1. Molecular structure, vibrational spectra, NBO, UV and first order
hyperpolarizability, analysis of 4-Chloro-DL-phenylalanine by density
functional theory
K. Govindarasu, E. Kavitha ⇑
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
4CLPA 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 4-Chloro-DL-phenylalanine.
a r t i c l e i n f o
Article history:
Received 2 April 2014
Received in revised form 29 May 2014
Accepted 3 June 2014
Available online 13 June 2014
Keywords:
4-Chloro-DL-phenylalanine
TD-DFT
NBO
UV–Vis
MEP
Hyperpolarizability
a b s t r a c t
The Fourier transform infrared (4000–400 cmÀ1
) and Fourier transform Raman (3500–50 cmÀ1
) spectra of
4-Chloro-DL-phenylalanine (4CLPA) were recorded and analyzed. The equilibrium geometry, bonding
features and harmonic vibrational wavenumbers were investigated with the help of density functional
theory (DFT) method using B3LYP/6-31G(d,p) as basis set. The observed vibrational wavenumbers were
compared with the calculated results. Natural bond orbital analysis confirms the presence of intramolec-
ular charge transfer and the hydrogen bonding interaction. Predicted electronic absorption spectra from
TD-DFT calculation have been analyzed comparing with the UV–Vis (200–800 nm) spectrum. The effects
of chlorine and ethylene group substituent in benzene ring in the vibrational wavenumbers have been
analyzed. The HOMO–LUMO energy gap explains the charge interaction taking place within the molecule.
The first order hyperpolarizability (b0) and related properties (b, a0 and Da) of 4CLPA were calculated. The
Chemical reactivity and chemical potential of 4CLPA is calculated. In addition, molecular electrostatic
potential (MEP), frontier molecular orbital (FMO) analysis were investigated using theoretical
calculations.
Published by Elsevier B.V.
Introduction
Nonlinear optical (NLO) materials have attracted the attention
of researchers owing to their great potential applications in various
fields due to their properties such as the large NLO coefficient,
http://dx.doi.org/10.1016/j.saa.2014.06.019
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) 799–810
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa

2. ultrafast nonlinear response time, and high optical damage thresh-
old [1,2]. The recent interest in new organic materials for photonics
aims at finding criteria for the preparation of the best materials with
large nonlinear optical (NLO) response. Amino acids are the control
units of proteins and play important roles in determining their struc-
tures and functions. Further, only 20 naturally existing amino acids
form almost all proteins in the cellular processes [3]. In the organic
class, amino acids exhibit some specific features such as molecular
chirality, weak vander Waals interaction, hydrogen bonds and zwit-
terionic nature of the molecule which favors crystal hardness [4].
Phenylalanine is one of the twenty biologically naturally occurring
amino acids that can be found in protein. 4-Chloro-DL-phenylalanine
is the one of the phenylalanine derivative in contains three different
functional groups, that is, an amino group (ANH2), a carboxyl group
(ACOOH) and chlorophenyl group (C6H5CH2ClA), are connected
through the Ca–Cb bridge. There have been several spectroscopic
studies on the behavior of many amino acids and peptides including
phenylalanine and on complexes involving amino acids, organic
molecules and metal ions [5,6].
Vijaya Chamundeeswari et al. [7] reported Molecular structure
and spectroscopic studies of 3,4-dihydroxy-L-phenylalanine using
density functional theory. Amalanathan et al. [8] investigated
Density functional theory studies on molecular structure and
vibrational spectra of NLO crystal L-phenylalanine phenylalanium
nitrate. Podstawka et al. [9] assigned Surface-enhanced Raman,
FT-Raman, and infrared studies of L-phenylalanine. To best of our
knowledge, there is not any review summarizing the literature
on the DFT frequency calculations of 4CLPA have been reported
so far. Quantum chemical calculations are excellent methods in
the design of NLO molecules and help to predict some properties
of the new materials, such as molecular dipole moments, polariz-
abilities and hyperpolarizabilities [10,11].
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 4CLPA. Vibrational spectra of
4CLPA have been analyzed on the basis of calculated total energy
distribution (TED). Theoretically computed vibrational wavenum-
bers were compared with experimental values. The natural bond
orbital (NBO) analysis can be employed to identify and substanti-
ate the possible intra and intermolecular interactions between
the units that would form the H-bonded network. The UV–Vis
spectroscopic studies along with HOMO–LUMO analysis have been
used to explain the charge transfer within the molecule.
FT-IR, FT-Raman and UV–Vis spectral measurements
The compound 4-Chloro-DL-phenylalanine in the solid form was
purchased from TCI INDIA chemical company at Chennai, with a
stated purity greater than 98% and it was used as such without fur-
ther purification. The FT-IR spectrum of this compound was
recorded in the range of 4000–400 cmÀ1
on a BRUKER Optik GmbH
FT-IR spectrometer using KBr pellet technique. The spectrum 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 4CLPA 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 molar solu-
tion of 4CLPA, dissolved in ethanol. 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 Electrochemical Research Institute (CECRI), Karaiku-
di 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 4CLPA in the
present work. The entire calculations were performed using Gauss-
ian 03W program package [12]. Furthermore, theoretical vibra-
tional spectra of the title compound were interpreted by means
of TED using the VEDA 4 program [13]. The Natural Bond Orbital
(NBO) calculations were performed using NBO 3.1 program [14]
as implemented in the Gaussian 03W [12] 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 4CPLA are calculated using HF/6-31G(d,p) basis set,
based on the finite-field approach [15]. 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
[12] has been converted to relative Raman intensities (IR
). The
492
615
707
861
922
1068
1184
1245
1330
1384
1476
1606
1799
2936
2990
3059
3305
3444
3737
3263
3024
2756
2673
2482
2248
1990
1851
1745
1548
1448
1371
1240
1182
1126
1059
899
831
740
629
565
474
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm-1
)
B3lyp/6-31G (d,p)
Experimental
Transmittance(%)IRintensity(arb.units)
Fig. 1. Comparison of experimental and theoretical B3LYP/6-31G(d,p) FT-IR spectra
for 4-Chloro-DL-phenylalanine.
800 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810

3. theoretical Raman intensity (IR
), which simulates the measured
Raman spectrum, is given by the equation [16,17]:
IR
i ¼ Cðm0 À miÞ4
vÀ1
i BÀ1
i Si ð1Þ
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 intensi-
ties have been computed assuming Bi equal 1. The theoretical
Raman spectra have been calculated by the Raint program [18].
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 [19]. In order to describe confor-
mational flexibility of the title molecule, the energy profile as a
function of C5AC4AC3AN2 and C6AC5AC4AC3 torsion angles
were achieved with B3LYP/6-31G(d,p) method. Possible conformers
of 4CLPA depend on the rotation of C3AC4 bond, linked to phenyl
and alanine group. During the calculation all the geometrical
parameters were simultaneously relaxed while the C5AC4AC3AN2
and C6AC5AC4AC3 torsional angles were varied steps of 10° up to
360°. The conformational energy profile shows two maxima near
60° (À1012.72 Hartree) and 170° (À1012.84 Hartree) for
T (C5AC4AC3AN2) torsion angle and 40° (À1014.38 Hartree) and
220° (À1014.38 Hartree) for T (C6AC5AC4AC3) respectively. It is
clear from supplementary material S1, there are two local minima
(stable conformers) observed at 0° or 360° (À1014.40 Hartree)
and 110° (À1014.41 Hartree) for T (C5AC4AC3AN2). Similarly
T (C6AC5AC4AC3) has two local minima at 0° or 360°
(À1014.25 Hatree) and 110° (À1014.14 Hartree). Further results
are based on the most stable conformer of 4CLPA molecule to clarify
molecular structure 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.
The atom numbering scheme adopted in this study is given in
Fig. 3. To the best of our knowledge, experimental data on the geo-
metric structure of the title molecule are not available till date in
the literature. Our molecule 4CLPA is compared with XRD data of
closely related molecules N,N0
-[(8-endo, 11-endo-Dihydroxypenta-
cyclo undecane 8, 11 diyl) bis (methylene carbonyl)] di-L-phenylal-
anine [20] and 1-Benzyloxy-4-chlorobenzene [21]. In this study
only L-phenylalanine part of the molecule [20] is taken for compar-
ison. In the benzene ring, CAC bond length is about 1.396 Å [22].
