The document reports on a study investigating the geometrical optimization, spectroscopic analysis, electronic structure, and nuclear magnetic resonance of (S)-(−)-N-(5-Nitro-2-pyridyl) alaninol (SN5N2PLA) using density functional theory calculations. The Fourier transform infrared and Raman spectra were recorded and vibrational assignments were analyzed. Ultraviolet-visible spectra were also recorded and electronic properties like HOMO-LUMO energies were calculated. Nuclear magnetic resonance chemical shifts were calculated and compared to experimental data. The first hyperpolarizability and other properties were computed to investigate the compound's potential as a nonlinear optical material.

1. Vibrational spectra, molecular structure, NBO, NMR, UV, first order
hyperpolarizability, analysis of (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol
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
SN5N2PLA were reported.
The first order hyperpolarizability
was calculated.
UV–Vis spectra were recorded and
compared with calculated values.
1
H and 13
C NMR spectra were
recorded and analyzed.
g r a p h i c a l a b s t r a c t
Optimized molecular structure of (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol.
a r t i c l e i n f o
Article history:
Received 6 November 2013
Received in revised form 30 January 2014
Accepted 16 February 2014
Available online 4 March 2014
Keywords:
NBO
UV–Vis
NMR
Hyperpolarizability
(S)-(À)-N-(5-Nitro-2-pyridyl) alaninol
a b s t r a c t
In this study, geometrical optimization, spectroscopic analysis, electronic structure and nuclear magnetic
resonance studies of (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol (abbreviated as SN5N2PLA) were investigated
by utilizing HF and DFT/B3LYP with 6-31G(d,p) as basis set. The Fourier transform infrared (FT-IR) and
FT-Raman spectra of SN5N2PLA were recorded in the region 4000–400 cmÀ1
and 3500–50 cmÀ1
, respec-
tively. Complete vibrational assignments, analysis and correlation of the fundamental modes for the title
compound were carried out. UV–Visible spectrum of the compound that dissolved in methanol were
recorded in the region 200–800 nm and the electronic properties HOMO and LUMO energies were mea-
sured by TD-DFT approach. The calculated HOMO and LUMO energies show that charge transfer occurs
within the molecule. The molecular stability and bond strength have been investigated by applying
the Natural Bond Orbital (NBO) analysis. The 1
H and 13
C nuclear magnetic resonance (NMR) chemical
shifts of SN5N2PLA were calculated using the GIAO method in methanol solution and compared with
the measured experimental data. The dipole moment, polarizability and first order hyperpolarizability
values were also computed. The polarizability and first hyperpolarizability of the studied molecule indi-
cate that the compound is a good candidate of nonlinear optical materials. The Chemical reactivity and
Thermodynamic properties of SN5N2PLA at different temperature are calculated. In addition, molecular
electrostatic potential (MEP), frontier molecular orbitals (FMOs) analysis were investigated using theo-
retical calculations.
Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.saa.2014.02.107
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 127 (2014) 498–510
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa

2. Introduction
The organic molecules exhibiting nonlinear optical (NLO) prop-
erties have been motivated by their potential for applications in
optical communications, optical computing, data storage, dynamic
holography, harmonic generators, frequency mixing, and optical
switching [1,2]. The advantages of using organic molecules as
NLO materials are that they can be designed to optimize the de-
sired NLO property by having different donor and acceptor groups
in the molecules. At the molecular level, compounds are expected
to exhibit large values of molecular hyperpolarizability (b) if they
possess polarizable electrons, for example, p-electrons spread over
a larger distance. It has been reported that extended p conjugated
systems with terminal donor–acceptor substituents to exhibit
large b values [3,4]. The nitropyridine derivatives are particularly
interesting because they form an acceptor fragment of 2-adaman-
tylamino-5-nitropyridine (AANP), which showed a very large non-
linearity among the materials reported earlier [5]. Marchewka
et al. [6] reported Crystal and molecular structure of N-(4-
nitrophenyl)-b-alanine-its vibrational spectra and theoretical
calculations. Kanetake et al. [7] reported Extractive spectrophoto-
metric determination of palladium with Di-2-pyridylmethanone
2-(5-Nitro) pyridylhydrazone. Kohatha et al. [8] reported synthesis
and chromogenic properties of some water-soluble 5-Nitro-2-pyri-
dilhydrozones. Chan-il Park et al. [9] reported spectrophotometric
determination of copper after selective extraction with a-(2-
Benzimidazolyl) a0
-a00
-(N-5-nitro-2-pyridyl hydrazone)-toluene.
To the best of our knowledge, neither quantum chemical calcu-
lation, nor the vibrational spectra of SN5N2PLA have been re-
ported. The present work mainly deals with experimental FT-IR
and FT-Raman spectra, vibrational assignments using total energy
distribution (TED) and NLO activity as well as HF and DFT/B3LYP
calculations for SN5N2PLA. In addition, the first order hyperpolar-
izability, NMR analysis and UV spectral analysis of SN5N2PLA
have been investigated. The theoretically predicted values have
been compared with the experimentally measured data and also
the results have been discussed. Nowadays NIR–FT-Raman spec-
troscopy combined with quantum chemical computations has
been recently used as an effective tool in the vibrational analysis
of drug molecules [10], biological compounds [11] and natural
products [12]. Since fluorescence-free Raman spectra and the
computed results can help unambiguous identification of vibra-
tional modes as well as the bonding and structural features of
complex organic molecular systems. HOMO–LUMO analysis have
been performed by applying density functional theory calcula-
tions based on B3LYP with 6-31G(d,p) as basis set. We have also
performed NBO calculation to provide a convenient basis for
investigating charge transfer or conjugative interaction in molec-
ular systems.
Experimental details
The compound (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol in the so-
lid form was purchased from TCI INDIA chemical company at
Chennai, with a stated purity greater than 98% and it was used
as such without further purification. The FT-IR spectrum of this
compound was recorded in the range of 4000–400 cmÀ1
on a
Perkin Elmer FT-IR spectrometer using KBr pellet technique. The
spectrum was recorded in the room temperature, with scanning
speed of 10 cmÀ1
. FT-Raman spectrum of the title compound was
recorded using 1064 nm line of Nd:YAG laser as excitation wave-
length 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 SN5N2PLA were examined in
the range 200–800 nm using Cary 5EUV–VIS–NIR spectrometer.
The UV pattern is taken from a 10–5 M solution of SN5N2PLA, dis-
solved in methanol. NMR spectra are recorded on Bruker AVANCE
III 500 MHz (AV 500) spectrometer; chemical shifts are expressed
in ppm (d units) relative to TMS signal as internal reference in
methanol. 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 spectral
measurements were 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 SN5N2PLA
in the present work. All the calculations were performed using
Gaussian 03W program package [13] with the default convergence
criteria without any constraint on the geometry [14]. The assign-
ments of the calculated wavenumbers are aided by the animation
option of Gauss View 3.0 graphical interface for Gaussian
programs, which gives a visual presentation of the shape of the
vibrational modes along with available related molecules [15]. Fur-
thermore, theoretical vibrational spectra of the title compound
were interpreted by means of TED using the VEDA 4 program
[16]. The optimized structural parameters were used in the vibra-
tional frequency calculations at DFT levels to characterize all sta-
tionary points as minima. As the hybrid B3LYP functional tends
to overestimate the fundamental normal modes of vibration, the
computed frequencies were scaled with appropriate values to
bring harmonization between the theoretical and experimental
wavenumbers [17]. Vibrational frequencies were computed at
DFT level which had reliable one-to-one correspondence with
experimental IR and Raman frequencies [18]. 1
H and 13
C NMR
chemical shifts were calculated with GIAO approach [19,20] by
applying B3LYP method [21,22]. The Natural Bond Orbital (NBO)
calculations were performed using NBO 3.1 program [23] as imple-
mented in the Gaussian 03W [13] package at the DFT/B3LYP level;
in order to understand various second order interactions between
filled orbital of one subsystem and vacant orbital of another sub-
system, which is a measure of the intermolecular delocalization
or hyper conjugation.
