This document discusses a study analyzing the molecular structure, vibrational spectra, and other properties of N-phenylbenzenesulfonamide (NPBS) using density functional theory calculations and experimental techniques. Key findings include: - NPBS was synthesized and its structure was optimized using DFT calculations. Experimental FTIR, FT-Raman, UV-Vis, and NMR spectra were also collected. - Potential energy scans revealed two stable conformers of NPBS depending on torsion angles between rings. Calculated bond lengths and angles matched experimental data well. - Vibrational band assignments were made by comparing experimental FTIR and FT-Raman spectra to spectra simulated using DFT. NBO

1. Synthesis, structural, spectral (FTIR, FT-Raman, UV, NMR), NBO and first
order hyperpolarizability analysis of N-phenylbenzenesulfonamide
by density functional theory
K. Govindarasu, E. Kavitha ⇑
, N. Sundaraganesan
Department of Physics (Engg.), Annamalai University, Annamalainagar 608 002, India
h i g h l i g h t s
The FTIR and FT-Raman spectra of
NPBS were reported.
The first order hyperpolarizability
was calculated.
UV–Vis spectra were recorded and
compared with calculated values.
Electronegativity and electrophilicity
index values also calculated.
g r a p h i c a l a b s t r a c t
Optimized molecular structure of N-phenylbenzenesulfonamide.
a r t i c l e i n f o
Article history:
Received 16 April 2014
Received in revised form 18 May 2014
Accepted 3 June 2014
Available online 14 June 2014
Keywords:
N-phenylbenzenesulfonamide
TD-DFT
NBO
UV–Vis
MEP
NMR
a b s t r a c t
In this study sulfonamide compound, N-phenylbenzenesulfonamide (NPBS) has been synthesized and
grown as a high quality single crystal by the slow evaporation solution growth technique. The grown
crystals were characterized by the Fourier transform infrared (4000–400 cmÀ1
), Fourier transform Raman
(3500–500 cmÀ1
), UV–Vis (200–800 nm) and NMR spectroscopy. Density functional (DFT) calculations
have been carried out for the compound NPBS by utilizing DFT level of theory using B3LYP/6-31G(d,p)
as basis set. The theoretical vibrational frequencies and optimized geometric parameters such as bond
lengths and bond angles have been calculated by using quantum chemical methods. The stability of
the molecule arising from hyper conjugative interaction and charge delocalization has been analyzed
using NBO analysis. The dipole moment, linear polarizability and first order hyperpolarizability values
were also computed. The chemical reactivity and ionization potential of NPBS were also calculated. In
addition, Molecular Electrostatic Potential (MEP), Frontier Molecular Orbital (FMO) analysis was investi-
gated using theoretical calculations. The thermodynamic properties of the compound were calculated at
different temperatures and corresponding relations between the properties and temperature were also
studied. Finally, geometric parameters, vibrational bands were compared with available experimental
data of the molecules.
Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.saa.2014.06.040
1386-1425/Published by Elsevier B.V.
⇑ Corresponding author. Tel.: +91 9442477462.
E-mail address: eswarankavitha@gmail.com (E. Kavitha).
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa

2. Introduction
Benzenesulfonamide derivatives are used as effective inhibitors
in the treatment of proliferative diseases as cancer, apoplexy, heart
failure, cystic fibrosis, hepatomegaly, etc. [1]. Benzenesulfonamide
moiety is an integral part of many drugs and drug-like scaffolds
[2,3]. The sulfonamide derivatives are known for their numerous
pharmacological activities, antibacterial, antitumor, insulin-release
stimulation and antithyroid properties [4]. In analytical area, sul-
fonamides have been investigated as reagents for the separation,
concentration, and selective determination of many of the first
row transition metal cations [5–7]. Because of the wide variety of
the biological importance of the sulfonamides, the synthesis of sev-
eral substituted sulfonamides, the study of their crystal structure
and other physical, chemical and biochemical studies have become
interesting field in research. The N-phenylbenzenesulfonamide
compound is one such organic compound that belongs to the sul-
fonamide family. There has been growing interest in using organic
materials for nonlinear optical (NLO) devices, functioning as sec-
ond harmonic generators, frequency converters, electro-optical
modulators, etc. The organic compound showing high hyperpolar-
izability are those containing an electron-donating group and an
electron withdrawing group interacting through a system of conju-
gated double bonds. In the case of sulfonamides, the electron with-
drawing group is the sulfonyl group [8,9].
Chandran et al. [10] studied FT-IR and computational study of
(E)-N-carbamimidoyl-4-((2-formylbenzylidene) amino) benzene
sulfonamide. Sarojini et al. [11] reported Synthesis, structural,
spectroscopic studies, NBO analysis, NLO and HOMO–LUMO of
4-methyl-N-(3-nitrophenyl) benzene sulfonamide with experi-
mental and theoretical approaches. Karabacak et al. [12] analyzed
theoretical investigation on the molecular structure, Infrared,
Raman and NMR spectra of para-halogen benzenesulfonamides,
4-X-C6H4SO2NH2 (X = Cl, Br or F). To best of our knowledge, there
is not any review summarizing the literature on the TD-DFT
frequency calculations of NPBS have been reported so far. The FTIR
and FT Raman spectroscopy combined with Quantum chemical
computations have been recently used as an effectively tool in
vibrational assignments of nonlinear optical molecule.
The present work mainly deals with detailed structural confor-
mation, experimental FT-IR and FT-Raman spectra, vibrational
assignments using total energy distribution (TED) and NLO activity
as well as DFT/B3LYP calculations for NPBS. Vibrational spectra of
NPBS have been analyzed on the basis of calculated TED. Theoreti-
cally computed vibrational wavenumbers were compared with
experimental values. The electron density (ED) in various bonding
and anti bonding orbital and E2 energies have been calculated by
Natural Bond Orbital (NBO) analysis using DFT method. The UV–
Vis spectroscopic studies along with HOMO–LUMO analysis have
been used to explain the charge transfer within the molecule. The
1
H and 13
C NMR chemical shifts were calculated within the gauge-
independent atomic orbital (GIAO) approach applying the same
method and the basis set as used for geometry optimization. The
1
H and 13
C NMR chemical shifts were converted to the TMS scale
by subtracting the calculated absolute chemical shielding of TMS
(d = R0–R, where d is the chemical shift, R is the absolute shielding
and R0 is the absolute shielding of TMS), whose value are 31.5 ppm
and 186.4 ppm, respectively. Chloroform was used as solvent.
Experimental
Synthesis
Aqueous solution of benzene sulfonylchloride (4.4 ml,
0.025 mol) was added 10 ml of 10% NaOH solution followed by
aniline (2.3 ml, 0.025 mol). The reaction mixture was taken in a
round bottom flask kept over a magnetic stirrer and stirrer well
for an hour. The solid separated out was washed with water and
dried over vacuum.
FT-IR, FT-Raman and UV–Vis spectral measurements
The FT-IR spectrum of N-phenylbenzenesulfonamide compound
was recorded in the range of 4000–400 cmÀ1
on a BRUKER Optik
GmbH FT-IR spectrometer using KBr pellet technique. The spec-
trum was recorded in the room temperature, with scanning speed
of 10 cmÀ1
, and spectral resolution: 4 cmÀ1
. FT-Raman spectrum of
the title compound was recorded using 1064 nm line of Nd:YAG
laser as excitation wavelength in the region 3500–50 cmÀ1
on a
BRUKER RFS 27: FT-Raman Spectrometer equipped with FT-Raman
molecule accessory. The spectral resolution was set to 2 cmÀ1
in
back scattering mode. The laser output was kept at 100 mW for
the solid sample. The ultraviolet absorption spectra of NPBS were
examined in the range 200–800 nm using Cary 500 UV–VIS–NIR
spectrometer. The UV pattern is taken from a 10 to 5 M solution
of NPBS, dissolved in ethanol solvent. The theoretically predicted
IR and Raman spectra at B3LYP/6-31G(d,p) level calculation along
with experimental FT-IR and FT-Raman spectra are shown in Figs.
1 and 2. The FTIR and UV–Vis spectral measurements were carried
out at Central Electro Chemical Research Institute (CECRI), Karaik-
udi and FT-Raman spectral measurement was carried out at Indian
Institute of Technology (IIT), Chennai.
Computational details
The density functional theory DFT/B3LYP with the 6-31G(d,p) as
basis set was adopted to calculate the properties of NPBS in the
present work. The entire calculations were performed using Gauss-
ian 03W program package [13]. The optimized geometry corre-
sponding to the minimum on the potential energy surface has
been obtained by solving self-consistent field equations. The equi-
librium geometry corresponding to the true minimum on the
Potential Energy Surface (PES) has been obtained by solving self
consistent field equation effectively. Furthermore, theoretical
vibrational spectra of the title compound were interpreted by
means of TED using the VEDA 4 program [14]. The Natural Bond
Orbital (NBO) calculations were performed using NBO 3.1 program
[15] as implemented in the Gaussian 03W [13] package at the DFT/
B3LYP level; in order to understand various second order interac-
tions between filled orbital of one subsystem and vacant orbital
of another subsystem, which is a measure of the intermolecular
delocalization or hyper conjugation. The first order hyperpolariz-
ability (b0) of this molecular system, and related properties (b, a0
and Da) of NPBS are calculated using HF/6-31G(d,p) basis set,
based on the finite-field approach [16]. UV–Vis spectra, electronic
transitions, vertical excitation energies, absorbance and oscillator
strengths were computed with the time-dependent DFT method.
The electronic properties such as HOMO and LUMO energies
were determined by TD-DFT approach. To investigate the reactive
sites of the title compound the MEP were evaluated using the
B3LYP/6-31G(d,p) method.
Prediction of Raman intensities
The Raman activities (Si) calculated by Gaussian 03 program
[13] has been converted to relative Raman intensities (IR
). The the-
oretical Raman intensity (IR
), which simulates the measured
Raman spectrum, is given by the equation [17,18]:
IR
i ¼ Cðm0 À miÞ4
mÀ1
i BÀ1
i Si ð1Þ
418 K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431