The calculated CAC bond length in phenyl ring varies from 1.392
to 1.403 Å by DFT method which is good agreement with experi-
mental data (1.382–1.390 Å). In our case the CAC bonds in phenyl
ring are not of the same bond length. Many authors [23–25] have
been explained the changes in frequency or bond length of the
CAH bond on substitution due to change in the charge distribution
on the carbon atom of the benzene ring. The carbon atoms are
bonded to hydrogen atoms with h bond in benzene ring. Substitu-
tion of Cl (electron withdrawing nature) for hydrogen atom
reduces the electron density at the ring carbon atom. The ring car-
bon atom in the substituted benzene exert large attraction on the
valance electron cloud of hydrogen atom resulting increase in the
CAH force constant and a decrease in the corresponding bond
length. The reverse holds well on substitution with electron donat-
ing groups [26]. The chlorine (electronegative) atom (Cl13) is
bonded to carbon atom (C8) of the phenyl ring. Due to this electro-
negative substitution the phenyl ring appears a little distorted, the
bond length C7AC8 = 1.395 Å and C8AC9 = 1.392 Å which is
shorter than C9AC10 = 1.397 Å and C6AC7 = 1.393 Å by DFT
method at the rest of the substitution. On the other hand, with
ethyl group (electron donating nature) substitution on the phenyl
ring, the bond length C5AC6 = 1.403 Å and C5AC10 = 1.401 Å
which is longer than C9AC10 = 1.397 Å and C6AC7 = 1.393 Å by
DFT method at the rest of the substitution. The highest value of
bond length C3AC4 = 1.548 Å calculated by DFT method, due to
repulsion between CHACH2 group of alanine. All the CAH bond
lengths are presented as nearly equal values at C6AH19 =
1.087 Å, C7AH20 = 1.084 Å, C9AH21 = 1.084 Å and C10AH22 =
1.087 Å by DFT method, which is good agreement with experimen-
tal findings at 0.950 Å. On the other hand, a small increment occurs
in the ethyl group C4AH17 = 1.094 Å and C4AH18 = 1.096 Å bonds.
The NAH bond distances are exactly equal N2AH14 = 1.017 Å and
N2AH15 = 1.017 Å by DFT method. The carboxyl group bond dis-
tances are C1@O11@1.209 Å and C1AO12 = 1.340 Å which are very
close to experimental value 1.202 Å and 1.333 Å respectively. The
calculated CACl bond length is found at C1ACl3 = 1.758 Å, this
value 0.012 Å differed from the experimental value 1.746 Å. From
the theoretical values, it is found that most of the optimized bond
3912
3754
3651
3480
33743349
3192
3067
2926
2865
2695
2633
2564
2421
2197
2109
1896
1825
1675
1599
1445
1345
1214
1158
1092
1042
994951
845805
716676633
521
435
354
296
238
116
6838
169
307
361
623
707
792
861
945
1061
1184
1238
1330
1445
1583
1799
2921
2990
3098
3367
4000 3500 3000 2500 2000 1500 1000 500
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 4-Chloro-DL-phenylalanine.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810 801

4. lengths are slightly larger than the experimental 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 appears to be a little distorted because of the
Cl group substitution as seen from the bond angles C7AC8AC9,
which are calculated as (120.9°) by DFT method and larger than
typical hexagonal angle of (120°). With the electron donating
(ethyl) substituent on the benzene ring, the symmetry of the ring
is distorted, yielding ring angles smaller than (120°) at the point
of substitution [27]. It is observed from that the bond angle at
the point of the substitution C6AC5AC10 (118.1°) by DFT method
and (118.2°) by experimental value. The dihedral angel between
the ethyl group and phenyl ring is C4AC5AC6AC7 (178.68°) and
C4AC5AC10AC9 (À178.60°) and Chlorine atom and phenyl ring
is C6AC7AC8ACl13 (À179.96°) and alanine group and phenyl ring
is C1AC3AC4AC (175.21°).
Vibrational assignments
The vibrational spectral analysis is performed on the basis of
characteristic vibrations of carboxylic acid, methylene and phenyl
ring vibrations. The observed and calculated frequencies using
B3LYP/6-31G(d,p) basis set and along with their relative intensi-
ties, probable assignments and the total energy distribution
(TED) of the title molecule are summarized in Table 2. A
complete assignment of the fundamentals was proposed based
on the calculated TED values, infrared and Raman intensities. The
title molecule consists of 23 atoms, which undergo 63 normal
modes of vibrations. It agrees with C1 point group symmetry, all
Table 1
Calculated optimized parameter values of the 4-Chloro-DL-phenylalanine [bond length in (Å), angles in (°)].
Bond length B3LYP Expa,b
Bond angle B3LYP Expa,b
Dihedral angle B3LYP Expa,b
C1AC3 1.543 1.526 C3AC1AO11 122.5 125.2 O11AC1AC3AN2 167.52
C1AO11 1.209 1.202 C3AC1AO12 113.7 109.6 O11AC1AC3AC4 À71.22
C1AO12 1.340 1.333 O11AC1AO12 123.8 125.0 O11AC1AC3AH16 45.01
N2AC3 1.472 1.447 C3AN2AH14 111.0 107.4 O12AC1AC3AN2 À14.56
N2AH14 1.017 0.950 C3AN2AH15 110.8 O12AC1AC3AC4 106.70
N2AH15 1.017 H14AN2AH15 106.8 O12AC1AC3AH16 À137.08
C3AC4 1.548 1.539 C1AC3AN2 109.3 111.2 C3AC2AO12AH23 2.46
C3AH16 1.097 1.000 C1AC3AC4 108.1 112.9 O11AC1AO12AH23 À179.65
C4AC5 1.513 1.514 C1AC3AH16 106.7 107.4 H14AN2AC3AC1 150.79
C4AH17 1.094 0.990 N2AC3AC4 111.3 110.0 H14AN2AC3AC4 31.50
C4AH18 1.096 0.990 N2AC3AH16 113.1 107.4 H14AN2AC3AH16 À90.61
C5AC6 1.403 1.390 C4AC3AH16 108.3 107.4 H15AN2AC3AC1 À90.69
C5AC10 1.401 1.384 C3AC4AC5 113.3 110.1 H15AN2AC3AC4 150.01
C6AC7 1.393 1.388 C3AC4AH17 106.8 109.6 H15AN2AC3AH16 27.91
C6AH19 1.087 0.950 C3AC4AH18 108.5 109.6 C1AC3AC4AC5 175.21 170.36
C7AC8 1.395 1.374(b)
C5AC4AH17 110.8 109.6 C1AC3AC4AH17 52.91
C7AH20 1.084 0.950 C5AC4AH18 110.0 109.6 C1AC3AC4AH18 À62.30
C8AC9 1.392 1.382(b)
H17AC4AH18 107.1 108.1 N2AC3AC4AC5 À64.81
C8ACl13 1.758 1.746(b)
C4AC5AC6 120.7 120.9 N2AC3AC4AH17 172.89
C9AC10 1.397 1.391 C4AC5AC10 121.2 120.7 N2AC3AC4AH18 57.69
C9AH21 1.084 0.950 C6AC5AC10 118.1 118.2 H16AC3AC4AC5 60.03
C10AH22 1.087 0.950 C5AC6AC7 121.3 120.8 H16AC3AC4AH17 À62.27
O12AH23 0.988 C5AC6AH19 119.6 119.6 H16AC3AC4AH18 À177.48
C7AC6AH19 119.1 119.6 C3AC4AC5AC6 À75.03
C6AC7AC8 119.2 120.1 C3AC4AC5AC10 103.87
C6AC7AH20 120.8 119.9 H17AC4AC5AC6 45.06
C8AC7AH20 120.0 119.9 H17AC4AC5AC10 À136.05
C7AC8AC9 120.9 120.9(b)
H18AC4AC5AC6 163.35
C7AC8ACl13 119.5 119.3(b)
H18AC4AC5AC10 À17.75
C9AC8ACl13 119.6 119.6(b)
C4AC5AC6AC7 178.68 178.7(b)
C8AC9AC10 119.0 119.9 C4AC5AC6AH19 À1.82
C8AC9AH21 120.2 120.1 C10AC5AC6AC7 À0.25
C10AC9AH21 120.8 120.1 C10AC5AC6AH19 179.26
C5AC10AC9 121.4 121.1 C4AC5AC10AC9 À178.60 À177.8(b)
C5AC10AH22 119.6 119.5 C4AC5AC10AH22 2.43
C9AC10AH22 119.0 119.5 C6AC5AC10AC9 0.33
C1AO12AH23 104.5 C6-C5AC10AH22 À178.64
C5AC6AC7AC8 À0.06
C5AC6AC7AH20 179.63
H19AC6AC7AC8 A179.57
H19AC6AC7AH20 0.12
C6AC7AC8AC9 0.30
C6AC7AC8ACl13 A179.96 À177.57(b)
H20AC7AC8AC9 À179.39
H20AC7AC8ACl13 0.35
C7AC8AC9AC10 À0.22 À0.3
C7AC8AC9AH21 179.40
Cl13AC8AC9AC10 À179.96
Cl13AC8AC9AH21 À0.34
C8AC9AC10AC5 À0.10
C8AC9AC10AH22 178.88
H21AC9AC10AC5 À179.72
H21AC9AC10AH22 À0.75
a,b
Taken from Refs. [20,21].