Prediction of Raman intensities
The Raman activities (SRa) calculated with Gaussian 03 program
[13] converted to relative Raman intensities (IRa) using the follow-
ing relationship derived from the intensity theory of Raman scat-
tering [24,25]
Ii ¼
fðvo À viÞ4
Si
vi½1 À expðÀhcvi=ktÞŠ
Where m0 is the laser exciting wavenumber in cmÀ1
(in this work,
we have used the excitation wavenumber m0 = 9398.5 cmÀ1
, which
corresponds to the wavelength of 1064 nm of a Nd-YAG laser), mi
the vibrational wavenumber of the ith normal mode (cmÀ1
) while
Si is the Raman scattering activity of the normal mode mi. f (is a con-
stant equal to 10À12
) is a suitably chosen common normalization
factor for all peak intensities. h, k, c and T are Planck and Boltzmann
constants, speed of light and temperature in Kelvin, respectively.
For the simulation of calculated FT-Raman spectra have been plot-
ted using pure Lorentizian band shape with a bandwidth of Full
Width at Half Maximum (FWHM) of 10 cmÀ1
.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510 499

3. Results and discussion
Conformational stability
In order to describe conformational flexibility of the title mole-
cule, the energy profile as a function of (N2–C3–C4–H21) and (N2–
C3–C1–O5) torsion angles were achieved with B3LYP/6-31G(d,p)
method. Potential energy surface (PES) scan in N2–C3–C4–H21
and N2–C3–C1–O5 dihedral angles was performed. The scan was
carried out by minimizing the potential energy in all geometrical
parameters by changing the torsion angle every 10° for 180° rota-
tion around the bond. The shape of the potential energy as a func-
tion of the dihedral angles are illustrated in supplementary
material S1. The conformational energy profile shows two maxima
near 180° and 300° for N2–C3–C4–H21 torsion angle. The maxi-
mum energies are obtained À638.9988 and À567.2617 Hartree
for 180° and 300° respectively. It is clear from supplementary
material S1, there are two local minima (stable conformers) ob-
served at 0° or 360° having the energy of À701.2153 Hartree and
240° having the energy of À701.1502 Hartree for T (N2–C3–C4–
H21). Similarly one maximum energy is obtained at 170° having
the energy À700.144 Hartree and one local minima (stable
conformers) observed at 0° or 360° having the energy
À701.279 Hartree for dihedral angle T (N2–C3–C1–O5). Therefore,
the most stable conformer is for 0° torsion angle for (N2–C3–C4–
H21) and (N2–C3–C1–O5) rotation. Further results are based on
the most stable conformer of SN5N2PLA molecule to clarify molec-
ular structure and assignments of vibrational spectra.
Molecular geometry
The optimized geometric parameters such as bond lengths,
bond angles and dihedral angles of the title molecule were given
in Table 1 using HF and density functional theoretical calculation
with 6-31G(d,p) basis set. The atom numbering scheme adopted
in this study is given in Fig. 3. Owing to the absence of experimen-
tal data the title molecule is compared with XRD data of closely re-
lated molecule 2-Amino-5-nitropyridinium tetraoxidorhenate(VII)
monohydrate [26]. From the theoretical values we found that most
of the optimized bond lengths and bond angles are slightly smaller,
as well as longer than the experimental values in both HF and DFT
levels. This is due to fact that the theoretical calculations belong to
isolated molecule in gaseous phase and experimental results
belong to molecule in solid state. The optimized bond length of
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm-1)
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm-1
)
Transmittance(%)IRintencity(arb.units)
Fig. 1. Comparison of theoretical B3LYP/6-31G(d,p) 1(a) and experimental 1(b) FT-IR spectra for (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol.
500 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

4. C–C in the molecule fall in the range 1.381–1.538 Å at B3LYP and
1.368–1.527 Å at HF methods shows good agreement with re-
corded X-ray data of 1.360–1.413 Å. The optimized bond lengths
of C–N in the molecule fall in the range 1.328–1.467 Å at B3LYP
and 1.313–1.459 Å at HF methods are very close to recorded
X-ray data of 1.341–1.446 Å. The optimized bond lengths of C–H
in the molecule fall in the range 1.083–1.102 Å at B3LYP and
1.071–1.089 Å at HF methods are clearly coincide with observed
X-ray data of 0.930 Å. The average N–O distance of 1.234 Å in the
nitro group is an indication of clearly double bonds. The bond angle
O13–N12–O14 (124.5°) of nitro group at both B3LYP and HF meth-
ods which is closer to experimental data (123.3 Å). The bond angle
between nitrogen of the pyridine ring and nitrogen of the NH
group N2–C6–N11 (114.4°) at B3LYP method and (114.8°) at HF
method which is smaller than the experimental finding (119.2°).
The dihedral angles are calculated according to the atoms N2–
C6–C7–C8 (À179.42°) at B3LYP method and (179.99°) at HF
method and C7–C8–C9–N12 (À179.97°) at B3LYP method and
(À179.95°) at HF method which is good agreement with experi-
mental data at (À179.9°) and (179.5°).
Vibrational assignments
Density functional theory is known for good performance in the
estimation of vibrational spectra of organic compounds, and it can
be observed in the molecule SN5N2PLA.The combined FTIR and FT–
Raman spectra of the title compound under investigation are
shown in Figs. 1 and 2. The observed and calculated frequencies
using HF/6-31G(d,p) and B3LYP/6-31G(d,p) basis set and along
with their relative intensities, 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.
According to the theoretical calculations, SN5N2PLA has structure
of C1 point group symmetry. The molecule has 25 atoms and 69
normal modes of vibrations. Theoretically all the fundamental
vibrations are active in both IR and Raman. The results showed that
the HF and DFT (B3LYP) methods applied in this work leads to
vibrational wavenumbers which are in good agreements with the
experimental data. The small difference between the experimental
and calculated vibrational modes could be attributed to the fact
3500 3000 2500 2000 1500 1000 500
Wavenumber (cm-1
)
3500 3000 2500 2000 1500 1000 500
Wavenumber (cm-1
)
Ramanintensity(arb.units)Ramanintensity(arb.units)
Fig. 2. Comparison of theoretical B3LYP/6-31G(d,p) 2(a) and experimental 2(b) FT-IR spectra for (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510 501

5. that the experimental results belong to solid phase while the the-
oretical belong to isolated gaseous phase. The calculated vibra-
tional frequencies were scaled in order to improve the agreement
with the experiment values. In our study we have followed scaling
factor of 0.9026 for HF/6-31G(d,p) and 0.9608 for B3LYP/6-
31G(d,p) respectively. After scaling with a scaling factor [27], 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 values
reveals that the 6-31G(d,p) basis set result shows very good
agreement with experimental observations, even for a complex
molecular system.
