic molecules. MEP plot provides a
simple way in predicting the interaction of different geometries. In order to predict the reactive
sites for electrophilic and nucleophilic attacks of the title molecule, MEP was calculated with
B3LYP/6-311++G(d,p) basis set. The negative (red color) and positive (blue color) regions of
17

MEP are related to electrophilic and nucleophilic reactivity, respectively shown in Figure 5. The
negative region is located over the O22 atom and the positive region is located over H20 atom in
the hydrazone linkage.
4.7 UV analysis
The UV absorption spectrum of MBBH recorded in the range 250-450 nm. All the
structures allow strong π-π* (or) ζ-ζ* transition in the UV-Vis region with high extinction
coefficients. On the basis of fully optimized ground state structure, TD-DFT/B3LYP/6-
311++G(d,p) calculations has been used to determine the low-lying excited states of MBBH. The
calculated results involving the vertical excitation energies, oscillator strength (f) and wavelength
are carried out and compared with measured experimental wavelength. Typically, according to
Franck-Condon principle, the maximum absorption peaks (λmax) in a UV-Vis spectrum
corresponds to vertical excitation. It is evident from the Table 5, that the calculated absorption
maxima values have been found to be 327, 288 and 282 nm which correlates well with the
experimental values 349 and 299 nm. The combined experimental and theoretical UV-Vis
absorption spectra are shown in Figure 6.
4.8 Mulliken charges
Mulliken atomic charge calculation has an important role in the application of quantum
chemical calculation to molecular system. Because the atomic charges affect dipole moment,
polarizability, electronic structure and more a lot of properties of molecular systems. The total
atomic charges of MBBH are calculated by Mulliken population analysis with DFT/B3LYP with
6-311++G(d,p) basis set are listed in Table S2 (Supporting information). The Mulliken atomic
charge plot for MBBH is plotted in Figure S1 (Supporting information). From the results, C4
18

atom shows the higher negative charge due to the methoxy linkage. The C23 atom has high
positive charge due to the attachment of carbonyl group (C21=O22).
5. Conclusion
The FT-IR, FT-Raman and UV-Vis spectra of the Schiff base Compound (E)-N1-(4-
methoxybenzylidene)benzohydrazide have been recorded and analyzed. The detailed
interpretations of the vibrational spectra have been carried out. The optimized geometrical
parameters were calculated and compared with the reported XRD data. A complete vibrational
analysis has been carried out on the basis of quantum mechanical approach by DFT calculation.
The simulated spectra of MBBH are in agreement with recorded FT-IR and FT-Raman spectra.
The NBO analysis reflects the charge transfer occur within the molecule. The Lewis and non-
Lewis structure of MBBH shows that the contribution of ED of individual atoms, which leads the
molecular vibration with respect to hybridization of chemical bonds. HOMO and LUMO orbitals
have been visualized. The lowering of HOMO and LUMO energy gap supports the bioactivity
property of the molecule. In addition, mulliken charges, first order hyperpolarizabilities and
dipole moment of the title compound have also been calculated.
19

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24

Figure 1 The optimized molecular structure of MBBH

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
FT-IR/Exp
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
IR/B3LYP
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Figure 2 The combined experimental and theoretical IR spectra of MBBH

6
5
4
3
2
1
0
FT-Raman/Exp
7
6
5
4
3
2
1
0
Raman/B3LYP
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Figure 3 The combined experimental and theoretical Raman spectra of MBBH

Figure 4 The frontier molecular orbitals of MBBH

Figure 5 The molecular electrostatic potential of MBBH