802 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810

5. vibrations are active both in Raman and infrared absorption. The
small difference between the experimental and calculated vibra-
tional modes could be attributed to the fact that the experimental
results belong to solid phase while the theoretical belong to
isolated gaseous phase. 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
[28], the deviation from the experiments is less than 10 cmÀ1
with
few exceptions. Comparison of the frequencies calculated at
(B3LYP) method using 6-31G(d,p) basis set with experimental val-
ues reveals that the 6-31G(d,p) basis set result shows very good
agreement with experimental observations, even for a complex
molecular system. The vibrational assignments for different
functional groups have been discussed below.
Phenyl ring vibrations
For benzene derivatives, the CH stretching modes are expected
in the region 3105–3000 cmÀ1
[29]. There are four aromatic CH
stretching modes (mode no: 4, 5, 6, 7) for our title molecule. In
the present study CH stretching vibration of the phenyl ring
observed at 3062 cmÀ1
in FT-IR spectrum and 3067 cmÀ1
in FT-
Raman spectrum. The theoretically predicted wavenumbers at
3094, 3093, 3058 and 3054 cmÀ1
by DFT method are assigned CH
stretching vibrations of phenyl ring. The CACAH in-plane bending
vibrations are normally occurred as a number of strong to weak
intensity bands in the region 1300–1000 cmÀ1
[30]. In disubsti-
tuted benzenes, there should be four CH in-plane bending vibra-
tions (mode no: 17, 21, 27 and 29). The CACAH in-plane bending
vibrations observed at 1153 and 1093 in FT-IR spectrum and
1092 cmÀ1
in FT-Raman spectrum. The calculated wavenumbers
at 1391, 1298, 1161 and 1086 cmÀ1
by DFT method assigned
CACAH inplane bending vibrations. The CAH out-of-plane bending
vibrations are strongly coupled vibrations and occur in the region
1000–750 cmÀ1
[31]. In the present study CAH out-of-plane bend-
ing vibrations observed at 858 cmÀ1
in FT-IR spectrum 950 and
820 cmÀ1
in FT-Raman spectrum. The computed wavenumbers at
948, 933, 859 and 833 cmÀ1
are assigned CAH out-of-plane bend-
ing vibrations. The carbon–carbon stretching modes of the phenyl
group are expected in the range from 1650 to 1200 cmÀ1
[32].
There is six equivalent CAC bonds in benzene and consequently
there will be six CAC stretching vibrations. The bands are observed
at 1591 and 1548 cmÀ1
in FT-IR spectrum and 1476 cmÀ1
in FT-
Raman spectrum are identified as CAC stretching vibrations. The
computed wavenumbers at 1586, 1561, 1474, 1391, 1298 and
1227 cmÀ1
by DFT method assigned CAC stretching vibrations
which indicate a good agreement with our experimental findings.
The in-plane deformation vibration is at higher frequencies than
the out-of plane vibrations. Shimanouchi et al. [33] gave the fre-
quency data for these vibrations for different benzene derivatives
as a result of normal coordinate analysis. In our case the bands
observed at 1182 cmÀ1
in FT-IR spectrum 994 and 743 cmÀ1
in
FT-Raman spectrum are identified CACAC in plane bending
vibrations of the phenyl ring which is coincidence with calculated
wavenumbers at 1586, 1180, 990 and 794 cmÀ1
by DFT method.
The CACACAC torsion bending vibrations observed at 740 and
474 cmÀ1
in FT-IR spectrum 716, 633 and 464 cmÀ1
in FT-Raman
spectrum. The computed wavenumbers at 708, 631, 497, 408 cmÀ1
by DFT method assigned CACACAC torsion bending vibrations.
Sudha et al. [34] assigned the ring breathing mode for the para
substituted benzene is at 715 cmÀ1
in FT-IR and at 736 cmÀ1
in the-
oretically. In our present study the computed wavenumber at
797 cmÀ1
identified as ring breathing mode (mode no:41).
Methylene vibrations
For the assignments of CH2 group frequencies, basically six fun-
damentals can be associated with each CH2 group namely CH2
symmetric stretch; CH2 asymmetric stretch; CH2 scissoring and
CH2 rocking, which belongs to in-plane vibrations and two out-of
plane vibrations, viz., CH2 wagging and CH2 twisting modes, which
are expected to be depolarized. The asymmetric CH2 stretching
vibrations are generally observed in the region 3100–3000 cmÀ1
,
while the symmetric stretch will appear between 3000 and
2900 cmÀ1
[35]. The CH2 asymmetric stretching vibration observed
at 3003 cmÀ1
in FT-Raman spectrum and computed at 2992 cmÀ1
by DFT method. The band at 2946 cmÀ1
observed CH symmetric
stretching vibration of the CH2 group and computed at
2938 cmÀ1
by DFT method this is good agreement with experimen-
tal findings. The CH2 scissoring vibrations appear normally in the
region 1490–1435 cmÀ1
as medium intense bands [36]. In our
present study this band was observed at 1448 cmÀ1
in FT-IR
spectrum and 1445 cmÀ1
in FT-Raman spectrum. The theoretically
predicted wavenumber at 1442 cmÀ1
assigned CH2 scissoring
vibration (mode no. 16) which evident from the TED colomn
almost contributes to 73%. Absorption of hydrocarbons due
to CH2 twisting and wagging vibration is observed in the
1350–1150 cmÀ1
region [37]. These bands are generally apprecia-
bly weaker than those resulting from CH2 scissoring vibration.
The CH2 wagging and twisting modes are assigned at 1309 and
1186 cmÀ1
respectively by DFT method.
Amino group vibrations
The NH2 group gives rise to six internal modes of vibrations viz.,
the symmetric stretching, the anti symmetric stretching, the sym-
metric deformation or the scissoring, the rocking, the wagging and
torsional modes. The NH2 group has two NH stretching vibrations,
one being asymmetric and the other symmetric. The frequency of
asymmetric vibration is higher than that of symmetric one. The
asymmetric NH2 stretching mode appears from 3500 to
3420 cmÀ1
and symmetric NH2 stretching is observed in the range
3420–3340 cmÀ1
[38]. In our case the asymmetric and symmetric
stretching vibrations calculated at 3447 and 3370 cmÀ1
, TED calcu-
lations shows 99% and 97% contribution of NH2 asymmetric and
symmetric stretching vibrations in modes1 and 2, respectively.
Bellamy [39] has suggested that the NH2 scissoring mode lies in
the region 1529–1650 cmÀ1
. The NH2 scissoring type in plane
bending vibration observed at 1599 cmÀ1
in FT-Raman spectrum
and this vibration also predicted at 1605 cmÀ1
by DFT method.
The observed FT-Raman spectra (1599 cmÀ1
) is slightly (6 cmÀ1
)
deviate from the theoretically predicted wavenumber
(1605 cmÀ1
). The shift in experimental value is probably associated
to intramolecular hydrogen bonding O12AH23Á Á ÁN2 which is sup-
ported by atomic charge calculation a large negative charge on the
N2 (À0.946 e) and positive charge on H23 (0.51493 e) supports the
Fig. 3. Optimized molecular structure and atomic numbering of 4-Chloro-DL-
phenylalanine.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810 803

6. existence of this bonding (see section ‘‘Natural population analy-
sis’’). NBO analysis (see section ‘‘NBO analysis’’) also supports the
formation of an intra molecular O12AH23Á Á ÁN2 hydrogen bonding.
For L-asparagine and L-glutamine the wagging mode NH2 is
reported at 804, 780 cmÀ1
and 783, 777 cmÀ1
respectively [40].
The frequency in the FT-Raman spectrum at 894 cmÀ1
assigned
Table 2
Comparison of the experimental and calculated vibrational spectra and proposed assignments of 4-Chloro-DL-phenylalanine.