O–H vibrations
The O–H stretching vibrations normally appear around
3600 cmÀ1
as in phenol [28]. Bands due to O–H stretching are of
medium to strong intensity in the infrared spectrum, although it
may be broad. In Raman spectra the band is generally weak. Unas-
sociated hydroxyl groups absorbs strongly in the region 3670–
3580 cmÀ1
. For solids, liquids and concentrated solutions a broad
band of less intensity is normally observed [29]. In our case O–H
stretching vibration observed at 3656 cmÀ1
at B3LYP method and
3773 cmÀ1
HF method, and no O–H stretching bands observed in
the experimental methods as shown in Table 2. The TED corre-
sponding to this vibration is a pure stretching mode and it is
Table 1
Calculated optimized parameter values of the (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol [Bond length in (Å), angles in (°)].
Bond length B3LYP HF Expa
Bond angle B3LYP HF Expa
Dihedral angle B3LYP HF Expa
C1–C3 1.538 1.527 – C3–C1–O5 112.6 112.2 – O5–C1–C3–N2 57.50 58.40 –
C1–O5 1.417 1.397 – C3–C1–H15 109.3 109.5 – O5–C1–C3–C4 À179.86 À179.18 –
C1–H15 1.102 1.089 – C3–C1–H16 109.3 109.5 – O5–C1–C3–H18 À60.26 À60.03 À
C1–H16 1.095 1.084 – O5–C1–H15 111.5 111.1 – H15–C1–C3–N2 À66.94 À65.45 –
N2–C3 1.467 1.459 – O5–C1–H16 106.4 106.7 – H15–C1–C3–C4 55.71 56.97 –
N2–C6 1.369 1.358 1.313 H15–C1–H16 107.7 107.7 – H15–C1–C3–H18 175.30 176.13 –
N2–H17 1.013 0.996 0.890 C3–N2–C6 126.4 126.6 – C16–C1–C3–N2 175.49 176.67 –
C3–C4 1.531 1.527 – C3–N2–H17 117.0 116.8 – C16–C1–C3–C4 À61.87 À60.91 –
C3–H18 1.096 1.084 – C6–N2–H17 112.1 112.2 – C16–C1–C3–H18 57.73 58.24 –
C4–H19 1.093 1.084 – C1–C3–N2 110.9 110.9 – C3–C1–O5–H22 À67.92 À71.61 –
C4–H20 1.094 1.085 – C1–C3–C4 111.4 111.3 – H15–C1–O5–H22 55.28 51.35 –
C4–H21 1.096 1.087 – C1–C3–H18 107.8 108.0 – H16–C1–O5–H22 172.38 168.49 –
O5–H22 0.967 0.944 – N2–C3–C4 109.8 109.7 – C6–N2–C3–C1 À101.60 À104.93 –
C6–C7 1.418 1.410 1.413 N2–C3–H18 107.8 108.2 – C6–N2–C3–C4 134.82 131.72 –
C6–N11 1.353 1.332 1.358 C4–C3–H18 109.0 108.6 – C6–N2–C3–H18 16.20 13.33 –
C7–C8 1.381 1.368 1.351 C3–C4–H19 111.0 110.8 – H17–N2–C3–C1 104.21 100.66 –
C7–H23 1.083 1.071 0.930 C3–C4–H20 110.6 110.6 – H17–N2–C3–C4 À19.38 À22.68 –
C8–C9 1.399 1.391 1.402 C3–C4–H21 111.0 111.1 – H17–N2–C3–H18 À138.00 À141.07 –
C8–H24 1.083 1.072 0.930 H19–C4–H20 108.2 108.2 – C3–N2–C6–C7 21.95 21.74 –
C9–C10 1.396 1.382 1.360 H19–C4–H21 108.3 108.3 – C3–N2–C6–N11 À159.38 À159.68 –
C9–N12 1.451 1.438 1.446 H20–C4–H21 107.6 107.8 – H17–N2–C6–C7 177.22 177.12 –
C10–N11 1.328 1.313 1.341 C1–O5–H22 107.1 109.2 – H17–N2–C6–N11 À4.11 À4.30 –
C10–H25 1.085 1.073 0.930 N2–C6–C7 123.0 123.0 122.8 C1–C3–C4–H19 176.64 177.07 –
N12–O13 1.234 1.196 1.216 N2–C6–N11 114.4 114.8 119.2 C1–C3–C4–H20 56.52 57.02 –
N12–O14 1.234 1.196 1.217 C7–C6–N11 122.5 122.2 118.0 C1–C3–C4–H21 À62.84 À62.59 –
C6–C7–C8 118.3 118.2 120.0 N2–C3–C4–H19 À60.11 À59.86 –
C6–C7–H23 120.6 121.0 120.0 N2–C3–C4–H20 179.77 À179.90 –
C8–C7–H23 121.0 120.8 120.0 N2–C3–C4–H21 60.41 60.48 –
C7–C8–C9 118.7 118.8 118.9 H18–C3–C4–H19 57.74 58.29 –
C7–C8–H24 121.8 121.2 120.6 H18–C3–C4–H20 À62.38 À61.75 –
C9–C8–H24 119.5 120.0 120.6 H18–C3–C4–H21 178.26 178.63 –
C8–C9–C10 119.4 119.1 121.3 N2–C6–C7–C8 À179.42 179.99 À179.9
C8–C9–N12 120.4 120.5 120.1 N2–C6–C7–H23 3.60 2.54 –
C10–C9–N12 120.2 120.3 118.6 N11–C6–C7–C8 2.02 1.52 À0.1
C9–C10–N11 122.7 122.5 118.5 N11–C6–C7–H23 À174.96 À175.93 –
C9–C10–H25 119.8 120.3 120.7 N2–C6–N11–C10 À180.00 À179.61 179.9
N11–C10–H25 117.5 117.2 120.7 C7–C6–N11–C10 À1.32 À1.02 0.1
C6–N11–C10 118.4 119.1 123.2 C6–C7–C8–C9 À0.90 À0.64 À0.2
C9–N12–O13 117.7 117.7 117.7 C6–C7–C8–H24 179.99 À179.90 –
C9–N12–O14 117.8 117.9 119.0 H23–C7–C8–C9 176.07 176.81 –
O13–N12–O14 124.5 124.5 123.3 H23–C7–C8–H24 À3.04 À2.44 –
C7–C8–C9–C10 À0.77 À0.63 0.4
C7–C8–C9–N12 À179.97 À179.95 179.5
H24–C8–C9–C10 178.36 178.64 –
H24–C8–C9–N12 À0.84 À0.69 –
C8–C9–C10–N11 1.54 1.19 À0.4
C8–C9–C10–H25 À178.84 À179.19 –
N12–C9–C10–N11 À179.26 À179.49 À179.5
N12–C9–C10–H25 0.36 0.14 –
C8–C9–N12–O13 À0.47 À0.61 1.0
C8–C9–N12–O14 179.56 179.43 À177.2
C10–C9–N12–O13 À179.66 À179.92 À179.9
C10–C9–N12–O14 0.37 0.12 1.9
C9–C10–N11–C6 À0.48 À0.35 0.1
H25–C10–N11–C6 179.89 180.01 –
a
Taken from Ref. [26].
502 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

6. exactly contributing to 100%. Some researchers [30,31] have as-
signed C–OH stretching mode around 1200 cmÀ1
in substituted
benzenes and pyridines. The C–OH in-plane bending mode ob-
served at 1184 cmÀ1
in experimental FT Raman spectrum and
1036 cmÀ1
in FTIR spectrum. C–OH in-plane bending vibration also
calculated in 1178 cmÀ1
at B3LYP method and 1180 cmÀ1
at HF
method shows good agreement with experimental observations.