3. where Bi is a temperature factor which accounts for the intensity
contribution of excited vibrational states, and is represented by
the Boltzman distribution:
Bi ¼ 1 À ðexp Àhmic=kTÞ ð2Þ
In Eq. (1) m0 is the frequency of the laser excitation line (in this
work, we have used the excitation frequency m0 = 9398.5 cmÀ1
,
which corresponds to the wavelength of 1064 nm of a Nd:YAG
laser), mi is the frequency of normal mode (cmÀ1
), while Si is the
Raman scattering activity of the normal mode Qi. Ii
R
is given in arbi-
trary units (C is a constant equal 10À12
). In Eq. (2) h, k, c, and T are
Planck and Boltzman constants, speed of light and temperature in
Kelvin, respectively. Thus, the presented theoretical Raman inten-
sities have been computed assuming Bi equal 1. The theoretical
Raman spectra have been calculated by the Raint program [19].
The simulated spectra were plotted using a Lorentzian band shape
with a half-width at half-height (HWHH) of 3 cmÀ1
.
Results and discussion
Conformational stability
Potential energy surface are important because they aid us in
visualizing and describing the relationship between potential
energy and molecular geometry [20]. A potential energy surface
scan study with B3LYP/6-31G(d,p) method has been carried out
to understand the stability of planar and nonplanar structures of
the molecule. The profiles of potential energy surface for torsion
angle N10AS7AC1AC6 and C11AN10AS7AC1 are given in Fig. 3.
During the calculation; all the geometrical parameters are simulta-
neously relaxed while the N10AS7AC1AC6 and C11AN10AS7AC1
torsional angles are varied in steps of 10° up to 360°. Possible con-
formers of NPBS depend on the rotation of S7AN10 bond, linked to
phenyl ring A and B. The conformational energy profile shows two
maxima near 210° (À1031.75 Hartree) and 340° (À1028.7 Hartree)
and two local minima (stable conformers) observed at 0° or
360° (À1061.5 Hartree) and 280° (1066.78 Hartree) for
T(N10AS7AC1AC6). Similarly T(C11AN10AS7AC1) has one local
maxima near 280° (À1066.09 Hartree) and one local minima at
0° or 360° (À1067.17 Hatree). Further results are based on the
most stable conformer of NPBS molecule to clarify molecular struc-
ture and assignments of vibrational spectra.
Structural analysis
The optimized geometric parameters such as bond lengths,
bond angles and dihedral angles of the title molecule were given
in Table 1 using DFT calculation with 6-31G(d,p) as a basis set.
B3lyp/6-31G(d,p)
477
569
692
738
792
846
1045
1099
1199
1245
1291
1360
14531476
1591
3082
3436
4000 3500 3000 2500 2000 1500 1000 500
3785
3357
3101
2973
2918
2846
2754
2605
2542
2455
2366
2287
2144
1936
1859
1728
1639
1548
1442
1371
1246
1116
1041
968
858
808
713
623
445
Wavenumber (cm-1
)
IRintensity(arb.units)Transmittance(%)
B3lyp/6-31G (d,p)
Experimental
Fig. 1. Comparison of experimental and theoretical B3LYP/6-1G(d,p) FT-IR spectra for N-phenylbenzenesulfonamide.
K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431 419

4. The atom numbering scheme adopted in this study is given in
Fig. 4. Owing the absence of experimental data of the molecule
NPBS is compared with XRD data of closely related molecule
2-[(E)-(Dimethylamino)methyleneamino]-N-phenylbenzenesul-
fonamide [21]. Our title molecule contains two phenyl rings and
sulfonyl group is substituted to atom C1 of the phenyl ring A and
amide group is substituted to atom C11 of the phenyl ring B. In
the benzene ring, CAC bond length is about 1.396 Å [22]. The cal-
culated CAC bond length in phenyl ring varies from 1.394 to
1.463 Å by DFT method which is good agreement with experimen-
tal data (1.382–1.410 Å). In our case the CAC bonds in phenyl rings
are not of the same bond length. Due to NH substitution of phenyl
ring B appears a little distorted, the bond length C11AC12 =
1.401 Å and C11AC16 = 1.402 Å which is longer than C12AC13 =
1.394 Å and C14AC15 = 1.397 Å by DFT method at the rest of the
substitution. CAH bond lengths are presented as nearly equal val-
ues which is varies from 1.083 to 1.087 Å by DFT method, which is
nearly coincide with experimental findings at 0.950 Å. The bond
length of sulfonyl group is S7AO8 = 1.463 Å and S7AO9 = 1.462 Å
by DFT method, these bond lengths are very close to experimental
values 1.429 Å and 1.433 Å respectively. The NAH bond distance is
1.015 Å which is slightly (0.155 Å) greater than the experimental
value 0.86 Å. From the theoretical values, it is found that most of
the optimized bond lengths are slightly larger than the experimen-
tal values due to fact that the theoretical calculations belong to
isolated molecules in gaseous phase and the experimental results
belong to molecules in solid state.
The benzene ring A appears to be a little distorted because of
the SO2 group substitution as seen from the bond angles
C2AC1AC6, which are calculated as (121.5°) by DFT method which
is greater than typical hexagonal angle of (120°). With the electron
donating substituents on the benzene ring, the symmetry of the
ring is distorted, yielding ring angles smaller than (120°) at the
point of substitution [23]. Similarly due to NH substitution of phe-
nyl ring B appears a little distorted, the bond angles
C12AC11AC16 = 119.8° by DFT method 119.9° by experimental
value, which is smaller than typical hexagonal angle of (120°).
The bond angle of sulfonyl group is O8AS7AO9 = 122.7° by DFT
method.
The N10AC11 bonds in the C1AS7O9AN10H22AC11 segments
have gauche torsions with respect to the S7@O9 bonds. The mole-
cules are twisted at the S7 atom with the C1AS7AN10AC11 torsion
angles of 60.49° by DFT method which is closer to experimental
value 65.09°. The sulfonyl and the aniline benzene ring (ring B)
title molecule was tilted relative to each other by
T(S7AN10AC11AC16) = 57.53° by DFT method which is nearly
coincide with experimental value 61.15°. Similarly the dihedral
angle between sulfonyl and benzene ring A is
C6AC1AS7AN10 = 92.21° by DFT method, this is largely (39.04°)
deviate from the experimental value at 53.17°. The discrepancies
38
108
208
292
446
523
607
730
792
846
976
1099
116111991245
1591
3082
4000 3500 3000 2500 2000 1500 1000 500 0
3212
3073
2949
2890
2757
2625
25502531
2454
2361
2311
2244
2184
2111
1983
1696
1584
1476
14141405
1279
1220
1156
1090
1000
928
838
720
614
556
475
417
329
280
221
86
wavenumber (cm-1
)
Ramanintensity(arb.units)
B3lyp/6-31G (d,p)
Experimental
Fig. 2. Comparison of experimental and theoretical B3LYP/6-31G(d,p) FT-Raman spectra for N-phenylbenzenesulfonamide.
420 K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431