Mode nos. Experimental wavenumbers (cmÀ1
) Theoretical wavenumbers/cmÀ1
TED (P10%) with vibrational assignments
B3LYP/6-31G(d,p)
FT-IR FT-Raman Unscaled Scaled IIR
a
IRA
b
1 3588 3447 18.48 2.22 tNH(99) NH2 asym.str
2 3508 3370 9.64 4.79 tNH(97) NH2 sym.str
3 3437 3302 71.93 3.05 tOH(97) OAH sym.str. in COOH
4 3220 3094 3.45 8.90 tCH(93) CH str.in benzene ring
5 3219 3093 8.5 2.11 tCH(94) CH str.in benzene ring
6 3062 3067 3183 3058 11.86 3.23 tCH(90) CH str.in benzene ring
7 3179 3054 13.6 3.38 tCH(90) CH str.in benzene ring
8 3003 3114 2992 10.63 2.88 tCH(92) CH assym.str.in CH2
9 2946 3058 2938 21.02 2.67 tCH(83) CH sym.str.in CH2
10 2926 3043 2924 13.7 4.72 tCH(87) CH sym.str.in C3H16
11 1745 1825 1873 1800 79.81 1.75 tOC(77) C@O str. in COOH
12 1599 1670 1605 23.36 2.79 dHNHsci(84) in NH2
13 1591 1651 1586 12.67 16.22 tCC(56) in ring
14 1548 1625 1561 3.24 1.24 tCC(73) in ring + dHCC(12) in ring
15 1476 1534 1474 34.4 0.20 tCC(11) in ring + dCCC(12) in ring
16 1448 1445 1501 1442 11.51 2.72 dHCHsci(79) in CH2 + dHCCO(11)
17 1448 1391 25.14 0.16 tCC(41) in ring + dHCC(33) in ring
18 1371 1380 1444 1387 100 1.83 dH23O12C1(85) in COOH + tC1AO12 in COOH
19 1321 1345 1382 1328 17.18 8.37 sH16C3C1O12(57)
20 1362 1309 10.32 3.62 sH16C3C1O12(29) + dH16C3C4(43)+CH2 wagging
21 1351 1298 11.32 0.68 tCC(31) in ring + dHCC(13) in ring + dHCCO(10)
22 1329 1277 1.54 0.23 tCC(18) in ring + dHCC(67) in ring
23 1240 1248 1298 1247 7.59 2.69 sH23C1C3O12(18) + dH16N2C3(32) + dH18C4C5(11
24 1214 1285 1235 7.96 5.39 dH16C3C4(59)
25 1234 1186 21.34 4.44 sCH2 twist + tC1C3(20)
26 1182 1228 1180 4.02 7.30 dCCC(11) in ring + dH17C4C5(14)
27 1153 1208 1161 2.97 1.99 dHCC(76) ring
28 1126 1168 1122 12.12 2.06 sH16C3C1O11(15) + dH16C3C4(21) + dH16N2C3(16)
29 1093 1092 1130 1086 13.77 0.43 tC3C4(42) + dHCC(29) ring
30 1110 1066 35.58 11.66 dC7C8C9(16)
31 1059 1056 1105 1062 13.94 7.01 tN2C3(40) + dH16C3C1(10)
32 994 1030 990 22.64 0.62 dCCC(68) in ring
33 950 987 948 36.12 6.63 cCCCH(16) in ring + dH14N2C3(16) + sH18C4C3N2(11)
34 971 933 6.18 0.11 sH19C6C7H20(12) + cCCCH(77) in ring
35 965 927 15.88 1.53 sH21C9C10H22(71) in ring+
36 960 922 26.22 1.88 cN2H15C3H16(33) + sH21C9C10H22(10) in ring
37 894 897 862 35.48 3.54 sH23O12C1C3(15) + cO11C1O12C3(10) + NH2 wag
38 858 894 859 23.47 1.65 cCCCH(10) in ring + sH23O12C1C3(47)
39 820 867 833 34.09 2.22 cCCCH(20) in ring + sH14N2C3C4 (17)
40 804 805 844 811 2.28 3.45 sHCCC(97)
41 829 797 21.42 0.98 sHCCC(62) + ring breathing
42 743 826 794 19.18 5.63 dCCC(29) in ring + tC4C5
43 740 716 737 708 17.5 11.20 sCCCC(51) in ring + dC1C3N2(18) + sC5C4C3N2(15) + sNCC@O
44 675 676 727 699 4.72 0.42 dC1C3N2(18)
45 633 657 631 8.57 1.80 sCCCC(15) in ring + dC1C3C4(23) + cO11C1O12C3(28)
46 648 623 4.86 5.38 dCCC(72) ring
47 602 643 618 13.06 0.84 dC3C1O11(19) + dC3C1O12(10) + tCCl(17)
48 519 521 554 532 10.51 2.30 dC1C3N2(13) + dO11@C1O12 (37)
49 474 464 514 494 15.81 2.24 sCCCC(11) in ring + sH19C6C5C4(10) + cC1C3N2C4(12)
50 425 408 4.53 0.98 sCCCC(69) in ring
51 402 420 404 6.5 0.80 dC4C3N2(10)
52 399 383 8.82 4.86 dC4C3N2(16) + dC1C3C4(10)
53 354 374 359 11.56 5.98 dC7C8Cl13(17) + dC3C4C5(16) + cC3C4N2C5(26)
54 323 346 332 15.2 1.89 dC1C3N2(65)
55 319 306 7.05 6.98 dC4C3N2(17) + sC1C3C4C5(15) + sH15N2C3C4(10)
56 296 302 290 25.57 3.31 dC1C3C4(13) + dC8C9Cl(22) + NH2 twist
57 238 253 243 5.77 1.61 sH14N2C3C4(26) + dC7C8Cl13(33) + dC4C3N2(10)
58 174 167 7.58 7.35 sC4C3C1O11(33) + dC1C3C4(16)+sH23O12C1C3(12)
59 116 154 148 9.94 1.09 sC5C4C3N2(15) + cCl13C5C4C3(22) + dC1C3C4(30) + dC4C3N2(10)
60 68 79 76 3.79 21.36 cC1C3C4C5(37) + cC1C3N2C4(47)
61 54 52 6.88 26.98 cC1C3N2C4(18) + sC4C3C1O12(54)
62 47 45 10.98 19.06 sC1C3C4C5(60)
63 41 39 4.51 100.00 Lattice vibrations
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%).
804 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810

7. to NH2 wagging mode which is computed at 862 cmÀ1
by the DFT
method. The NH2 twisting vibration observed at 296 in FT-Raman
spectrum. The calculated wavenumber at 290 cmÀ1
assigned NH2
twisting vibration which is good correlate with experimental
value. Also NH2 out of plane bending calculated at 922 cmÀ1
by
DFT method, TED contributes this mode is 33%.
Carboxylic group vibrations
In solid phase, the C@O group of saturated aliphatic carboxylic
acid absorbs strongly in the region 1740–1715 cmÀ1
[41]. In our
case the observed band at 1745 cmÀ1
in FT-IR spectrum and
1825 cmÀ1
in FT-Raman spectrum and theoretically predicted
wavenumber at 1800 cmÀ1
identified as C@O stretching vibration.
The deviation between the theoretical and experimental value is
may be due to inter molecular interaction between two carboxylic
groups. The C@O stretching vibration, coupled to the OH in-plane
deformation, exhibits a moderate to strong band in the region
1250 ± 80 cmÀ1
[42]. The observed frequency at 1371 cmÀ1
in
FT-IR spectrum and 1380 cmÀ1
in FT-Raman spectrum and calcu-
lated wavenumber at 1387 cmÀ1
was identified CAO stretching
vibration coupled with COH in plane bending vibration shows good
agreement with experimental value. The C@O in-plane deformation
is weakly to moderately active in the region 725 ± 95 cmÀ1
. Most
carboxylic acids display cC@O in the region 595 ± 85 cmÀ1
which
is in the vicinity of that of methyl and ethyl esters [43]. The fre-
quency at 519 cmÀ1
in FT-IR spectrum and 521 cmÀ1
in FT-Raman
spectrum observed as OC@O in plane bending vibrations. This band
was calculated at 532 cmÀ1
by DFT method. The out of plane bend-
ing OC@O vibration observed at 633 cmÀ1
in FT-Raman spectra and
calculated at 631 cmÀ1
by DFT method. The hydroxyl stretching
vibrations are generally observed in the region 3400–3600 cmÀ1
[44]. In our molecule the computed wavenumber at 3302 cmÀ1
assigned OH symmetric stretching vibration of the carboxylic
group. The OH out-of-plane bending vibration gives rise to a band
in the region 700–600 cmÀ1
. The position of this band depends on
the strength of hydrogen bonding, the stronger the hydrogen bond
higher the wave number. In the present study CCOH torisional band
observed at 858 cmÀ1
in FT-IR spectrum and 894 cmÀ1
in FT-Raman
spectrum. The computed wavenumber at 859 and 862 cmÀ1
were
assigned CCOH torisional bending vibration.