The O–H in-plane bending vibration for phenyl, in general lies in
the region 1150–1250 cmÀ1
and it is not much affected due to
hydrogen bonding unlike that of stretching and out-of-plane bend-
ing wavenumber [32]. For our molecule, the O–H Out of plane
bending vibration appears in theoretically computed wavenum-
bers at 894 cmÀ1
in B3LYP and 903 cmÀ1
in HF methods. The TED
corresponding to this vibration suggests that it is a weak mode
and exactly contributing to 29%. This band is experimentally ob-
served at 883 cmÀ1
in FTIR spectrum.
N–H vibrations
The N–H stretching modes of secondary amides are generally
observed in the region of 3460–3300 cmÀ1
for N–H stretching and
a weak band at 3100–3070 cmÀ1
for an overtone of the N–H band
[33]. For the title compound, the very strong band observed at
3252 cmÀ1
in the IR spectrum is assigned as N–H stretching mode.
The calculated wavenumber for this mode is at 3456 cmÀ1
in B3LYP
method and 3480 cmÀ1
in HF method. This mode is a pure stretch-
ing mode, and as it is evident from the TED column they are almost
contributing 100%. The wavenumber (3456 cmÀ1
) computed by
B3LYP/6-31G(d,p) method shows the deviation (204 cmÀ1
) when
compared with experimental IR data (3252 cmÀ1
). This may be
due to intermolecular hydrogen bonds in solid state between the
NH group and the pyridine N atom. This is the reason for the down-
shift of NH band at 3252 cmÀ1
.
The weak N–H in-plane bending mode observed at 1405 cmÀ1
in FTIR spectrum and 1329 and 1504 cmÀ1
in FT-Raman spectrum.
The calculated wavenumber for this mode is at 1419 cmÀ1
at
B3LYP method and 1465 cmÀ1
at HF method. The out of plane
bending vibration observed at 922 cmÀ1
in FTIR spectrum. The cal-
culated wave number for this mode is at 942 and 944 cmÀ1
in
B3LYP method and 954 and 1002 cmÀ1
in HF method. Theoretically
predicted values are coinciding very well with the observed fre-
quencies. The TED corresponding to this vibration suggests that it
(mode. No. 40) is a medium mode and exactly contributing to 73%.
C–H vibrations
The hetero aromatic structure shows the presence of C–H
stretching vibrations in the range of 3100–3000 cmÀ1
[34] which
is the characteristic region for the ready identification of C–H
stretching vibrations, and the bands are not affected by the nature
of substitutions. In the present study the C–H stretching band
observed at 2939 and 3073 cmÀ1
in FT-Raman spectrum. The com-
puted wavenumbers for these modes are at 2919, 3073, 3076 and
3090 cmÀ1
in HF method and 2941, 3089, 3105 and 3117 cmÀ1
in
B3LYP method assigned C–H stretching vibrations.
The C–H in-plane bending vibrations normally occur as a num-
ber of strong-to-weak intensity sharp bands in the region 1300–
1000 cmÀ1
[35,36]. In our molecule the C–H in plane bending
vibrations are observed at 1101 and 1294 cmÀ1
in FTIR spectrum
1184, 1295, 1329, and 1351 cmÀ1
in FT-Raman spectrum. The cal-
culated wavenumbers at 1419, 1281, 1101, 1178, 1325 and
1348 cmÀ1
in B3LYP method and 1119, 1180, 1319, 1304 and
1401 cmÀ1
in HF level assigned to C–H in plane bending vibrations.
Swaminathan et al. assigned C–H out of plane bending modes in
the region 1405 cmÀ1
[37]. In our case the C–H out of plane vibra-
tions are observed in 1405 cmÀ1
in FTIR spectrum. The calculated
wave numbers for this mode at 1377 and 1419 cmÀ1
in B3LYP level
and 1417 and 1465 cmÀ1
HF level assigned to C–H out of plane
bending vibrations. The TED corresponding to this vibration sug-
gests that it (mode. No. 19) is a medium mode and exactly contrib-
uting to 41%.
C–C vibrations
Carbon–carbon ring stretching vibrations occur in the region
1430–1625 cmÀ1
. In general, the bands are of variable intensity
and are observed at 1625–1590, 1575–1590, 1470–1540, 1430–
1465 and 1280–1380 cmÀ1
from the wavenumber ranges given
by Varsanyi [36] for the five bands in the region. The (C–C) stretch-
ing modes are normally observed in the range 1650–1400 cmÀ1
in
benzene derivatives [38]. In the present molecule the peaks ob-
served at 1405 cmÀ1
in FT-IR spectrum and 858, 1148, 1504,
1583 cmÀ1
in FT-Raman spectrum are assigned to C–C stretching
vibrations. The calculated wavenumber for this vibrational mode
is at 854, 1146, 1502 and 1582 cmÀ1
at B3LYP method and 872,
1167, 1538 and 1623 cmÀ1
at HF method are assigned to C–C
stretching vibrations. The C–C–C bending bands always occur be-
low 600 cmÀ1
[38]. In the present work, the computed values at
198, 285, 621, 664, 793, 986 cmÀ1
in B3LYP level and at 199, 292,
628, 675, 809 and 1022 cmÀ1
in HF method are assigned C–C–C
in-plane bending vibrations. The bands observed at 622 and
697 cmÀ1
in FT-IR spectrum and 637 cmÀ1
in FT-Raman spectrum
in our molecule is assigned to C–C–C in-plane bending vibration.
C–N vibrations
The identification of C–N stretching vibrations is a very difficult
task, since the mixing of several bands is possible in this region.
However, with the help of the animation option of Gauss View
3.0 graphical interface for Gaussian programs and TED value from
VEDA 4 program, the C–N stretching vibrations are identified and
assigned in this study. The C–N stretching vibrations are always
Fig. 3. Optimized molecular structure and atomic numbering of (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510 503

7. Table 2
Comparison of the experimental and calculated vibrational spectra and proposed assignments of (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol.