5. between the calculated geometrical parameters and XRD results are
due to the fact that the comparison made between the experimental
data, obtained from single crystal, and the calculated results are for
isolated molecule in the gaseous phase.
Vibrational assignments
In order to have a full understanding of the spectral properties
of these nonlinear optical systems, we performed a detailed analy-
sis of Vibrational circular dichorism exhibited by these nonlinear
active molecules. The assignment of skeletal vibrational modes
and functional group vibrations in the IR and Raman region are
summarized in Table 2. The total number of bands in Raman and
IR spectra is fewer than 3nÀ6 because some vibrations are too
low intensity to be detected in the range shown. The title molecule
consists of 27 atoms, which undergo 75 normal modes of vibra-
tions. It agrees with C1 point group symmetry, all vibrations are
active both in Raman and infrared absorption. The unscaled
B3LYP/6-31G(d,p) vibrational frequencies are generally larger than
the experimental value. This is partly due to the neglect of
anharmonicity and partly due to approximate nature of the quan-
tum mechanical methods. The calculated vibrational frequencies
were scaled in order to improve the agreement with the experi-
ment values. In our study we have followed scaling factor of
0.9608 for B3LYP/6-31G(d,p). After scaling with a scaling factor
[24], the deviation from the experiments is less than 10 cmÀ1
with
few exceptions. It is convenient to discuss the vibrational spectra
of NPBS in terms of characteristic spectral regions as described
below.
CAC vibrations
The bands between 1400 and 1650 cmÀ1
in the aromatic and
hetero aromatic compounds are assigned to carbon vibrations
[25]. Varsanyi [26] observed these bands are of variable intensity
at 1625–1280 cmÀ1
. In the present study CAC stretching vibrations
observed at 1548, 1371, 1246 and 1159 cmÀ1
in FT-IR spectrum
and 1370, 1256 and 1058 cmÀ1
in FT-Raman spectrum. The calcu-
lated wavenumbers at 1577, 1576, 1363, 1313, 1309, 1294, 1245,
1158, 1144, 1141, 1067 and 1063 cmÀ1
were assigned CAC
stretching vibrations by DFT method also correlated with the
0 50 100 150 200 250 300 350 400
-1070
-1065
-1060
-1055
-1050
-1045
-1040
-1035
-1030
-1025
Relativeenergy(Hartree)
N10-S7-C1-C6 Dihedral angle (°)
0 50 100 150 200 250 300 350 400
-1067.4
-1067.2
-1067.0
-1066.8
-1066.6
-1066.4
-1066.2
-1066.0
Relativeenergy(Hartree)
C11-N10-S7-C1 Dihedral angle (°)
Fig. 3. Dihedral angle-relative energy curves of N phenylbenzenesulfonamide by B3LYP/6-31G(d,p) level of theory.
K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431 421

6. experimental observations. The in-plane deformation vibration is
at higher frequencies than the out-of plane vibrations. Shimanou-
chi et al. [27] gave the frequency data for these vibrations for dif-
ferent benzene derivatives as a result of normal coordinate
analysis. Sarojini et al. [11] find out the wavenumbers for CACAC
in plane bending vibrations experimentally at 991, 818 and
665 cmÀ1
in FT-IR spectrum and 1015, 815, 351 and 315 cmÀ1
in
FT-Raman spectrum and theoretically computed wavenumbers at
1475, 992, 796, 623, 392 and 303 cmÀ1
by DFT method. In our case
CACAC in plane bending vibrations observed at 1483, 1016, 858
and 557 cmÀ1
in FT-IR spectrum and 1476, 838, 791 and
614 cmÀ1
in FT-Raman spectrum. The computed wavenumbers at
Table 1
Calculated optimized parameter values of the N-phenylbenzenesulfonamide (bond length in (Å), angles in (°)).
Bond length B3LYP Expa
Bond angle B3LYP Expa
Dihedral angle B3LYP Expa
C1AC2 1.397 1.391 C2AC1AC6 121.5 121.8 C6AC1AC2AC3 À0.56
C1AC6 1.397 1.410 C2AC1AS7 119.4 118.5 C6AC1AC2AH17 178.41
C1AS7 1.797 1.765 C6AC1AS7 119.0 119.6 S7AC1AC2AC3 178.53
C2AC3 1.395 1.382 C1AC2AC3 118.9 120.1 S7AC1AC2AH17 À2.51
C2AH17 1.084 0.950 C1AC2AH17 119.9 119.9 C2AC1AC6AC5 0.35
C3AC4 1.396 1.390 C3AC2AH17 121.2 119.9 C2AC1AC6AH21 À178.25
C3AH18 1.086 0.950 C2AC3AC4 120.2 119.2 S7AC1AC6AC5 À178.74 À179.51
C4AC5 1.397 1.384 C2AC3AH18 119.6 120.4 S7AC1AC6AH21 2.66
C4AH19 1.086 0.950 C4AC3AH18 120.2 120.4 C2AC1AS7AO8 162.09
C5AC6 1.394 1.403 C3AC4AC5 120.3 120.7 C2AC1AS7AO9 27.86
C5AH20 1.086 0.950 C3AC4AH19 119.8 119.7 C2AC1AS7AN10 À86.90
C6AH21 1.085 0.950 C5AC4AH19 119.8 119.7 C6AC1AS7AO8 À18.80
S7AO8 1.463 1.429 C4AC5AC6 120.1 121.5 C6AC1AS7AO9 À153.04
S7AO9 1.462 1.433 C4AC5AH20 120.2 119.2 C6AC1AS7AN10 92.21 53.17
S7AN10 1.701 1.645 C6AC5AH20 119.7 119.2 C1AC2AC3AC4 0.28
N10AC11 1.423 1.436 C1AC6AC5 119.0 116.5 C1AC2AC3AH18 179.81
N10AH22 1.015 0.86 C1AC6AH21 119.8 – H17AC2AC3AC4 À178.68
C11AC12 1.401 1.393 C5AC6AH21 121.3 – H17AC2AC3AH18 0.86
C11AC16 1.402 1.390 C1AS7AO8 108.0 109.2 C2AC3AC4AC5 0.21
C12AC13 1.394 1.382 C1AS7AO9 107.5 107.8 C2AC3CA4AH19 179.71
C12AH23 1.087 0.950 C1AS7AN10 106.8 106.0 H18AC3AC4AC5 À179.33
C13AC14 1.395 1.390 O8AS7AO9 122.7 118.9 H18AC3AC4AH19 0.18
C13AH24 1.086 0.950 O8AS7AN10 103.7 105.6 C3AC4AC5AC6 À0.42
C14AC15 1.397 1.385 O9AS7AN10 107.2 108.7 C3AC4AC5AH20 179.10
C14AH25 1.086 0.950 S7AN10AC11 123.5 121.3 H19AC4AC5AC6 À179.93
C15AC16 1.394 1.384 S7AN10AH22 109.0 106.4 H19AC4AC5AH20 À0.41
C15AH26 1.086 0.950 C11AN10AH22 115.0 110.7 C4AC5AC6AC1 0.14
C16AH27 1.083 0.950 N10AC11AC12 119.5 118.8 C4AC5AC6AH21 178.72
N10AC11AC16 120.6 121.1 H20AC5AC6AC1 À179.38
C12AC11AC16 119.8 119.9 H20AC5AC6AH21 À0.80
C11AC12AC13 120.1 119.9 C1AS7AN10AC11 60.49 65.09
C11AC12AH23 119.7 120.1 C1AS7AN10AH22 À79.27
C13AC12AH23 120.2 120.1 O8AS7AN10AC11 174.45
C12AC13AC14 120.3 120.3 O8AS7AN10AH22 34.68
C12AC13AH24 119.5 119.8 O9AS7AN10AC11 À54.50
C14AC13AH24 120.3 119.8 O9AS7AN10AH22 165.74
C13AC14AC15 119.5 119.4 S7AN10AC11AC12 À125.22 À122.99
C13AC14AH25 120.2 120.3 S7AN10AC11AC16 57.53 61.15
C15AC14AH25 120.3 120.3 H22AN10AC11AC12 12.43
C14AC15AC16 120.8 120.9 H22AN10AC11AC16 À164.82
C14AC15AH26 120.0 119.6 N10AC11AC12AC13 À176.80
C16AC15AH26 119.2 119.6 N10AC11AC13AH23 3.03
C11AC16AC15 119.5 119.5 C16AC11AC12AC13 0.47
C11AC16AH27 119.4 120.3 C16AC11AC12AH23 À179.69
C15AC16AH27 121.1 120.3 N10AC11AC16AC15 178.22
N10AC11AC16AH27 À1.55
C12AC11AC16AC15 0.98
C12AC11AC16AH27 À178.79
C11AC12AC13AC14 À1.41
C11AC12AC13AH24 179.35
H23AC12AC13AH24 178.76
H23AC12AC13AH24 À0.48
C12AC13AC14AC15 0.88
C12AC13AC14AH25 À179.49
H24AC13AC14AC15 À179.89
H24AC13AC14AH25 À0.26
C13AC14AC15AC16 0.59
C13AC14AC15AH26 179.28
H25AC14AC15AH26 À179.04
H25AC14AC15AH26 À0.35
C14AC15AC16AC11 À1.51
C14AC15AC16AH27 178.25
H26AC15AC16AC11 179.78
H26AC15AC16AH27 À0.45
a
Taken from Ref. [21].
422 K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431