CAN, CAC and CACAN group of vibrations
In L-phenylalanine-L-phenylalaninium dihydrogenphosphate,
CAN, vibration is identified at 1058 cmÀ1
[45]. In our title molecule
the band observed at 1059 cmÀ1
in FT-IR and 1056 cmÀ1
in
FT-Raman spectrum and computed wavenumber at 1062 cmÀ1
by DFT method identified as C-N stretching vibration. This mode
(mode no. 31) contributes 40% of the TED column. The CACAN in
plane bending vibrations (mode no’s: 48 51) observed at
519 cmÀ1
in FT-IR and 521 and 402 cmÀ1
in FT-Raman spectrum
and calculated at 532 and 404 cmÀ1
shows good agreement with
experimental findings. Also mode no’s 53 and 60 identified as
CACAN out of plane vibrations. Ravikumar et al. observed CAC
stretching bands at 878–977 cmÀ1
in L-phenylalanine-L-phenyla-
laninium dihydrogenphosphate [45]. In our title molecule CAC
stretching vibrations observed at 1093 cmÀ1
in FT-IR spectra and
1092 and 743 cmÀ1
in FT-Raman spectra. Theoretically computed
wavenumbers at 1186, 1086 and 794 cmÀ1
assigned tC1AC3,
tC3AC4 and tC4AC5 vibrations respectively.
CACl vibrations
The aliphatic CACl stretching bands absorb [46] at 830–
560 cmÀ1
and the substitution of chlorine on a carbon atom raises
the CACl wavenumber. In the present study CACl stretching band
observed at 602 cmÀ1
in FT-Raman spectrum. Theoretically
calculated wavenumber at 618 cmÀ1
by DFT method assigned CACl
stretching vibration, which is well correlate with experimental
value. The CACl in-plane bending and out-of plane bending vibra-
tions are assigned to the Raman bands at 238 and 116 cmÀ1
,
respectively. The computed wavenumbers at 243 and 148 cmÀ1
were assigned CACl in-plane and out-of plane bending vibrations
respectively. This is in agreement with the literature data [47–49].
Hydrogen bonding
Hydrogen bonds are very important dipole interactions in stabi-
lizing the protein structures. In amino acids having zwitterionic
form, the NH2 moiety is a good donor and the carboxyl group is
an excellent acceptor. The amino nitrogen of the phenylalanine
residue forms an OAHÁ Á ÁN hydrogen bond with O atom through
H of the carboxyl group. Olsztynska-Janus et al. [50] clearly
explained conformational structures of phenylalanine monomers,
their energies and dipole moments in the gas phase and they were
given Geometries of the seven lowest energy conformers of phen-
ylalanine, optimized by Gaussian 03 package at the B3LYP/6-31G*
level. The structure of our molecule 4CLPA is coinciding with
conformer1 (exception of para chloro substitution) of the phenylal-
anine given by S. Olsztynska-Janus et al. as shown in supplemen-
tary material S2. The title structure is stabilized by an
intramolecular hydrogen bond linking the carboxylic group to
the amino group and by hydrogen bonded interaction between
the amino hydrogen atoms and the p-electron system of the aro-
matic ring. The additional H-bonding interaction leads to increased
polarization of the amino group and the partial charge at the amino
hydrogen involved in the p-electron interaction with the phenyl
ring [51]. In the OAHÁ Á ÁN hydrogen bond, the bond length of
OAH is 0.994 Å, bond length of OÁ Á ÁN is 2.586 Å and bond angle
of OAHÁ Á ÁN is 126.2° calculated by b3lyp method [50]. The bond
lengths for strong, normal, and weak hydrogen bonds are 2.4–
2.7 Å, 2.7–2.9 Å, above 2.9 Å, respectively [52]. It will cause a
downshifting of stretching mode of vibrations and up shifting of
deformation modes [53]. The structure is stabilized by an extensive
network of OAHÁ Á ÁN hydrogen bonds. The NÁ Á ÁO distances remain
as 2.586 Å, shows strong hydrogen bonding. The hydrogen bonds
OAHÁ Á ÁN bond affects the various NH2 vibrational modes. The sym-
metric NH2 stretching is calculated at 3370 cmÀ1
this is 50 cmÀ1
down shifted from the expected range 3420–3340 cmÀ1
. The wag-
ging NH2 mode (mode no: 37) was most sensitive to hydrogen
bonding. The mode is 90 cmÀ1
higher than (up shift) expected
range 804 cmÀ1
considerably owing to the hydrogen bonding. Sim-
ilarly NH2 scissoring mode (mode no: 12) is identified 1599 cmÀ1
in FT-Raman spectrum which is around 70 cmÀ1
up shift from
the expected range1529–1650 cmÀ1
. The detailed assignment of
all observed hydrogen bonds is presented in Table 2. The same fea-
ture is also observed in L-phenylalanine phenylalanium nitrate [8],
dl-phenylalaninium nitrate [54] and L-leucine L-leucinium picrate
[55].
NBO analysis
The natural bond orbitals (NBO) calculations were performed
using NBO 3.1 program [56] as implemented in the Gaussian 03
package at the DFT/B3LYP level in order to understand various
second-order interactions between the filled orbitals of one
subsystem and vacant orbitals of another subsystem, which is a
measure of the intermolecular delocalization or hyper conjugation.
It is an essential tool for investigating charge transfer or conjuga-
tive interaction in molecular systems. Some electron donor orbital,
acceptor orbital and the interacting stabilization energy resulting
from the second-order micro disturbance theory is reported
[57,58]. The second-order Fock matrix was carried out to evaluate
the donor–acceptor interactions in the NBO analysis. The output
obtained by the 2nd-order perturbation theory analysis is normally
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810 805

8. the first to be examined by the experienced NBO user in searching
for significant delocalization effects. However, the strengths of
these delocalization interactions, E(2), are estimated by second
order perturbation theory [59] as estimated by Eq.
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 energy values for the interaction between the filled
(donors) i and vacant (acceptors) orbital j, calculated by the second
order perturbation theory have been tabulated Table 3. The larger
the E(2) value, the more intensive is the interaction between
electron donors and acceptors, i.e. the more the electrons donating
tendency from electron donors to acceptors. The energy involved
in hyperconjucative interactions in between carbon atoms in phe-
nyl ring p(C5AC10) ? p*
(C8AC9) is 21.96 kJ molÀ1
,
p(C5AC10) ? p*
(C6AC7) is 19.50 kJ molÀ1
. The other interaction
energy in this molecule is p electron donating from
p(C6AC7) ? p*
(C5AC10), p*
(C8AC9) and p(C8AC9) ? p*
(C6AC7),
p*
(C5AC10) resulting a stabilization energy of about 20.28, 20.16
and 19.46, 18.01 kJ molÀ1
respectively. The hyper conjugative
interaction and electron density transfer from lone electron pair
of the N2 atom to the O12AH23 antibonding orbital in the
O12AH23Á Á ÁN2 system has been predicted. This hydrogen bonding
is formed by the orbital overlap between n (LP1N2) and p*
(O12-
H23) which consequences intramolecular charge transfer (ICT)
causing stabilization of the hydrogen bonded system. Hence,
hydrogen bonding interaction leads to an increase in electron den-
sity of OAH antibonding orbital. Which is evident from the table
energy involved in the hyperconjugative interaction LP (1)
N2 ? p*
(O12AH23) is 15.12 kJ molÀ1
. Another most lonepair
interactions are LP(2)O11 ? r*
(C1AC3), r*
(C1AO12), LP(2)O12 ?
p*
(C1AO11) and LP(3)Cl13 ? p*
(C8AC9) resulting stabilization
energy of about 21.03, 32.93, 53.46 and 12.17 kJ molÀ1
. The
p*
(C8AC9) of the NBO conjugated with p*
(C5AC10) and
p*
(C6AC7) resulting to very much stabilization of 222.19 and
193.23 kJ molÀ1
respectively.
Static polarizability and first order hyperpolarizability
Quantum chemical calculations have been shown to be useful in
the description of the relationship between the electronic structure
of the systems and its NLO response [60]. The NLO activity provide
the key functions for frequency shifting, optical modulation, opti-
cal switching and optical logic for the developing technologies in
areas such as communication, signal processing and optical inter-
connections [61]. The polarizability (a) and the hyper polarizability
(b) and the electric dipole moment (l) of the 4-Chloro-DL-phenyl-
alanine are calculated by finite field method using HF/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 4CLPA.