Mode nos. Experimental wavenumbers/cmÀ1
Theoretical wavenumbers/cmÀ1
Vibrational assignments with TED (P10%)
HF/6-31G(d,p) B3LYP/6-31G(d,p)
FT-IR FT-Raman Unscaled Scaled IIR
a
IRa
b
Unscaled Scaled IIR
a
IRa
b
1 4180 3773 46.88 7.96 3805 3656 18.57 28.54 tO5H22(100)
2 3252 3855 3480 59.80 15.25 3597 3456 48.66 58.88 tN2H17(100)
3 3423 3090 1.82 19.08 3244 3117 1.47 34.76 tCH(95) py.ring breathing
4 3408 3076 0.10 10.41 3231 3105 0.19 19.57 tCH(95) ass.str in py.ring
5 3073 3404 3073 0.76 14.59 3215 3089 0.60 3.99 tCH(99) sym.str py.ring
6 3273 2954 34.82 21.31 3137 3014 19.24 5.5 tCH(99) ass.str in CH3
7 3263 2945 76.86 29.1 3119 2997 29.77 6.91 tCH(92) ass.str in CH3
8 3248 2931 8.88 4.19 3095 2973 29.76 7.12 tCH(88) ass.str in CH2
9 2939 3234 2919 7.00 15.66 3061 2941 11.18 1.63 tCH(90) sym str. C3H18
10 3185 2875 37.59 36.49 3046 2927 17.51 9.97 tCH(94) breathing in CH3
11 2801 3166 2858 49.80 15.49 2994 2876 58.90 7.21 tCH(92) sym str.in CH2
12 1851 1670 571.88 0.73 1656 1591 374.26 5.16 tCC(55) py.ring + tassON(15)
13 1583 1798 1623 447.30 83.69 1646 1582 285.42 4.11 tCC(71) py.ring + tassON(12)
14 1761 1590 42.80 1.49 1597 1534 30.96 0.42 tCC(63) py.ring + tassON(47)
15 1504 1704 1538 229.43 3.15 1563 1502 273.71 2.8 tCC(12) py.ring + dHCC(14) py.ring
16 1481 1460 1642 1482 24.36 5.55 1515 1456 4.02 2.37 dHCH(71) in CH3 + dH19C4C3C1 (14)
17 1458 1634 1474 207.26 100 1513 1454 8.15 2.9 dHCH(71) in CH2 + dH19C4C3C1 (18)
18 1627 1469 143.03 53.7 1507 1448 1.00 0.14 dHCH(72) sci in CH2
19 1405 1623 1465 60.10 27.72 1477 1419 5.45 7.66 tCC(15) in py ring + dH17N2C6 (27)+dHCC(11) in pyr.ring + cC3H18C4H19(41)
20 1607 1450 343.05 30.22 1456 1399 74.72 0.54 tCC(49) in py ring + dHCC(12) in pyr.ring
21 1570 1417 262.44 15.31 1433 1377 21.47 0.28 dHCH(70) CH2 rocking + cC3H18C4H19 (13)
22 1564 1411 163.93 15.37 1419 1364 11.21 0.48 dHCH(18) CH2 rocking
23 1351 1552 1401 15.29 2.29 1403 1348 34.92 9.48 tN12O13(10) + dH18C3C1 (24) + dH18C3N2(31)
24 1519 1371 24.05 8.68 1390 1336 645.33 100 t N12O14(60) + dH18C3N2(11)
25 1330 1500 1354 10.79 2.81 1385 1331 105.20 11.48 dH15C1C3(13) + dH18C3N2(19)
26 1329 1461 1319 218.08 17.27 1379 1325 0.51 4.58 tNC(53) pyr.ring + dH24C8C9(14)
27 1294 1295 1444 1304 3.81 4.06 1333 1281 124.33 6.18 dH18C4C3(32)
28 1425 1286 8.81 0.58 1325 1274 13.96 3.03 dH25C10C9(55)
29 1341 1210 36.15 6.28 1280 1230 15.68 4.07 tCC(31) pyr.ring
30 1184 1308 1180 18.11 3.51 1226 1178 31.42 1.49 d H22O5C1(20) + dH23C7C6(32)
31 1148 1293 1167 98.40 2 1192 1146 59.48 2.35 tC1C3(18) + dH16C1C3C4(19)
32 1285 1160 18.65 53.95 1186 1140 38.06 3.74 tN12C9(15) + dH25C10C9(32)
33 1101 1103 1240 1119 135.76 24.07 1146 1101 83.04 10.11 dH24C8C9(16) + dC3C1O5(25) + dC3C1N2(18)
34 1235 1114 9.73 2.22 1136 1092 21.72 2.07 dH24C8C9(25)
35 1199 1082 84.48 4.02 1085 1042 21.99 2.17 tC3C4(77)
36 1036 1167 1053 2.46 4.04 1082 1040 55.63 1.26 tC1C3(45)
37 1132 1022 0.45 0.59 1026 986 11.29 0.39 dCCC(71) pyr.ring
38 951 1115 1006 2.72 2.62 1003 964 2.53 0.42 s H25C10N11C6(74)
39 1110 1002 16.10 2.23 982 944 0.54 2.04 tCC(23) in.pyr.ing + dH18C1C3C4(19) + cCCNH(73)
40 922 1060 956 0.59 2.89 981 942 3.01 1.53 sHCNC(78) + cCCNH(73)
41 883 1000 903 4.06 3.82 931 894 2.64 2.27 cC3C1O5H22(29) + dH18C1C3C4(23)
42 858 966 872 29.78 13.61 889 854 8.22 1.97 tC1C3(39) + dHCCC(16) pyr.ring
43 960 867 0.85 6.47 872 838 8.16 13.42 tCC(19) pyr.ring + dN12O13O14(18)
44 935 844 24.98 2.23 846 813 15.95 2.38 sH23C7C6N2(70)
45 761 896 809 17.25 8.09 826 793 20.35 0.14 dN12O13O14(13) + dC3N2C6(22) + dC8C9C10(18) pyr. ring
46 872 787 70.65 4.35 774 744 25.13 0.91 dC10N11C6C7(75) pyr. ring
47 834 753 2.47 0.8 736 707 4.08 0.94 dC6N11C10C9(80) pyr .ring
48 697 748 675 23.80 2.13 691 664 14.04 1.29 dN12O13O14(34) + dC8C9C10(11) pyr. ring
49 622 637 696 628 3.15 5.29 647 621 5.53 2.5 dC7C8C9(59) pyr.ring
50 630 568 96.33 8.02 589 565 92.37 7.48 sH19N2C6N11(58)
51 529 532 590 533 25.55 2.28 546 524 16.70 2.04 dC9N12O13(62)
52 505 508 562 508 1.92 4.83 526 505 1.94 3.01 dC1C3N2(44)
504K.Govindarasu,E.Kavitha/SpectrochimicaActaPartA:MolecularandBiomolecularSpectroscopy127(2014)498–510

8. mixed with other bands and normally occur in the region 1266–
1382 cmÀ1
[39–41]. In our study the C–N stretching vibration
observed at 1329 cmÀ1
in FT-Raman spectrum. This vibration the-
oretically calculated at 1325, 1140 and 439 cmÀ1
in B3LYP method
and 1319, 1160 and 443 cmÀ1
in HF method shows good agree-
ment with experimental findings.
CH2 vibrations
The C–H stretching of the methylene groups are at lower fre-
quencies than those of the aromatic C–H ring stretching. The CH2
antisymmetric stretching vibrations are generally observed in the
region 3000–2900 cmÀ1
, while the CH2 symmetric stretching will
appear between 2900 and 2800 cmÀ1
[42,43]. No bands are ob-
served for the CH2 asymmetric stretching vibrations in FT-IR and
FT-Raman spectrum for our title molecule. We predicted the wave-
numbers at 2973 cmÀ1
in B3LYP method and 2931 cmÀ1
in HF
method are assigned to antisymmetric stretching vibrations as
shown in Table 2. CH2 symmetric stretching vibration observed
at 2801 cmÀ1
in FTIR spectrum. The theoretically computed wave-
numbers at 2876 cmÀ1
in dft method and 2858 cmÀ1
in HF method.
The TED corresponding to symmetric type of vibrations shows a
pure mode of above 90% respectively. In the present assignment
the CH2 bending modes follow, in decreasing frequency, the gen-
eral order CH2 deformation CH2 wagg CH2 twist CH2 rock.
Since the bending modes involving the hydrogen atom attached
to the central carbon atom falls in the 1450–875 cmÀ1
range, there
is extensive vibrational coupling of these modes with CH2 defor-
mations, particularly with the CH2 twist. Contreras et al. [44] as-
signed at 1438 cmÀ1
(IR) and 1438 cmÀ1
(Raman) and Ramaekers
et al. [45] assigned at 1447 cmÀ1
for the bending vibrations. For
our title molecule, the CH2 bending mode has been observed at
1458 cmÀ1
in IR spectrum. The theoretically predicted wavenum-
bers at 1454 cmÀ1
and 1474 cmÀ1
by DFT and HF methods respec-
tively are assigned CH2 bending vibrations.