7. 1477, 1015, 976, 974, 946, 843, 790, 608, 607, 602 and 567 cmÀ1
by
DFT method assigned as CACAC in plane bending vibrations. The
recorded and computed wavenumber for the CACAC in plane
bending vibrations vibration are in good agreement with above lit-
erature data. The CACACAC out of plane bending vibrations
observed at 557 and 445 cmÀ1
in FT-IR spectrum and 928 and
329 cmÀ1
in FT-Raman spectrum. The calculated wavenumbers at
933, 678, 567, 446, 405 and 332 cmÀ1
assigned as CACACAC out
of plane bending vibrations. The mode no’s 59, 63, 67, 69 and 71
were identified as CACACAC torsional deformation s(CCCC) modes
these are shown in Table 2.
CAH vibrations
The aromatic structures shows the presence of CAH stretching
vibrations in the region 3100–3000 cmÀ1
which is the characteris-
tic region for the ready identification of CAH stretching vibrations.
In this region, the bands are not affected appreciably by the nature
of substituents [28,29]. In our case CAH stretching vibrations
observed at 3101 and 3070 cmÀ1
in FT-IR and 3150 and
3073 cmÀ1
in FT-Raman spectrum. The calculated wavenumbers
at the range 3111–3051 cmÀ1
(mode no’s: 2–11) assigned CAH
stretching vibrations, which is good agreement with experimental
values and TED contributes almost above 80%. The CAH in-plane
bending vibration is usually expected to occur in the region
1300–1000 cmÀ1
and these vibrations are very useful for charac-
terization purpose [30]. In our title molecule CAH in-plane bending
vibrations observed at 1319, 1246, 1159 and 1016 cmÀ1
in FT-IR
and 1279, 1256, 1191,1058 and 1000 cmÀ1
in FT-Raman spectrum.
Theoretically predicted wavenumbers at 1313, 1286, 1245, 1198,
1158, 1063, 1015 and 1007 cmÀ1
by DFT method assigned CAH
in-plane bending vibrations. The CAH out-of-plane bending vibra-
tions are strongly coupled vibrations and occur in the region 1000–
750 cmÀ1
[31]. In this work, the out-of-plane bending vibrations
were recorded at 968 and 806 cmÀ1
in FT-IR and at 928 and
880 cmÀ1
in FT-Raman spectrum. The computed wavenumbers at
970, 933, 882 and 813 cmÀ1
were identified CH out-of-plane bend-
ing vibrations which is good agreement with experimental obser-
vations. The TED contributes for these modes (mod no’s: 39, 42,
44 47) almost above 70%.
SO2 vibrations
The symmetric and asymmetric SO2 stretching vibrations occur
in the region 1125–1150 and 1295–1330 cmÀ1
[32–34] respec-
tively. In the title molecule, the S@O symmetric stretching vibration
is observed at 1088 cmÀ1
in FT-IR spectrum and at 1090 cmÀ1
in FT-
Raman spectrum and calculated wavenumber at 1098 cmÀ1
by DFT
method which is evident from the Table 2 TED contributes 80%
(mode no: 31). The computed wavenumber at 1294 cmÀ1
assigned
S@O asymmetric stretching vibration, TED contributes 43% for
this mode (mode no: 23). The region of the SO2 scissors
(560 ± 40 cmÀ1
) and that of SO2 wagging vibration
(500 ± 55 cmÀ1
) partly overlap, the two vibrations appear sepa-
rately [35]. In our present work the frequency at 510 cmÀ1
in
FT-Raman spectrum and at 557 cmÀ1
in FT-IR spectrum were iden-
tified SO2 scissoring and wagging vibration respectively. The com-
puted wavenumbers for these modes (mode no’s: 59 and 57) are
507 and 567 cmÀ1
by DFT method assigned SO2 scissoring and wag-
ging vibration respectively. The SO2 rocking mode identified at
around 350 cmÀ1
[35]. For the title compound, the DFT calculation
give this mode (mode no: 67) at 274 cmÀ1
.
CAS, SAN and NAC vibrations
Normally the CAS stretching bands are usually falls in the range
930–670 cmÀ1
[9] with a moderate intensity. In our present study
the computed wavenumber at 672 cmÀ1
(mode. no: 53) assigned
CAS stretching vibration. The CAS in-plane and out-of-plane bend-
ing vibrations bands are expected in the regions 600–420 cmÀ1
and
420–320 cmÀ1
, respectively [12]. In our NPBS molecule the calcu-
lated frequency at 602 and 391 cmÀ1
by DFT method gives the
CAS in-plane (dCSN) and out-of-plane (cCSNC) bending vibrations
respectively. The SAN stretching vibration is expected in the region
905 ± 30 cmÀ1
[12]. The band observed at 858 cmÀ1
in FT-IR and
838 cmÀ1
in FT-Raman spectrum and calculated at 843 cmÀ1
by
DFT method is identified as SN stretching mode (mode no: 45)
for our title molecule. Because of the mixing of several bands,
the identification of CAN vibrations is a very difficult task. Shan-
mugam and Sathyanarayana [36] assigned CAN stretching absorp-
tion in the region 1382–1266 cmÀ1
. In our present work CAN
stretching vibration observed at 1191 cmÀ1
in FT-Raman spectra
and predicted at 1198 cmÀ1
by DFT method shows good agree-
ment. The band at 475 and 329 cmÀ1
in FT-Raman spectrum and
computed frequency at 478 and 332 cmÀ1
by DFT method is iden-
tified as CCN in plane bending vibrations.
NAH vibrations
In heterocyclic molecules, the NAH stretching vibrations have
been measured in region 3500–3000 cmÀ1
[37]. In our NPBS mole-
cule NAH stretching vibrations observed at 3213 cmÀ1
in FT-IR
spectrum and at 3212 cmÀ1
in FT-Raman spectrum. The computed
wavenumber at 3433 cmÀ1
by DFT method assigned as NAH
stretching vibration. It is a pure mode TED contributes exactly at
100%. The observed FT-IR frequency (3213 cmÀ1
) and FT-Raman
frequency (3212 cmÀ1
) is deviate (287 cmÀ1
) and (286 cmÀ1
) from
expected range 3500–3000 cmÀ1
respectively. This may be due to
inter molecular interactions of the molecule in solid state. The
NAH in-plane bending vibration is expected near 1400 cmÀ1
. In
our present case the band at 1442 cmÀ1
in FT-IR and 1584 cmÀ1
in FT-Raman and computed wavenumber at 1452 and 1580 cmÀ1
by DFT method were identified as NH in plane bending modes.
The mode numbers 58 and 60 having the frequency at 475 cmÀ1
in FT-Raman spectra and calculated wavenumbers at 524 and
478 cmÀ1
by DFT method assigned NH out-of plane bending vibra-
tions. The calculated wavenumber at 478 cmÀ1
correlate well with
experimental Raman spectrum at 475 cmÀ1
.
NBO analysis
Natural bond orbital analysis provides an efficient method for
studying intra-and intermolecular bonding and interaction among
bonds, and also provides a convenient basis for investigating
charge transfer or conjugative interaction in molecular systems
[38]. The NBO analysis is carried out by examining all possible
Fig. 4. Optimized molecular structure and atomic numbering of N-
phenylbenzenesulfonamide.
K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431 423