In the presence of an applied electric field, the energy of a sys-
tem is a function of the electric field and the first hyperpolarizabil-
ity 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 [62]. 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 . . .
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 þ bxyy þ bxzzÞ
Table 3
Second order perturbation theory analysis of Fock Matrix in NBO basis for 4-Chloro-DL-phenylalanine.
Donor (i) ED (i)(e) Acceptor (j) ED (j)(e) E(2)a
kJ molÀ1
E(j) À E(i)b
a.u F(i,j)c
a.u
p(C5AC10) 1.661 p*
(C8AC9) 0.312 21.96 0.27 0.069
p*
(C6AC7) 0.381 19.50 0.28 0.067
p(C6AC7) 1.674 p*
(C5AC10) 0.349 20.28 0.28 0.068
p*
(C8AC9) 0.381 20.16 0.27 0.067
p(C8AC9) 1.682 p*
(C6AC7) 0.312 19.46 0.30 0.068
p*
(C5AC10) 0.349 18.01 0.30 0.066
LP(1)N2 1.919 p*
(O12AH23) 0.049 15.12 0.76 0.096
LP(1)O11 1.977 RY*
(1)C1 0.018 17.32 1.48 0.143
LP(2)O11 1.844 r*
(C1AC3) 0.092 21.03 0.59 0.101
r*
(C1AO12) 0.094 32.93 0.63 0.130
LP(2)O12 1.789 p*
(C1AO11) 0.227 53.46 0.33 0.120
LP(3)Cl13 1.931 p*
(C8AC9) 0.381 12.17 0.33 0.161
p*
(C8AC9) 0.381 p*
(C5AC10) 0.349 222.19 0.01 0.082
p*
(C6AC7) 0.312 193.23 0.01 0.079
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.
806 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810

9. by ¼ ðbyyy þ byzz þ byxxÞ
bz ¼ ðbzzz þ bzxx þ bzyyÞ
b ¼ ½ðbxxx þ bxyy þ bxzzÞ2
þ ðbyyy þ byzz þ byxxÞ2
þðbzzz þ bzxx þ bzyyÞ2
Š1=2
Since the values of the polarizabilities (a) and hyperpolarizability
(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 static polarizability ao and total polarizability Da of our
title molecule are 15.500 Â 10À24
esu and 9.813 Â 10À24
esu respec-
tively. The total molecular dipole moment and first order hyperpo-
larizability are 1.499 Debye and 1.005 Â 10À30
esu, respectively
and are depicted in Table 4. The calculated first order hyperpolariz-
ibility value is good agreement (1.38 Â 10À30
e.s.u.) with the
L-phenylalanine phenylalanium nitrate [8] also it is 2.69 times
greater than that of urea (b of urea are 1.3732 Debye and
0.3728 Â 10À30
esu obtained by HF/6-311G(d,p) method). This
result indicates the good nonlinearity of the title molecule.
Electronic properties
UV–Vis spectral analysis
The electronic absorption spectra of title molecule had been
measured in ethanol solvent at room temperature. To obtain some
electronic properties such as; the excitation energies, absorbance
and oscillator strengths for the 4CLPA molecule, we were opti-
mized geometry of the molecule in the ground state by using
TD-DFT calculations with the B3LYP/6-31G(d,p) method. In the
UV–Vis region with high extinction coefficients, all molecules
allow strong and r ? r*
and p ? p*
transition [63]. The calculated
absorption wavelengths (k), oscillator strengths (f), excitation
energies (E) are given Table 5. Experimentally observed UV–Vis
absorption spectrum of title molecule recorded in ethanol solvent
is presented in supplementary material S3. Typically, according
to the Frank–Condon principle, the maximum absorption peak kmax
in a UV–Vis spectrum corresponds to vertical excitation. Experi-
mentally, electronic absorption spectra of title molecule in ethanol
solvent showed two bands at 225 nm and 268 nm. The computed
UV method predicts one intense electronic transition at
224.40 nm with an oscillator strength f = 0.0295 a.u in ethanol sol-
vent and electronic transition at 233.31 nm with an oscillator
strength f = 0.0148 a.u in gas phase that shows good agreement
with measured experimental data k(exp) = 225 nm. The p ? p*
transitions were expected to occur relatively at lower wavelengths,
due to the consequence of the extended aromaticity of the benzene
ring, so the transition mainly corresponds to p ? p*
bands.
Frontier molecular orbitals
The analysis of the electronic transition indicates the transition
from the ground to the first excited state and is mainly described
by one-electron excitation from the highest occupied molecular
orbital (HOMO) to the lowest unoccupied orbital (LUMO). The
HOMO energy characterizes the ability of electron giving, whereas
the LUMO characterizes the ability of electron accepting, and the
gap between HOMO and LUMO characterizes the molecular chem-
ical stability. A molecule with a small frontier orbital gap is gener-
ally associated with a high chemical reactivity, low kinetic stability
and is also termed as soft molecule [64]. Energy difference
between HOMO and LUMO orbital is called as energy gap that is
an important stability for structures [65]. The energy gap between
HOMO and LUMO is a critical parameter in determining molecular
electrical transport properties [66]. In addition, according to
B3LYP/6-31G (d,p) calculation, the energy band gap of the 4CLPA
molecule is 5.983 eV shown in Fig. 4. The positive and negative
phase is represented in red and green color, respectively. The
region of HOMO and LUMO levels spread over the entire molecule
and the calculated energy gap of LUMO–HOMO’s explains the ulti-
mate charge transfer interface within the molecule.
HOMO energy ¼ À6:866 eV
LUMO energy ¼ À0:883 eV
HOMO À LUMO energy gap ¼ 5:983 eV
Natural population analysis
The natural atomic charges of 4CLPA calculated by natural pop-
ulation analysis by using the B3LYP/6-31G(d,p) method is pre-
sented in supplementary material S4. In all these compounds
among the ring carbon atoms C1 has a positive charge (0.814 e)
while others have negative charge. It may be the reason of the sub-
stitution of highly electronegative Oxygen atoms (O11O12). The
C8 carbon has less negative charge (À0.045 e) due to Cl substitu-
tion at the atom C8. The nitrogen atom N2 (À0.946 e) have the
highest negative charge as shown in the histogram supplementary
material S5. Reason for this high negative charge is an intra molec-
ular hydrogen bonding interaction occurs between the N2 atom
and H23 atom. O12 oxygen atom has the highest negative charge
(À0.709 e) when compare to another Oxygen atom O11
(À0.593 e). Natural Population Analysis shows that the H23 atom
has maximum positive atomic charges (0.515 e) than the other
hydrogen atoms. This is due to the presence of electronegative oxy-
gen atom (O12) in the carboxyl group as well as O12–H23Á Á ÁN2
intra molecular hydrogen bonded system.
Table 4
The electric dipole moment, polarizability and first order hyperpolarizability of 4-Chloro-DL-phenylalanine 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 0.013 axx 115.572 17.128 bxxx À48.250 À416.833
ly À0.034 axy 9.410 1.395 bxxy 25.018 216.129
lz 1.499 ayy 78.711 11.665 bxyy À20.379 À176.055
l 1.499 axz 30.909 4.581 byyy 13.327 115.134
ayz À19.924 À2.953 bxxz À47.609 À411.297
azz 119.491 17.709 bxyz À5.492 À47.4455
ao 104.591 15.500 byyz 8.890 76.8024
Da 66.216 9.813 bxzz À32.350 À279.475
byzz À14.284 À123.397
bzzz À13.906 À120.13
btot 116.383 1005.432
b = (1.005 Â 10À30
esu)
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810 807

10. Molecular electrostatic potential (MEP)
Molecular electrostatic potential have been found to be a very
useful tool in investigation of correlation between molecular struc-
tures with its physiochemical property relationship, including
biomolecules and drugs [67]. MEP map is very useful for the qual-
itative interpretation of the electrophilic and nucleophilic reactions
for the study of biological recognition process and hydrogen bond-
ing interactions [68].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 reac-
tions.MEP values were calculated using the equation [69]:
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
electronic density function of the molecule, and r0
is the dummy
integration variable. In the present study, molecular electrostatic
potential (MEP) of 4CLPA are illustrated in Fig. 5. The different val-
ues of the electrostatic potential at the surface are represented by
different colors. In the majority of the MEPs, while the maximum
negative region which preferred site for electrophilic attack indica-
tions as red color, the maximum positive region which preferred
site for nucleophilic attack symptoms as white color and blue
represents the region of zero potential. The color code of these maps
is in the range between À0.0409 a.u. (deepest red) and +0.0500 a.u.