In our title molecule the scaled vibrational frequencies com-
puted by B3LYP method at 1448 cmÀ1
and 1469 cmÀ1
by HF meth-
od is assigned to CH2 scissoring modes of CH2 unit. The calculated
TED corresponding to this mode is also as a mixed mode with 72%
of CH2 scissoring mode. The computed wavenumber at 1364 and
1377 cmÀ1
in B3LYP method and 1411 and 1417 cmÀ1
in HF meth-
od were assigned to CH2 rocking vibration for our title molecule.
The calculated TED corresponding to this mode is a mixed mode
with 70% of CH2 rocking mode.
CH3 vibrations
Two asymmetric and one symmetric stretching vibrations of
CH3 group are usually observed in the range 2990–2950 cmÀ1
[46,47]. In the present case of our molecule, the asymmetric
stretching vibrations of CH3 group have been identified at 2997
and 3014 cmÀ1
by B3LYP method 2945 and 2954 cmÀ1
cmÀ1
by
HF method. The asymmetric stretching vibrations of CH3 group
have been identified at 2927 in DFT method 2875 cmÀ1
in HF
method. No symmetric and asymmetric stretching bands observed
in the FTIR and FT-Raman spectrum of methyl group. The in-plane
bending vibration of the CH3 group is identified at 1460 cmÀ1
in
FT-Raman spectrum and 1481 cmÀ1
in FTIR spectrum. The com-
puted wavenumbers at 1456 cmÀ1
in B3LYP method 1482 cmÀ1
in HF method is assigned to in-plane bending of the CH3 group.
NO2 vibrations
The most characteristics bands in the spectra of nitro com-
pounds are due to NO2 stretching vibrations, which are the two
most useful group wave numbers, not only because of their
spectral region but also for their strong intensity [48]. The
asymmetric and symmetric stretching vibrations of NO2 group
generally give rise to bands in the regions 1500–1570 cmÀ1
and
5347554849523.710.3850748813.740.5dC3N2C6C7(51)
5450345465.703.5646744989.551.6dC3N2C6(29)+sH22O5C1C3(21)
5549144317.541.754574393.623.13tC9N12(12)+dC1C3N2(15)+cC1C3N2C6(16)
564694235.321.054314145.401.01dC10N11C6C7(69)
5741537528.205.4539738199.322.73dC3N2C6(13)+sH22O5C1C3(56)
58399360172.553.0637936451.222.33tN12C9(10)+dCCC(38)pyr.ring+sH22O5C1C3(13)
593232923.460.682972852.940.55dCCC(11)pyr.ring+cC4C3N2C6(17)
603022722.587.132782672.414.15dN2C6C7C8(48)
612492852575.033.562592494.171.81dC9N2C13(40)+dC8C9N12(14)+dH15C1C3C4(11)
622542300.190.462342250.120.38dH15C1C3C4(81)
632211990.443.112061980.462.92dC9N2C4(17)+dCCC(19)pyr.ring+dC10C9C12(28)
641341481340.871.411361310.542.59dC9N12O13(11)+dC6N2C3(37)+dC4C3C1O5(16)
6514112810.529.051211178.139.7dC4C3C1O5(55)
66103932.133.0597931.742.15dC4C3C1O5(21)+dC1C3N2C6(26)+dC3N2C6(18)
6783750.995.3582791.186.75dC10C9N12O13(71)+dC1C3N2C6(13)
6852470.7849.1250480.8030.38dC10C9N12O13(13)+dC1C3N2C6(68)
6941371.5228.0936341.2531.11dC4C3C1O5(12)+dC4C3N2C6(60)
m-stretching;d-in-plane-bending;c-out-of-planebending;s-torsion;w-weak;s-strong;vs-verystrong;vw-veryweak;m-medium.
a
IIR-IRIntensity(KmmolÀ1
).
b
IRa-Ramanintensity(Arbunits)(intensitynormalizedto100%).
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510 505

9. 1300–1370 cmÀ1
in nitrobenzene and substituted nitrobenzenes
[49,50], respectively. In our study the weak symmetric stretching
mode observed at 1351 cmÀ1
in FT-Raman spectrum. The calcu-
lated wavenumbers at 1348 and 1336 cmÀ1
in B3LYP method
and 1371 and 1401 cmÀ1
in HF method assigned to symmetric
stretching vibration of NO2 group. The observed wavenumber at
1351 cmÀ1
in FT-Raman spectrum for symmetric stretching mode
is good agreement with the calculated values at 1348 cmÀ1
by
B3LYP method. The asymmetric stretching vibrations observed at
1583 cmÀ1
in FT-Raman spectrum. The predicted wavenumbers
at 1534, 1582 and 1591 cmÀ1
in DFT method and 1590, 1623 and
1670 cmÀ1
HF method assigned to asymmetric stretching vibration
of NO2 group .The in-plane bending modes are calculated at 664,
793 and 838 cmÀ1
by B3LYP method and 675, 809 and 867 cmÀ1
by HF method and this mode is observed at 697 and 761 cmÀ1
in
FT-IR spectrum. The TED corresponding to this vibration suggests
that it is a very weak mode and exactly contributing to 34%.
Pyridine ring vibrations
Vibrations of the pyridine ring are well known and described in
the literature [51,52]. Also the pyridine ring vibrations of 2-amino-
pyridine, 2-aminopicoline [53], 2-amino-6-methylpyridine [54]
4-N,N-dimethylaminopyridine [55], 2-amino-4nitro and 2-amino-
nitro pyridine [56] were analyzed earlier. Therefore, the assign-
ment of the pyridine ring vibrations in title molecule is relatively
uncomplicated because they are observed at very characteristic
wavenumbers. The ring stretching vibration (C–H) bands are
centered usually on 3090–3020 cmÀ1
[55]. The symmetric C–H
stretching vibrations of pyridine ring appear at 3073 cmÀ1
in
FT-Raman spectra. The calculated wavenumbers at 3089 cmÀ1
in
B3LYP method 3073 cmÀ1
in HF method assigned to C–H symmet-
ric stretching vibration of pyridine ring. Also the calculated wave
numbers at 3105 cmÀ1
B3LYP method and 3076 cmÀ1
in HF meth-
od assigned to C–H symmetric stretching vibration of pyridine ring.
The TED corresponding to this vibration suggests that it is a very
strong mode and exactly contributing to 99%. The in-plane bending
vibrations are usually coupled with the pyridine (C–C) stretching
mode appear in the following regions: 944, 1399 and 1419 cmÀ1
in DFT method and 1002, 1450 and 1465 cmÀ1
in HF method. It
is also observed at 1405 cmÀ1
in FTIR spectrum. The in-plane bend-
ing vibrations are observed at 622, 761 cmÀ1
in FTIR spectrum and
637 cmÀ1
in the FT-Raman spectrum. The computed wavenumber
at 198, 285, 621, 793 and 986 cmÀ1
in B3LYP method and 199, 292,
628, 803 and 1022 cmÀ1
in HF method. The calculated value by the
B3LYP method is good agreement with experimental findings.