8. Table 2
Comparison of the experimental and calculated vibrational spectra and proposed assignments of N-phenylbenzenesulfonamide.
Mode nos. Experimental wavenumbers (cmÀ1
) Theoritical wavenumbers (cmÀ1
) TED (P10%) with assignments
B3LYP/6-31G(d,p)
FT-IR FT-Raman Unscaled Scaled IIR
a
IRA
b
1 3213 3212 3573 3433 28.43 0.63 tNH(100)
2 3150 3238 3111 0.70 0.83 tCH(82)RingB
3 3101 3232 3105 1.88 0.92 tCH(88)RingA
4 3223 3097 4.15 1.46 tCH(89)RingA
5 3210 3083 17.52 3.81 tCH(86)RingAB
6 3209 3084 14.83 1.29 tCH(82)RingAB
7 3073 3200 3075 11.70 1.44 tCH(81)RingA
8 3070 3197 3071 22.53 1.01 tCH(68)RingB
9 3189 3064 0.55 0.73 tCH(95)RingA
10 3187 3062 0.86 1.28 tCH(77)RingB
11 3175 3051 7.91 0.48 tCH(80)RingB
12 1595 1657 1592 31.31 5.06 tCC(53)RB + dHCC(18)RB
13 1584 1644 1580 3.88 0.27 dHNC(42)
14 1642 1577 1.18 1.89 tCC(50)RA + dHCC(20)RA
15 1548 1640 1576 0.40 0.95 tCC(54)RA + dHCC(14)RA
16 1483 1476 1537 1477 54.49 0.59 dHCC(61)RB + dCCC(12)RB
17 1519 1460 4.45 0.08 dHCC(58)RA
18 1442 1511 1452 16.92 0.34 dHCC(40)RB + dHNC
19 1412 1414 1487 1429 18.02 0.10 dHCC(53)RA
20 1371 1370 1418 1363 75.53 1.43 tCC(14)RB + dHNS(49)
21 1319 1367 1313 5.90 0.14 tCC(18)RAB + dHCC(39)RAB
22 1362 1309 0.31 0.26 tCC(25)RAB + dHCC(13)RAB
23 1346 1294 86.53 0.26 tCC(33)RAB + tSOasym(43)
24 1279 1338 1286 0.10 0.01 dHCC(52)
25 1246 1256 1296 1245 45.30 4.02 tCC(33)RB + dHCC(14)RB + dHNS(15)
26 1191 1247 1198 38.24 5.77 tNC(25) + dHCC(10)RB + dHNS(11)
27 1204 1157 2.07 1.38 dHCC(68)RAB
28 1159 1205 1158 1.15 0.60 tCC(13)RAB + dHCC(73)RAB
29 1190 1144 0.04 0.61 tCC(13)RA + dHCC(76)RA
30 1188 1141 0.27 0.70 tCC(14)RB + dHCC(73)RB
31 1088 1090 1143 1098 206.04 3.12 tSOsym(80)
32 1111 1067 8.29 0.08 tCC(13)RB + dHCC(32)RB
33 1058 1107 1063 5.47 0.04 tCC(14)RA + dHCC(34)RA
34 1041 1087 1045 56.74 1.20 tSC+ dHCC RA
35 1016 1056 1015 6.09 2.05 dHCC(16)RB + dCCC(12)RB
36 1000 1048 1007 3.27 2.49 dHCC(19)RA + dCCC(16)RA
37 1015 976 0.12 2.92 dCCC(26)RA + dCCC(43)RB
38 1014 974 2.86 4.42 dCCC(48)RA + dCCC(23)RB
39 968 1010 970 0.11 0.19 cHCCC(77)RA
40 961 998 958 1.37 0.09 sHCCH(72)RB
41 985 946 0.02 0.04 dCCC(19)RA + sHCCS(26)
42 928 971 933 1.82 0.04 sHCCS(15) + cHCCC(75)RB + cCCCC(10)RB
43 916 944 907 0.30 0.17 sHCCCS(75)
44 880 918 882 14.21 0.67 cHCCC(77)RB
45 858 838 877 843 90.54 4.17 dCCC(12)RB + tSN(34)
46 829 861 828 0.56 0.44 sHCCS(92)RA
47 806 846 813 2.31 1.28 cHCCC(88)RB
48 791 822 790 38.71 2.94 dCCC(15)RB + dCNS(10)
49 748 768 738 18.16 0.41 sHCCS(60) + cSCCC(24)
50 713 720 761 731 31.60 2.56 sHCCS(51)
51 688 722 693 79.92 1.24 dCCC(15)RA + sHCCS(13)
52 706 678 19.87 0.34 cCCCC(74)
53 699 672 20.96 0.03 tSC(51) + dCCC(12)RA + cCCCC(13)
54 614 633 608 53.77 4.16 dCCC(38)RB
55 631 607 16.76 1.35 dCCC(74)RB
56 626 602 5.88 2.10 dCCC(47)RA + dCSN(12) + dCCS(27)
57 557 590 567 182.92 2.67 dCCC(11)RAB + cCCCC(37)RAB + dOSO wagg
58 545 524 48.49 1.89 dCNS(12) + cNCSH(38) + cHNCC(33)
59 510 527 507 21.78 1.17 dOSO sci(58) + sCCCC(29)RB
60 475 497 478 43.65 1.32 dCCN(19) + cNCSH(21) + cHNCC(20)
61 445 465 446 3.99 1.38 cCCCC(29)RA
62 421 405 0.73 0.13 cCCCC(80)RB
63 414 398 0.01 0.05 sHCCS(15) + sCCCC(76)RA
64 407 391 1.15 0.99 cCSNC(45)
65 329 346 332 3.79 2.31 dCCN(13) + cCCCC(35)RB
66 280 307 295 3.19 3.87 tSC(48) + dCSN(10)
67 285 274 0.53 2.65 dOSO Rock(11) + sCCCC(15)RB
68 255 274 263 0.44 1.06 dCNS(58)
69 215 206 0.29 6.01 sCCCC(61)RAB
70 190 184 177 1.31 0.79 dCSN(31) + sCSNC(14)
71 124 119 4.12 2.39 dCCN(10) + dCNS(13) + sCCCC(14)RB + sCSNC(13)
424 K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431