(white) in our molecule. As can be seen from the MEP map of the
title molecule, while regions having the negative potential are over
the electronegative atom (oxygen atom) and Nitrogen atom, the
regions having the positive potential are over the hydrogen atoms.
The negative potential value is À0.0409 a.u. for oxygen atom. A
maximum positive region localized on the H atoms bond has value
of +0.0500 a.u. Blue color spread over the Cl atom and carbon atoms
of the phenyl ring these regions having partially negative charge.
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 [70,71]. On the
basis of EHOMO and ELUMO, these are calculated using the below
equations.
Using Koopman’s theorem for closed-shell molecules [72],The
hardness of the molecule is
g ¼ ðI À AÞ=2
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 4CLPA calculated by
B3LYP/6-31G (d,p) method is 0.883 eV and 6.866 eV respectively.
The calculated values of the Hardness, Softness, Chemical potential,
Table 5
The experimental and computed absorption wavelength k (nm), excitation energies E
(eV), absorbance and oscillator strengths (f) of 4-Chloro-DL-phenylalanine 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)
268 0.4220 237.06 5.2301 0.0074 239.72 5.1720 0.0076
225 3.6289 224.40 5.5251 0.0295 233.31 5.3143 0.0148
– – 215.02 5.7661 0.2325 219.80 5.6407 0.0215
LUMO Plot
(First excited state)
LUMO Energy = -0.8833 eV
Energy gap = 5.9831 eV
HOMO Energy = - 6.8664 eV
(Ground state)
HUMO Plot
Fig. 4. The atomic orbital compositions of the frontier molecular orbital for 4-Chloro-DL-phenylalanine.
808 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810

11. electronegativity and electrophilicity index of our molecule is 2.992,
0.167, À3.875, 3.875 and 2.509 respectively as shown in supple-
mentary material S6. Considering the chemical hardness, large
HOMO–LUMO gap represent a hard molecule and small HOMO–
LUMO gap represent a soft molecule.
NMR analysis
The 13
C and 1
H theoretical chemical shifts, isotropic shielding
tensors of 4CLPA with B3LYP/6-31G(d,p) basic set are presented
in Table 6. Aromatic carbons give signals in overlapped areas of
the spectrum with chemical shift values from 100 to 150 ppm
[73,74]. The chemical shift of C8 is greater than the other phenyl
carbon values. In the present work, 13
C NMR chemical shifts in
the ring for the title compound are 100 ppm, as they would be
expected. Due to the substitution of electronegative chlorine atom
in the benzene ring the chemical shift value of C8 is high
(131.0 ppm). The presence of electronegative atom attracts all elec-
tron clouds of carbon atoms towards the chlorine atom, which
leads to deshielding of carbon atom and net result in increase in
chemical shift value. The methyl and methylene groups are gener-
ally denoted as electron-donating groups, so they will be more
shielded. The methylene group carbon atom C4 is bonded to C5
carbon atom of the phenyl ring. Due to the electron donating nat-
ure of methylene group, the chemical shift of atom C5 is high
(128 ppm). Other four carbon peaks in the rings are calculated at
C6 (119.8 ppm), C7 (119.3 ppm), C9 (118.5 ppm) and C10
(121.0 ppm). Oxygen atom shows electronegative property there-
fore, the chemical shift value of C1 which is in the carboxylic group
has been observed at 163.2 ppm at DFT. The protons of phenyl ring
were calculated at 7.5 ppm, 7.3 ppm, 7.2 ppm and 7.2 ppm. The
characteristic down field signal at d11.6 ppm is attributed to the
proton (H23) of carboxylic moiety. The electronegative oxygen
atom (O12) present in the carbon atom (C1) deshields the proton
(H23) by means of an intramolecular hydrogen bonding of the type
O12–H23Á Á ÁN2 which reduces the electron density on H23 resulted
in downfield chemical shift. The hydrogen atoms H17 H18
attached with the methyl carbon of 4CLPA are in the same chemi-
cal environment and show two peaks at (C17) 2.8 ppm and (C18)
2.1 ppm. NH2 protons appear at 1.2, 4.18 and 1.3 ppm, for H14
and H15 respectively.
Conclusion
In the present work, the optimized molecular structure of the
stable conformer, electronic properties, FT-IR and FT-Raman Vibra-
tional frequencies and intensity of vibrations of the title compound
have been calculated by DFT method using B3LYP/6-31G(d,p) basis
set. Comparison of the experimental and calculated spectra of the
molecule showed that DFT-B3LYP method is in good agreement
with experimental data. The difference between the observed
and scaled wavenumber values of most of the fundamentals is very
small. Vibrational and NBO analysis confirms the formation of
hydrogen bond by the orbital overlap between LP and p*
which
results intramolecular charge transfer (ICT), results in stabilization
of the hydrogen bonded O12AH23Á Á ÁN2 system. The UV spectrum
was measured in ethanol solution and results are compared with
theoretical results. The HOMO–LUMO energies presented in this
work shows the presence of charge transfer within the molecule.
Molecular electrostatic potential map show possible sites for the
negative (red color) regions of MEP were related to electrophilic
reactivity and the positive (white color) ones to nucleophilic
reactivity. Energy gap of the title molecule is large 5.983 eV so
we conclude that our molecule is hard molecule, which is evident
from the value of chemical hardness is 2.6075 which is greater
than that of value of chemical softness is 0.1918. From the NLO
analysis, first order hyperpolarizability is 2.69 times greater than
that of urea. This result indicates the good nonlinearity of the title
molecule. Natural Population Analysis shows that the H23 atom
has maximum positive atomic charges (0.51493 e) than the other
hydrogen atoms. 1
H and 13
C NMR theoretical analysis was done
and the 1
H and 13
C NMR isotropic chemical shifts were calculated.
Acknowledgement
The authors are thankful to Dr. N. Sundaraganesan, Professor of
physics, Annamalai University, Tamilnadu, India for providing
Gaussian 03W facility.
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.2014.06.019.
References
[1] M.D. Aggarwal, J. Choi, W.S. Wang, K. Bhat, R.B. Lal, A.D. Shields, B.G. Penn, D.O.
Frazier, J. Cryst. Growth 204 (1999) 179–182.
[2] J. Shen, J.M. Zheng, Y.X. Che, B. Xi, J. Cryst. Growth 257 (2003) 136–140.
[3] F. Wang, J. Phys.: Conf. Ser. 141 (2008). 012019 1-9.
[4] M. Delfino, Mol. Cryst. Liq. Cryst. 52 (1979) 271–284.
[5] X. Cao, G. Fischer, J. Mol. Struct. 519 (2000) 153–163.
[6] S. Stewart, P.M. Fredericks, Spectrochim. Acta 55 (1999) 1641–1660.
[7] S.P. Vijaya Chamundeeswari, E. James Jebaseelan Samuel, N. Sundaraganesan, J.
Mol. Simul. (2012) 1–14.
[8] M. Amalanathan, I. Hubert Joe, V.K. Rastogi, J. Mol. Struct. 1006 (2011) 513–
526.
[9] E. Podstawka a, A. Kudelski, P. Kafarski, L.M. Proniewicz, J. Surface Sci. 601
(2007) 4586–4597.
[10] Ihsan M. Kenawi, Aladin H. Kamel, Rifaat H. Hilal, J. Mol. Struct. (THEOCHEM)
851 (2008) 46–53.
[11] P.A. Fantin, P.L. Barbieri, A. Canal Neto, F.E. Jorge, J. Mol. Struct. (THEOCHEM)
810 (2007) 103–111.
Fig. 5. Molecular electrostatic potential map of 4-Chloro-DL-phenylalanine calcu-
lated by B3LYP/6-31G(d,p) method.
Table 6
The predicted 1
H and 13
C NMR isotropic chemical shifts (with respect to TMS, all
values in ppm) for 4-Chloro-DL-phenylalanine.
Atom position B3LYP/6-31G(d,p) Atom position B3LYP/6-31G(d,p)
C1 163.2 H14 1.2
C3 53.6 H15 1.3
C4 34.7 H16 3.4
C5 128.0 H17 2.8
C6 119.8 H18 2.1
C7 119.3 H19 7.5
C8 131.0 H20 7.3
C9 118.5 H21 7.2
C10 121.0 H22 7.2
– – H23 11.6
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810 809

12. [12] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery, Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A.
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox,
H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.
Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y.
Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.
Dapprich, A.D. Daniels, M.C.Strain, O. Farkas, D.K. Malick, A D. Rabuck, K.