NBO analysis
In NBO analysis, the input atomic orbital basis set is trans-
formed via natural atomic orbitals and natural hybrid orbitals into
natural bond orbitals. The NBOs obtained in this fashion corre-
spond to the widely used lewis picture, in which two-center bonds
and lone pairs are localized [57]. The Natural Bond Orbitals (NBOs)
calculations were performed using NBO 3.1 program [58] as imple-
mented 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 subsys-
tem. In the NBO analysis, the electronic wave functions are inter-
preted in terms of a set of occupied Lewis and a set of non-Lewis
localized orbitals [59]. Delocalization effects can be identified from
the presence of off diagonal elements of the Fock matrix 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. How-
ever, the strengths of these delocalization interactions, E(2), are
estimated by second order perturbation theory [60] 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.
In this present work the p electron delocalization is maximum
around N11–C6, C7–C8, C9–C10 distributed to pÃ
antibonding of
C9–C10, C9–N11, N12–O4 with a stabilization energy of about
34.57 kJ/mol, 28.64 kJ/mol, 29.63 kJ/mol shown in Table 3. The
most important interaction energy in this molecule is r electron
donating from LP(1) N11 ? rÃ
(C6–C7), rÃ
(C9–C10) resulting a sta-
bilization energy of about 10.59 kJ/mol, 9.83 kJ/mol respectively. In
title molecule, the other most important interaction energy, is elec-
tron donation from rLP(1) N2 to the antibonding acceptor pÃ
(C6–
N11) orbital with the stabilization energy of about 49.75 kJ/mol
and r(C10–H25) ? pÃ
(C6–N11) with the stabilization energy of
about 5.10 kJ/mol. The appreciable high interaction energy were
observed for LP(2) O3 ? rÃ
(N12–O14), rÃ
(C9–N12) with the sta-
bilization energy of about 19.17 kJ/mol, 11.87 kJ/mol respectively
and LP(3) O13 ? pÃ
(N12–O14) with the stabilization energy of
about 160.32 kJ/mol. The interaction energy observed pÃ
donar
and pÃ
acceptor is pÃ
(C6–N11) ? pÃ
(C9–C10), pÃ
(C7–C8) with en-
ergy of about 146.74 kJ/mol, 95.92 kJ/mol respectively and
pÃ
(N12–O14) ? pÃ
(C9–C10) with energy of about 19.70 kJ/mol.
These molecular charge transfer (r ? rÃ
,p ? pÃ
) can induce large
non-linearity of the molecule.
13
C and 1
H NMR spectral analysis
The molecular structure of SN5N2PLA is optimized by using
B3LYP method with 6-31G(d,p) as a basis set. Then, gauge
invariant atomic orbital (GIAO) 1
H and 13
C calculations of
S-2-5N2PYA1PL are calculated and compared with experimental
data, which are shown in Table 4. The 1
H and 13
C NMR spectra
are presented in supplementary materials S2 and S3. The result
shows that the range of 1
H and 13
C NMR chemical shift of the typ-
ical organic molecule is usually 100 ppm [61,62] the accuracy en-
sures reliable interpretation of spectroscopic parameters. In the
present work, 13
C NMR chemical shifts in the ring for the title com-
pound are 100 ppm, as they would be expected (Table 4). The
oxygen and nitrogen atoms polarize the electron distribution in
its bond to carbon and decrease the electron density at the ring
carbon. Therefore, the chemical shifts values of C9 bonded with
the nitrogen atom shows too high which is observed at
131.64 ppm (C–N) and calculated 129.46 ppm in methanol solu-
tion. Two oxygen atoms of the nitro group have similar negative
charges that are compensated through the positive charges on
the nitrogen and C9 atoms. The nitrogen of the nitro group and
C9 carbon of the pyridine ring are bounded via the single C–N
bond. Similarly, other three carbons peaks in the ring are observed
from 64.84 to 134.86 ppm and are calculated from 62.78 to
137.60 ppm. The important aspect is that, hydrogen attached or
nearby electron withdrawing atom or group can decrease the
shielding and move the resonance of attached proton towards to
a higher frequency. By contrast electron donating atom or group
increases the shielding and moves the resonance towards to a low-
er frequency. The chemical shift values of H atoms are measured in
the range 1.26–8.90 ppm and calculated in the range 1.70–
8.93 ppm. In this present study, the chemical shifts obtained at
1.26 and calculated at 1.70 ppm for the hydrogen atom H22 of
Hydroxyl groups are quite low (63 ppm) due to the shielding ef-
fect. Due to the electron withdrawing (NO2) environmental, the
protons H23 and H24 chemical shifts are high which is observed
506 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

10. at 8.09 and 8.90 ppm calculated at 8.19 and 8.93 ppm. In that, we
calculated chemical shifts for H15 and H16 and H18 are and 3.34
and 3.50 and 3.69 ppm also give a good correlation with the
experimental observations of 3.33 and 3.58 and 3.61 ppm,
respectively.
Nonlinear optical (NLO) effects
The NLO activity provide the key functions for frequency shift-
ing, optical modulation, optical switching and optical logic for the
developing technologies in areas such as communication, signal
processing and optical interconnections [63,64]. The first static
hyperpolarizability (bo) and its related properties (b, ao and Da)
have been calculated using HF/6-31G(d,p) level based on finite
field approach. In the presence of an applied electric field, the en-
ergy 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
[65]. 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 tetra-
hedral. 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=6babcFaFbFcþ . . .
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
Table 3
Second order perturbation theory analysis of Fock matrix in NBO basis for (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol.
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(C6–N11) 1.662 pÃ
(C9–C10) 0.374 34.57 0.32 0.094
p(C7–C8) 1.715 pÃ
(C9–N11) 0.474 28.64 0.26 0.081
pÃ
(C9–C10) 0.374 13.64 0.28 0.057
r(C10–H25) 1.979 pÃ
(C6–N11) 0.023 5.10 1.03 0.065
p(N12–O14) 1.986 LP(3) O13 1.460 11.71 0.17 0.077
p(C9–C10) 1.635 pÃ
(N12–O4) 0.649 29.63 0.15 0.065
pÃ
(C7–C8) 0.265 24.79 0.29 0.078
pÃ
(C6–N11) 0.474 11.93 0.26 0.051
LP(1) N11 1.914 rÃ
(C6–C7) 0.035 10.59 0.87 0.087
rÃ
(C9–C10) 0.032 9.83 0.90 0.085
LP(1) N2 1.724 pÃ
(C6–N11) 0.474 49.75 0.26 0.107
LP(2) O3 1.900 rÃ
(N12–O14) 0.057 19.17 0.70 0.105
rÃ
(C9–N12) 0.097 11.87 0.59 0.075
LP(3) O13 1.459 pÃ
(N12–O14) 0.649 160.32 0.14 0.138
LP(2) O14 1.900 rÃ
(N12–O13) 0.057 19.29 0.70 0.105
rÃ
(C9–N12 0.097 11.84 0.59 0.075
pÃ
(C6–N11) 0.474 pÃ
(C9–C10) 0.374 146.74 0.02 0.081
pÃ
(C7–C8) 0.265 95.92 3.03 0.081
pÃ
(C7–C8) 0.265 RYÃ
(3) C7 0.001 1.93 0.68 0.089
RYÃ
(5) C8 0.000 1.86 0.99 0.105
pÃ
(C9–C10) 0.374 RYÃ
(5) C10 0.001 2.53 0.66 0.084
pÃ
(N12–O14) 0.649 RYÃ
(3) N12 0.008 3.85 2.12 0.141
RYÃ
(2) O14 0.002 3.46 1.12 0.097
RYÃ
(9) N12 0.000 1.22 1.07 0.057
RYÃ
(2) O13 0.002 1.19 1.12 0.057
pÃ
(N12–O14) 0.649 pÃ
(C9–C10) 0.374 19.70 0.13 0.063
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.