9. interactions between ‘filled’ (donor) Lewis-type NBOs and ‘empty’
(acceptor) nonLewis NBOs, and estimating their energy by 2nd
order perturbation theory. The localized orbitals in the best Lewis
structure can interact strongly. A filled bonding or lone pair orbital
can act as a donor and an empty or filled bonding, anti-bonding or
lone pair orbital can act as an acceptor. These interactions can
strengthen and weaken bonds. A lone pair donor ? anti-bonding
acceptor orbital interaction will weaken the bond associated with
the anti-bonding orbital. Conversely, an interaction with a bonding
pair as the acceptor will strengthen the bond [39]. The second-
order Fock-matrix was carried out to evaluate the donor–acceptor
interactions in the NBO basis. The output obtained by the
2nd-order perturbation theory analysis is normally the first to be
examined by the experienced NBO user in searching for significant
delocalization effects. However, the strengths of these delocaliza-
tion interactions, E(2), are estimated by second order perturbation
theory as estimated by the following equation.
E2 ¼ DEij ¼ qi
Fði; jÞ
2
ej À ei
qi is the donor orbital occupancy; Ei, Ej is the diagonal elements and
Fij is the off diagonal NBO Fock matrix element.
The larger E(2), value the more intensive is the interaction
between electron donors and acceptor, i.e. the more donation ten-
dency from electron donors to electron acceptors and the greater
the extent of conjugation of the whole system. The intramolecular
interaction are formed by the orbital overlap between r(CAC) and
rÃ
(CAC); p(CAC) and pÃ
(CAC) and LP(1) and LP(2) bond orbital
which results intramolecular charge transfer (ICT) causing stabil-
ization of the system. In our molecule, the p electron delocalization
is maximum around C1AC2, C3AC4 and C5AC6 distributed to pÃ
antibonding of C3AC4, C5AC6, C1AC2 and C5AC6 with a stabiliza-
tion energy of about 20.96, 23.85, 19.21, 19.25 and 20.84 kJ/mol as
shown in Table 3. Another hyper-conjugative interaction of
p(C12AC13) ? LP (1) C11, LPÃ
(1) C14 and p (C15AC16) ? LP (1)
C11, LPÃ
(1) C14 which increases ED(1.024, 1.011, 1.024 and
1.011e) that weakens the respective bonds leading to stabilization
of 53.53, 44.50, 55.54 and 47.45 kJ/mol respectively. pÃ
(C1AC2) of
the NBO conjugated with pÃ
(C3AC4) and pÃ
(C5AC6) leads to an
enormous stabilization of 226.29 and 210.33 kJ/mol respectively.
This strong stabilization denotes the larger delocalization. This
highest interaction around the ring can induce the large bioactivity
in the compound. The maximum electron density of 1.846e occurs
in the intramolecular hyperconjugative interaction of the LP (1)
N10 conjugate with orbital of LP (1) C11 which leads to strong
Table 2 (continued)
Mode nos. Experimental wavenumbers (cmÀ1
) Theoritical wavenumbers (cmÀ1
) TED (P10%) with assignments
B3LYP/6-31G(d,p)
FT-IR FT-Raman Unscaled Scaled IIR
a
IRA
b
72 109 105 0.88 9.61 sCSNC(50)
73 41 39 0.07 29.84 dCCS(18) + sCCSN(78)
74 33 32 0.55 70.45 sCSNC(65)
75 26 25 0.11 100.00 Lattice vibration
m – stretching; d in-plane bending; c – out-of-plane bending; s – torsion; w – weak; s – strong; vs – very strong; vw – very weak.
a
IIR – IR Intensity (Km molÀ1
).
b
IRa – Raman intensity (Arb units) (intensity normalized to 100%); RA – Ring A; RB – Ring B.
Table 3
Second order perturbation theory analysis of Fock Matrix in NBO basis for N-phenylbenzenesulfonamide.
Donor (i) ED (i)(e) Acceptor (j) ED (j)(e) E(2)a
(kJ molÀ1
) E(j)–E(i)b
(a.u.) F(i,j)c
(a.u.)
p(C1AC2) 1.680 pÃ
(C3AC4) 0.317 17.03 0.29 0.063
pÃ
(C5AC6) 0.308 20.96 0.29 0.070
p(C3AC4) 1.645 pÃ
(C1AC2) 0.385 23.85 0.27 0.072
pÃ
(C5AC6) 0.308 19.21 0.28 0.066
p(C5AC6) 1.650 pÃ
(C1AC2) 0.385 19.25 0.27 0.065
pÃ
(C3AC4) 0.317 20.84 0.28 0.069
p(C12AC13) 1.684 LP (1) C11 1.024 53.53 0.13 0.093
LPÃ
(1) C14 1.011 44.50 0.15 0.089
p(C15AC16) 1.670 LP (1) C11 1.024 55.54 0.13 0.092
LPÃ
(1) C14 1.011 47.45 0.14 0.090
LP (2) O8 1.815 rÃ
(C1AS7) 0.211 18.11 0.45 0.081
LP (3) O8 1.783 rÃ
(S7AO9) 0.155 19.23 0.57 0.095
rÃ
(S7AN10) 0.268 15.55 0.41 0.072
LP(2)O9 1.819 rÃ
(C1AS7) 0.211 17.74 0.45 0.080
rÃ
(S7AN10) 0.268 10.24 0.41 0.059
LP(1)N10 1.846 LP(1)C11 1.024 25.74 0.19 0.084
LP(1)C11 1.024 pÃ
(C12AC13) 0.342 61.48 0.15 0.104
pÃ
(C15AC16) 0.321 58.18 0.16 0.104
LPÃ
(1)C11 1.010 pÃ
(C12AC13) 0.342 71.60 0.14 0.107
pÃ
(C15AC16) 0.321 65.98 0.14 0.106
pÃ
(C1AC2) 0.384 pÃ
(C3AC4) 0.317 226.29 0.01 0.084
pÃ
(C5AC6) 0.308 210.33 0.01 0.078
rÃ
(S7AO9) 0.154 rÃ
(C1AC6) 0.023 0.68 0.27 0.040
rÃ
(S7AO8) 0.145 rÃ
(N10AC11) 0.031 1.55 0.11 0.040
ED means electron density.
a
E(2) means energy of hyper conjugative interactions.
b
Energy difference between donor and acceptor i and j NBO orbitals.
c
F(i, j) is the Fock matrix element between i and j NBO orbitals.
K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431 425

10. charge delocalization with 25.74 kJ/mol of energetic contribution.
The magnitude of charges transferred from LP (3) O8 ?
rÃ
(S7AO9), LPÃ
(1) C11 ? pÃ
(C12AC13) and rÃ
(S7AO8) ?
rÃ
(N10AC11) show that stabilization energy of about 19.23,
61.48 and 1.55 kJ/mol respectively.
Static polarizability and first order hyperpolarizability
The static polarizability (a) and the hyper polarizability (b) and
the electric dipole moment (l) of the N-phenylbenzenesulfonam-
ide are calculated by finite field method using B3LYP/6-31G(d,p)
basis set. To calculate all the electric dipole moments and the first
hyper polarizabilities for the isolated molecule, the origin of the
Cartesian coordinate system (x, y, z) = (0, 0, 0) was chosen at own
center of mass of NPBS. The NLO activity provide the key functions
for frequency shifting, optical modulation, optical switching and
optical logic for the developing technologies in areas such as com-
munication, signal processing and optical interconnections [40,41].
The first static hyperpolarizability (bo) and its related properties (b,
ao and Da) have been calculated using B3LYP/6-31G(d,p) level
based on finite field approach. In the presence of an applied electric
field, the energy of a system is a function of the electric field and
the first hyperpolarizability is a third rank tensor that can be
described by a 3 Â 3 Â 3 matrix. The 27 components of the 3D
matrix can be reduced to 10 components because of the Kleinman
symmetry [42]. The matrix can be given in the lower tetrahedral
format. It is obvious that the lower part of the 3 Â 3 Â 3 matrices
is a tetrahedral. The components of b are defined as the coefficients
in the Taylor series expansion of the energy in the external electric
field. When the external electric field is weak and homogeneous,
this expansion is given below:
E ¼ Eo
À laFa À 1=2aabFaFb À 1=6babcFaFbFc þ Á Á Á
where Eo
is the energy of the unperturbed molecules, Fa is the field
at the origin, la, aab and babc are the components of dipole moment,
polarizability and first hyperpolarizability, respectively.
The total static dipole moment l, the mean polarizability ao, the
anisotropy of the polarizability Da and the mean first hyperpolar-
izability bo, using the x, y and z components are defined as:
Dipole moment is
l ¼ ðl2
x þ l2
y þ l2
z Þ
1=2
Static polarizability is
a0 ¼ ðaxx þ ayy þ azzÞ=3
Total polarizability is
Da ¼ 2À1=2
½ðaxx À ayyÞ2
þ ðayy À azzÞ2
þ ðazz À axxÞ2
þ 6a2
xzŠ
1=2
First order hyperpolarizability is
b ¼ ðb2
x þ b2
y þ b2
z Þ
1=2
where
bx ¼ ðbxxx þbxyy þbxzzÞ
by ¼ ðbyyy þbyzz þbyxxÞ
bz ¼ ðbzzz þbzxx þbzyyÞ
b ¼ ½ðbxxx þbxyy þbxzzÞ2
þðbyyy þbyzz þbyxxÞ2
þðbzzz þbzxx þbzyyÞ2
Š
1=2
Since the values of the polarizabilities (a) and hyperpolarizabil-
ity (b) of the Gaussian 03 output are reported in atomic units (a.u.),
the calculated values have been converted into electrostatic
units (esu) (For a: 1 a.u. = 0.1482 Â 10À24
esu; For b: 1 a.u. =
8.639 Â 10À33
esu). The mean polarizability ao and total polariz-
ability Da of our title molecule are 20.0631 Â 10À24
esu and
5.4236 Â 10À24
esu respectively. The total molecular dipole
moment and first order hyperpolarizability are 2.6333 Debye and
1.8172 Â 10À30
esu, respectively and are depicted in Table 4. Total
dipole moment of NPBS molecule is approximately two times
greater than that of urea and first order hyperpolarizability is 5
times greater than that of urea (l and b of urea are 1.3732 Debye
and 0.3728 Â 10À30
esu obtained by HF/6-31G(d,p) method [43]).
This result indicates the good nonlinearity of the title molecule.
Electronic properties
UV–Vis spectral analysis
Ultraviolet spectra analysis of NPBS has been investigated in
gasphase and in ethanol solvent by theoretical calculation and is
within 200–800 nm range. The UV–Vis absorption spectrum of
the sample in ethanol is shown in Fig. 5(a) along with theoretically
predicted electronic spectra of the title molecule in ethanol and gas
phase as shown in Fig. 5(b and c) respectively. The calculated
results involving the vertical excitation energies, oscillator
strength (f) and wavelength are carried out and compared with
measured experimental wavelength shown in Table 5. The time
dependent density functional method (TD-DFT) is able to detect
accurate absorption wavelengths at a relatively small computing
time which correspond to vertical electronic transitions computed
on the ground state geometry, especially in the study of solvent
effect [44,45]; thus TD-DFT method is used with B3LYP function
and 6-31G(d,p) basis set for vertical excitation energy of electronic
spectra. Experimentally, electronic absorption spectra of title mol-
ecule in ethanol solvent showed three bands at 265, 241 and
221 nm which is good agreement with predicted electronic spectra
of the title molecule in ethanol and gas phase. The kmax is a
Table 4
The electric dipole moment, polarizability and first order hyperpolarizability of N-phenylbenzenesulfonamide by HF/6-31G(d,p) method.
Dipole moment, l (Debye) Polarizability a First order hyperpolarizability b
Parameter Value (DB) Parameter a.u. esu (Â10À24
) Parameter a.u. esu (Â10À33
)
lx 1.7129 axx 146.4573 21.7049 bxxx 92.5812 799.8089
ly À1.4703 axy 2.1378 0.3168 bxxy 42.8897 370.5241
lz 1.1583 ayy 116.9181 17.3273 bxyy 55.5939 480. 2757
l 2.6333 axz À15.3490 À2.2747 byyy À7.5406 À65.1432
ayz À18.8978 À2.8006 bxxz 1.9382 16.7441
azz 142.7615 21.1572 bxyz 25.6034 221.1877
ao 135.3789 20.0631 byyz 54.7324 472.8332
Da 38.5201 5.4236 bxzz 4.6374 40.0624
byzz À60.6373 À523.8456
bzzz 85.6643 740.0539
btot 210.3557 1817.2801
b = (1.8172 Â 1030
esu)
426 K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431