Raghavachari, J.B. Foresman, J.V. Ortiz, Q.Cui, A.G. Baboul, S. Clifford, J.
Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P.Piskorz, I. Komaromi, R.L.
Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A.Nanayakkara, M.
Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A.
Pople, Gaussian 03, Revision C.02, Gaussian Inc., Wallingford CT, 2004.
[13] M.H. Jamróz, Vibrational Energy Distribution Analysis VEDA 4, Warsaw, 2004.
[14] E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO Version 3.1, TCI,
Universityof Wisconsin, Madison, 1998.
[15] D.A. Kleinman, Phys. Rev. 126 (1962) 1977–1979.
[16] D. Michalska, R. Wysoki´nski, Chem. Phys. Lett. 403 (2005) 211–217.
[17] S. Shen, G.A. Guirgis, J.R. Durig, Struct. Chem. 12 (2001) 33–43.
[18] D. Michalska, RAINT, A computer program for calculation of Raman intensities
from the Gaussian outputs, Wrocław University of Technology, 2002.
[19] E.G. Lewars, Computational Chemistry, Springer Science, Business Media, B.V,
2011. pp. 1–7.
[20] R. Karpoormath, P. Govender, H.G. Kruger, T. Govender, G.E.M. Maguire, Acta
Cryst. E66 (2010) o2537–o2538.
[21] G.-X. Wang, Acta Cryst. (2010) E66. o50 ISSN 1600-5368.
[22] L.E. Sutton, Tables of Interatomic Distances, Chemical Society, London, 1958.
[23] P.B. Nagabalasubramanian, S. Periandy, S. Mohan, Spectrochim. Acta Part A 77
(2010) 150–159.
[24] V. Krishnakumar, V. Balachandran, T. Chithambarathanu, Spectrochim. Acta A
62 (2005) 918–925.
[25] V. Arjunan, S. Mohan, Spectrochim. Acta A 72 (2009) 436–444.
[26] E. Kavitha, N. Sundaraganesan, S. Sebastian, Ind. J. Pure Appl. Phys. 48 (2009).
[27] Y. Wang, S. Saebo, C.U. Pittman Jr., J. Mol. Struct.: (Theochem.) 281 (1993) 9l–
98.
[28] National Institute of Standards and Technology. Vibrational Frequency Scaling
Factors on the Web. http://srdata.nist.gov/cccbdb/vsf.asp (accessed
24.09.2007).
[29] N.P.G. Roeges, Wiley, New York, 1994.
[30] N. Sundaraganesan, H. Saleem, S. Mohan, M. Ramalingam, V. Sethuraman,
Spectrochim. Acta A 62 (2005) 740–751.
[31] N. Sundaraganesan, S. Ilakiamani, B.D. Joshua, Spectrochim. Acta A 67 (2007)
287–297.
[32] L.J. Bellamy, The Infrared Spectra of Complex Molecules, third ed., Wiley,
NewYork, 1975.
[33] T. Shimanouchi, Y. Kakiuti, I. Gamo, J. Chem. Phys. 25 (1956) 1245–1252.
[34] S. Sudha, N. Sundaraganesan, M. Kurt, M. Cinar, M. Karabacak, J. Mol. Struct.
985 (2011) 148–156.
[35] V. Krishnakumar, R.J. Xavier, T. Chithambarathanu, Spectrochim. Acta A62
(2005) 931–939.
[36] N.B. Colthup, L.H. Daly, S.E. Wiberly, Introduction to Infrared and Raman
Spectroscopy, third ed., Academic Press, Boston, 1990.
[37] R.M. Silverstein, G.C. Bassler, T.C. Morril, Spectrometric Identification of
Organic Compounds, fifth ed., John Wiley and Sons Inc., Singapore, 1991.
[38] Bismi. Edwin, I. Hubert Joe, J. Mol. Struct. 1034 (2013) 119–127.
[39] L.J. Bellamy, R.L. Williams, Spectrochim. Acta 9 (1957) 341–345.
[40] E.J. Baran, I. Viera, M.H. Torre, Spectrochim. Acta A. 66 (2007) 114–117.
[41] M. Gussoni, C. Castiglin, J. Mol. Struct. 521 (2000) 1–18.
[42] N.P.G. Roeges, A Guide to the Complete Interpretation of the Infrared Spectra
Of Organic Structures, Wiley, New York, 1994.
[43] Y. Shyma Mary, Y. Sheena Mary, Hema Tresa Varghesea, C. Yohannan Panicker,
P.J. Jojoa, Global J. Anal. Chem. 3 (2012) 1–14.
[44] D. Lin-Vien, N.B. Colthup, W.G. Fateley, J.G. Graselli, The Hand Book of Infrared
and Raman Characteristic Frequencies of Organic Molecules, Academic Press,
New York, 1991.
[45] B. Ravikumar, R.K. Rajaram, V. Ramakrishnan, J. Raman Spectrosc. 37 (2006)
597–605.
[46] N.B. Colthup, L.H. Daly, S.E. Wiberley, Introduction to Infrared and Raman
Spectroscopy, third ed., Academic Press, Boston, 1990.
[47] G. Varsanyi, Assignments for Vibrational Spectra of Seven Hundred Benzene
Derivatives, vol. 1–2, Adam Hilger, 1974.
[48] E.F. Mooney, Spectrochim. Acta 20 (1964) 1021–1032.
[49] E.F. Mooney, Spectrochim. Acta 19 (1963) 877–887.
[50] Sylwia Olsztynska-Janus, Katarzyna Szymborska, Malgorzata Komorowska,
Jozef Lipinski, J. Mol. Struct., Theochem 911 (2009) 1–7.
[51] K. Lee, J. Sung, K.J. Lee, S.K. Kim, Y.D. Park, Chem. Phys. Lett. 368 (2003) 262.
[52] I.D. Brown, Acta Cryst. A 32 (1976) 24–31.
[53] G.A. Jeffrey, W. Saenger, Hydrogen Bonding in Biological Structures, Springer-
Verlag, Berlin, Heidelberg, New York, 1991.
[54] M. Briget Mary, V. Sasirekha, V. Ramakrishnan, Spectrochim. Acta A 62 (2005)
446–452.
[55] Sameh Guidara, Habib Feki, Younes Abid, Spectrochim. Acta A 115 (2013) 437–
444.
[56] E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO Version 3.1
[57] C. James, A. AmalRaj, R. Reghunathan, I. Hubert Joe, V.S. JayaKumar, J. Raman
Spectrosc. 37 (2006) 1381–1392.
[58] L.J. Na, C.Z. Rang, Y.S. Fang, J. Zhejiang Univ. Sci. 6B (2005) 584–589.
[59] Haman Tavakkoli, Abolghasem Farhadipour, Arab. J. Chem., doi: http://
dx.doi.org/10.1016/j.arabjc.2011.05.001, in press.
[60] D.M. Burland, R.D. Miller, C.A. Walsh, Chem. Rev. 94 (1994) 31–75.
[61] V.M. Geskin, C. Lambert, J.L. Bredas, J. Am. Chem. Soc. 125 (2003) 15651–
15658.
[62] D.A. Kleinman, Phys. Rev. 126 (1977) 1962–1979.
[63] R.M. Silverstein, G.C. Bassler, T.C. Morrill, Spectrometric Identification of
Organic Compounds, John Wiley, Chichester, 1991.
[64] I. Fleming, Frontier Orbitals and Organic Chemical Reactions, John Wiley
Sons, New York, 1976.
[65] D.F.V. Lewis, C. Ioannides, D.V. Parke, Xenobiotica 24 (1994) 401–408.
[66] K. Fukui, Science 218 (1982) 747–754.
[67] E. Scrocco, J. Tomasi, Adv. Quantum Chem. 11 (1978) 115–121.
[68] B. Kosar, C. Albayrak, Spectrochim. Acta A 78 (2011) 160–167.
[69] P. Politzer, J.S. Murray, Theor. Chem. Acc. 1087 (2002) 134–142.
[70] R. Parr, L. Szentpaly, S. Liu, Am. Chem. Soc. 121 (1999) 1922–1924.
[71] P. Chattraj, B. Maiti, U. Sarkar, J. Phys. Chem. A107 (2003) 4973–4975.
[72] T.A. Koopmans, Physica 1 (1934) 104–113.
[73] H.O. Kalinowski, S. Berger, S. Braun, Carbon-13 NMR spectroscopy, John Wiley
Sons, Chichester, 1988.
[74] K. Pihlaja, E. Kleinpeter (Eds.), Carbon-13 Chemical Shifts in Structural and
Sterochemical Analysis, VCH Publishers, Deerfield Beach, 1994.
810 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 799–810