11. function of substitution, the stronger the donor character of the
substitution, the more electrons pushed into the molecule, the lar-
ger kmax. The p–pÃ
transitions are expected to occur relatively at
lower wavelength, due to the consequence of the extended aroma-
ticity of the benzene ring. The computed UV method predicts three
electronic transition at 270.58, 244.24 and 240.86 nm with an
oscillator strength f = 0.1640, 0.0017 and 0.0073 a.u. in ethanol sol-
vent and 270.81, 245.90, 242.74 nm with oscillator strength
f = 0.1224, 0.0048 and 0.0037 a.u. in gas phase respectively. These
values may be slightly shifted by solvent effects. The role of substi-
tuent of the solvent influence on the UV–spectrum. This band may
be due to electronic transition between the rings A and B (transi-
tion of p–pÃ
).
Frontier molecular orbitals
Molecular orbitals, when viewed in a qualitative graphical rep-
resentation, can provide insight into the nature of reactivity, and
some of the structural and physical properties of molecules. Both
the highest occupied molecular orbital (HOMO) and lowest unoc-
cupied molecular orbital (LUMO) are the main orbitals taking part
in chemical reactions. The HOMO energy characterizes the ability
of electron donating; LUMO characterizes the ability of electron
accepting and the gap between HOMO and LUMO characterizes
the molecular chemical stability. Energy difference between
HOMO and LUMO orbital is called as energy gap that is an
important stability for structures [46]. The energy gap is largely
responsible for the chemical and spectroscopic properties of the
200 300 400 500 600 700 800
0
1
2
3
4
5
265
221
241
Absorbance
Wavelength (nm)
240.86 nm
244.24 nm
270.58 nm
242.74 nm
245.90 nm
270.81 nm
(a)
(c)
(b)
Fig. 5. (a) The experimental UV–visible spectrum (Ethanol) of NPBS. (b) Computed UV–vis spectrum of the NPBS molecule calculated with the TD-DFT method in ethanol.
(c) Computed UV–vis spectrum of the NPBS molecule calculated with the TD-DFT method in gas phase.
K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431 427

12. molecules [47]. This also used by the frontier electron density for
predicting the most reactive position in p-electron systems and
also explains several types of reactions in conjugated systems
[48]. The conjugated molecules are characterized by a small
HOMO–LUMO separation, which is the result of a significant
degree of intramolecular charge transfer from the end-capping
electron–donor groups to the efficient electron–acceptor groups
through p-conjugated path [49]. From the plots we can see that
the region of HOMO and LUMO levels spread over the entire mol-
ecule and the calculated energy gap of HOMO–LUMO’s explains the
ultimate charge transfer interface within the molecule. In addition,
according to B3LYP/6-31G(d,p) calculation, the energy band gap of
the NPBS molecule is 5.2149 eV shown in Fig. 6. The positive and
negative phase is represented in red and green color, respectively.
HOMO energy ¼ À6:3755 eV
LUMO energy ¼ À1:1606 eV
HOMO À LUMO energy gap ¼ 5:2149 eV
The HOMO–LUMO energy gap explains the eventual charge
transfer interactions taking place within the molecule. The small
value of band gap reflects the chemical activity of the molecule
and encourages the application of NPBS as nonlinear optical
materials.
Natural population analysis
The natural atomic charges of NPBS calculated by natural pop-
ulation analysis by using the B3LYP/6–311G(d,p) method is
presented in supplementary material S1. In all these compound
among the sulfonyl S7 atom has the highest positive charge
(2.356 e) due to highly electronegative Oxygen atoms
(O8 = À0.945 e and O9 = À0.940 e) present in the adjacent position.
The ring carbon atom C11 has a positive charge (0.126 e) while
others have negative charge. It may be the reason of the substitu-
tion of Nitrogen atom N10 because of Nitrogen has the negative
charge (À0.885 e) as shown in the histogram supplementary mate-
rial S2. Natural Population Analysis shows that the H22 atom has
maximum positive atomic charges (0.435 e) than the other hydro-
gen atoms. This is due to inter molecular interaction between
nitrogen atom of NH group and Oxygen atom of the sulfonyl group
(NAHÁ Á ÁO inter molecular interaction).
Electrostatic potential, total electron density and molecular
electrostatic potential
The molecular electrostatic potential surface (MESP) which is a
method of mapping electrostatic potential onto the iso-electron
density surface simultaneously displays electrostatic potential
(electron + nuclei) distribution, molecular shape, size and dipole
moments of the molecule and it provides a visual method to
understand the relative polarity [50]. In the present study, the elec-
trostatic potential (ESP), total electron density (TED) and molecular
electrostatic potential (MEP) of NPBS are shown in Fig. 7. The color
scheme of ESP (Fig. 7a) is the negative electrostatic potentials are
shown in red (Oxygen atoms) and yellow, slightly electron rich
region (Nitrogen atom) the intensity of which is proportional to
the absolute value of the potential energy, electrostatic while green
indicates surface areas where the potentials are close to zero.
Green areas cover parts of the molecule where electrostatic poten-
tials are close to zero (CAC and CAH bonds). The total electron
Table 5
The experimental and computed absorption wavelength k (nm), excitation energies
E (eV), absorbance and oscillator strengths (f) of N-phenylbenzenesulfonamide in
Ethanol solution and gas phase.
Experimental TD-DFT/B3LYP/6-31G(d,p)
Ethanol Ethanol Gas
k (nm) Abs. k (nm) E (eV) f (a.u.) k (nm) E (eV) f (a.u.)
265 5.0582 270.58 4.5822 0.1640 270.81 4.5783 0.1224
241 4.0493 244.24 5.0764 0.0017 245.90 5.0420 0.0048
221 4.3968 240.86 5.1477 0.0073 242.74 5.1077 0.0037
LUMO Plot
)etatsdeticxetsriF(
LUMO Energy = -1.1606 eV
Energy gap = 5.2149 eV
HOMO Energy = - 6.3755 eV
(Ground state)
HUMO Plot
Fig. 6. The atomic orbital compositions of the frontier molecular orbital for N-phenylbenzenesulfonamide.
428 K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431

13. density of the title molecule computed at the 0.020000 a.u. isoden-
sity surface. The TED plots for title molecule show a uniform distri-
bution (Fig. 7b). The molecular electrostatic potential, V(r) is
related to the electronic density and is a very useful descriptor
for determining sites for electrophilic attack and nucleophilic
reactions. MEP values were calculated using the equation [51]:
VðrÞ ¼
X
ZA=jRA À rj À
Z
qðr0
Þ=jr0
À rjd
3
r0
where ZA is the charge of nucleus A located at RA, q(r0
) is the elec-
tronic density function of the molecule, and r0
is the dummy inte-
gration variable. In the present study, molecular electrostatic
potential (MEP) of NPBS are illustrated in Fig. 7c. The color code
of these maps is in the range between À5.364 eÀ2
(deepest red)
and +5.364 eÀ2
(deepest blue) in compound. The maximum positive
region is localized on the NAH bonds, indicating a possible site for
nucleophilic attack (blue color) and maximum negative region is
localized on Oxygen atoms indicating electrophilic attack (red
color). These sites give information about the region from where
the compound can have intermolecular (NAHÁ Á ÁO) interactions.
Global reactivity descriptors
By using HOMO and LUMO energy values for a molecule, the
global chemical reactivity descriptors of molecules such as hard-
ness (g), chemical potential (l), softness (S), electronegativity (v)
and electrophilicity index (x) have been defined [52,53]. On the
basis of EHOMO and ELUMO, these are calculated using the below
equations.
Using Koopman’s theorem for closed-shell molecules,
The hardness of the molecule is
g ¼ ðI À AÞ=2
(a) Electrostatic potential map
(b) Electron density map
(c) Molecular electrostatic potential map
Fig. 7. Electrostatic potential (ESP), electron density (ED) and the molecular electrostati potential map (MEP) for the N-phenylbenzenesulfonamide molecule.
K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431 429

14. The chemical potential of the molecule is
l ¼ ÀðI þ AÞ=2
The softness of the molecule is
S ¼ 1=2g
The electro negativity of the molecule is
v ¼ ðI þ AÞ=2
The electrophilicity index of the molecule is
x ¼ l2
=2g
where A is the ionization potential and I is the electron affinity of
the molecule. I and A can be expressed through HOMO and LUMO
orbital energies as I = ÀEHOMO and A = ÀELUMO. The Ionization poten-
tial A and an electron affinity I of our molecule NPBS calculated by
B3LYP/6-31G(d,p) method is 1.1606 eV and 6.3755 eV respectively.
The calculated values of the Hardness, Softness, Chemical potential,
electronegativity and electrophilicity index of our molecule is
2.6075, 0.1918, À3.7681, 3.7681 and 2.7226 respectively as shown
in supplementary material S3. Considering the chemical hardness,
large HOMO–LUMO gap represent a hard molecule and small
HOMO–LUMO gap represent a soft molecule. Energy gap of the title
molecule is large 5.2149 eV so we conclude that our molecule is
hard molecule, which is evident from Table S3 the chemical hard-
ness is 2.6075.
Thermodynamic properties
The thermodynamic functions viz, heat capacities at constant
pressure (Cp,m), entropies (Sm) and enthalpy changes (Hm) for
the title compound were evaluated from the theoretical harmonic
frequencies obtained from B3LYP/6-31G(d,p) method in the tem-
perature range 100–1000 K and listed in supplementary material
S4, it can be observed that these thermodynamic parameters
increase with rise of temperature due to the fact that the molecular
vibrational intensities increase with temperature [54]. The correla-
tion equations between heat capacity, entropy, enthalpy changes
and temperatures are fitted by quadratic formulas. Fitting factor
(R2
) of the thermodynamic functions such as heat capacity, entropy
and enthalpy changes are 0.954, 0.994 and 0.975 respectively. The
correlation graphics of temperature dependence of thermody-
namic functions for NPBS molecule are shown in supplementary
material S5. Vibrational zero-point energy of the NPBS is Vibra-
tional zero-point energy is 526.45 kJ/mol.
FTNMR analysis
The characterization of compound NPBS was further enhanced
by the use of 1
H and 13
C NMR spectroscopy. Theoretical 1
H and
13
C NMR chemical shift values of the title compound have been
computed using the same method and the basis set for the opti-
mized geometry and the results were compared with closely
related molecule N-(2-aminophenyl) benzene sulfonamide [55].
The NMR spectra of the compounds were recorded on a Bruker
300 MHz Ultrashield TM NMR spectrometer, and are shown in
the supplementary material S6 and the chemical shifts are tabu-
lated in Table 6. In the 13
C NMR spectrum, the signal at
138.8 ppm is assigned to the C11 carbon of the phenyl ring B which
is bonded with NAH group, calculated as 127.5 ppm. The signal at
143.6 ppm is assigned to the C1 carbon of the phenyl ring A, which
is bonded with sulfonyl group, calculated as 134.1 ppm. The Meta
carbons (C3, C5) of the phenyl ring A are responsible for the signal
at 127.6 ppm, calculated as 117.8 and 118.4 ppm for C3 and C5
respectively. The ortho carbons (C2, C6) of the phenyl ring A are
responsible for the signal at 129.0 ppm, calculated as 116.6 ppm
and 116.0 ppm for C2 and C6 respectively. The signals at
121.4 ppm, 117.6 ppm, 119.2 ppm, 129.1 ppm are assigned to the
(C13, C14, C15 and C16) carbons of the ring B. The above said car-
bons of the phenyl ring B are calculated as, 118.3 ppm, 114.5 ppm,
118.9 ppm and 111.8 ppm by B3LYP method. In the 1
H NMR spec-
tra of compound,the H24, H25, H27 and H26 protons belonging to
phenyl ring B were appeared as doublet, triplet, doublet and triplet
in 1:1:1:1 ratio at 6.48 ppm, 6.56 ppm, 6.80 ppm and 7.06 ppm,
respectively, this is good agreement with computed chemical shifts
at 6.96 ppm, 6.98 ppm, 7.79 ppm and 7.26 respectively. Similarly,
the H18–20, H19 and H17–21 protons belonging to phenyl ring A
backbone were observed as triplet, doublet and doublet in 2:1:1
ratio at 7.48 ppm, 7.59 ppm, 7.77 ppm, respectively. These chemi-
cal shifts also coincide very well with theoretically computed val-
ues at 7.11 ppm, 7.42 ppm, 7.38 ppm, 7.19 ppm and 7.77 ppm for
H18, H20, H19, H17 and H21 respectively. However, the spectra
do not contain a signal corresponding to amide NH proton which
is observed at 5.22 ppm theoretically. As it is seen from the Table
6, calculated 1
H and 13
C chemical shifts values of the title com-
pound are generally agreement with the experimental 1
H and 13
C
chemical shifts data.
Conclusion
The synthesis and the electronic and infrared and Raman spec-
troscopic studies of the molecule N-phenylbenzenesulfonamide
were performed. The results are complemented and discussed
within the scope of quantum chemical calculations with DFT calcu-
lations. The difference between the observed and scaled wavenum-
ber values of most of the fundamentals is very small. The MEP map
shows that the negative potential sites are on oxygen atoms as well
as the positive potential sites are around the hydrogen atoms.
These sites may provide information about the possible reaction
regions for the title structure. The value of the energy separation
between the HOMO and LUMO is very large 5.983 eV and this
energy gap gives significant information about the title compound.
So we conclude that our molecule NPBS is hard molecule, which is
evident from the value of chemical hardness is 2.992 which is
greater than that of value of chemical softness is 0.167. The UV
spectrum was measured in ethanol solution and results are com-
pared with theoretical results. The calculated first order hyperpo-
larizability was found to be 1.8172 Â 10À30
esu, much greater
than reported in literature for urea. This study also demonstrates
that the title compound can be used as a good nonlinear optical
material. This ab initio calculated nonzero b values show that our
title molecule can be good candidates for nonlinear optical activity.
Table 6
The observed and predicted 1
H and 13
C NMR isotropic chemical shifts (with respect to
TMS, all values in ppm) for N-phenylbenzenesulfonamide.
Atom
position
Experimentala
B3LYP/6-
31G(d,p)
Atom
position
Experimentala
B3LYP/6-
31G(d,p)
C1 143.6 134.1 H17 7.77 7.19
C2 129.0 116.6 H18 7.48 7.11
C3 127.6 117.8 H19 7.59 7.38
C4 128.6 122.6 H20 7.48 7.42
C5 127.6 118.4 H21 7.77 7.75
C6 129.0 116.0 H22 – 5.22
C11 138.8 127.5 H23 – 6.20
C12 – 110.5 H24 6.48 6.96
C13 121.4 118.3 H25 6.56 6.98
C14 117.6 114.5 H26 7.06 7.26
C15 119.2 118.9 H27 6.80 7.79
C16 129.1 111.8 – –
a
Taken from Ref. [55].
430 K. Govindarasu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 417–431

15. Natural Population Analysis shows that the H22 atom has maxi-
mum positive atomic charges (0.435 e) than the other hydrogen
atoms. This is due to inter molecular interaction between nitrogen
atom of NH group and Oxygen atom of the solfonyl group
(NAHÁ Á ÁO inter molecular interaction). Thermodynamic properties
in the range from 100 to 1000 K are obtained. The gradients of C0
p
and S0
m to the temperature decreases, but that of DH0
m increases,
as the temperature increases. Theoretical 1
H and 13
C chemical shift
values were reported and compared with experimental data,
showing good agreement for both 1
H and 13
C.
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.2014.06.040.
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