Table 4
The observed (Methanol) and predicted 1
H and 13
C NMR isotropic chemical shifts (with respect to TMS, all values in ppm) for (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol.
Atom position Experimental (Methanol) B3LYP/6-31G(d,p) Atom position Experimental (Methanol) B3LYP/6-31G(d,p)
C1 64.84 62.78 H15 3.33 3.34
C3 – 49.32 H16 3.58 3.50
C6 – 152.98 H18 3.61 3.69
C7 107.81 96.06 H19 – 0.99
C9 131.64 129.46 H21 – 0.76
C10 134.86 137.60 H22 1.26 1.70
– – – H23 8.09 8.19
– – – H24 8.90 8.93
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510 507

11. Where
bx ¼ ðbxxx þ bxyy þ bxzzÞ
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
þ ðbzzz þ bzxx þ bzyyÞ2
Š
1=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 mean polarizability ao and total polarizability Da
of our title molecule are 16.1991 Â 10À24
esu and 10.7571 Â 10À24
esu respectively. The total molecular dipole moment and first order
hyperpolarizability are 2.6738 Debye and 7.3759 Â 10À30
esu,
respectively and are depicted in Table 5. Total dipole moment of ti-
tle molecule is approximately two times greater than that of urea
and first order hyperpolarizability is 20 times greater than that of
urea (l and b of urea are 1.3732 Debye and 0.3728 Â 10À30
esu ob-
tained by HF/6-311G(d,p) method). This result indicates the nonlin-
earity of the title molecule.
Electronic properties
UV–Vis spectral analysis
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 [66–68]; thus TD-DFT method is used with B3LYP
function and 6-31G(d,p) basis set for vertical excitation energy of
electronic spectra. Calculations are performed for vacuum/gas
phase, and methanol environment.
The excitation energies, absorbance and oscillator strengths for
the title molecule at the optimized geometry in the ground state
were obtained in the framework of TD-DFT calculations with the
B3LYP/6-31G(d,p) method. The theoretical and experimental max-
imum absorption wavelengths are compared in Table 6. The ultra-
violet spectrum of the title compound is shown in Fig. 4 was
measured in methanol solution. From the Table 6 TD-DFT/B3LYP
method predicts one intense band in electronic transitions for
the methonal solvent and gas phase at 3.563 eV (347.94 nm) and
3.825 eV (324.12 nm) with the oscillator strength 0.445 a.u. and
0.003 a.u. respectively is in good agreement with the measured
experimental data in methonal at 1.1308 eV (362 nm).
Frontier molecular orbitals
Many organic molecules that contain conjugated p-electrons
are characterized as hyperpolarizabilities and are analyzed by
means of vibrational spectroscopy [69,70]. According to the TD-
DFT calculated electronic absorption spectra, the maximum
absorption wave length corresponding to the electronic transition
is from the HOMO to the LUMO. Energy difference between HOMO
and LUMO orbital is called as energy gap that is an important sta-
bility for structures and it is a critical parameter in determining
molecular electrical transport properties [71,72]. The plots of
HOMO and LUMO are shown in supplementary material S4. This
electronic absorption corresponds to the transition from the
ground state to the first excited state and is mainly described by
one electron excitation from HOMO to LUMO. While the energy
of the HOMO is directly related to the ionization potential, LUMO
energy is directly related to the electron affinity. In addition,
According to B3LYP/6-31G(d,p) calculation, the energy band gap
of the molecule is about 4.2431 eV. The HOMO orbitals are local-
ized mainly on the all group of the molecule. On the other hand,
the LUMO orbitals are localized mainly on (5-Nitro-2-pyridyl)
group and exception of methyl and hydroxyl group.
HOMO energy ¼ À6:3907 eV
LUMO energy ¼ À2:1476 eV
HOMO À LUMO energy gap ¼ 4:2431 eV
Atomic charges
Mulliken atomic charge calculation [73] has an important role
in the application of quantum chemical calculation to molecular
system. The mulliken atomic charges are calculated at B3LYP/6-
31G(d,p) level by determining the electron population of each
atom as defined by the basis function shown in supplementary
material S5. The carbon atoms C6 (0.476) have the highest positive
charge when compared with all other carbon atoms as shown in
Table 5
The electric dipole moment, polarizability and first order hyperpolarizability of (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol 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 0.8966 axx 69.8448 10.3510 bxxx 28.9345 249.9651
ly À1.8606 axy À10.1310 À1.5014 bxxy 18.1449 156.7538
lz À1.6981 ayy 128.2290 19.0035 bxyy À146.2773 À1263.6896
l 2.6738 axz À24.2430 À3.5928 byyy 213.4871 1844.3151
ayz 26.1792 3.8798 bxxz 1.2755 11.0190
azz 129.8425 19.2427 bxyz À126.4022 À1091.9886
ao 109.3054 16.1991 byyz 431.0851 3724.1442
Da 72.5856 10.7571 bxzz À11.0487 À95.4497
byzz 389.9730 3368.9767
bzzz 138.6719 1197.9865
btot 853.7888 7375.8814
Table 6
The experimental and computed absorption wavelength k (nm), excitation energies E
(eV), absorbance and oscillator strengths (f) of (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol
in methanol solution and gas phase.
Experimental TD-DFT/B3LYP/6-31G(d,p)
Methanol Methanol Gas
k (nm) E (eV) k (nm) E (eV) f (a.u.) k (nm) E (eV) f (a.u.)
362 1.1308 347.94 3.563 0.445 324.12 3.825 0.003
– – 309.69 4.004 0.001 310.31 3.9955 0.386
– – 297.57 4.167 0.000 297.10 4.1731 0.001
508 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510

12. the histogram supplementary material S6. Due to the reason this
carbon atom is bonded to N atom of the donor NH group. More-
over, hydrogen atoms connected to oxygen atom have the maxi-
mum positive charges H22 (0.315), at the DFT calculation this is
due to the reason of electro negative Oxygen of the OH group.
The NH group of Nitrogen atom N2 (À0.558) have the bigger neg-
ative charges compare to all other Nitrogen atoms in the molecule.
Nitrogen atom of the nitro group has large positive charge value
N12 (0.366). This is due to the presence of electronegative oxygen
atom in the nitro group. The OH group Oxygen atom have the high-
est negative charge O5 (À0.537) compare other Oxygen atoms O13
(À0.408) and O14 (À0.409) in the nitro group of the title molecule.
Molecular electrostatic potential (MEP)
MEP is related to the electronic density and is a very useful
descriptor in understanding sites for electrophilic and nucleophilic
reactions as well as hydrogen bonding interactions [74]. 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 as well as hydrogen
bonding interaction [75,76]. MEP values were calculated using
following the equation [77]:
VðrÞ ¼
X
ZA=jRA À rj À
Z
qðr0
Þ=jr0
À rjd3r0
where ZA is the charge of nucleus A located at RA, q(r’) is the elec-
tronic density function of the molecule, and r’ is the dummy inte-
gration variable. To predict reactive sites for electrophilic and
nucleophilic attack for the title molecule, MEP was calculated at
the B3LYP/6-31G(d,p) optimized geometry as shown in supplemen-
tary material S7. The different values of the electrostatic potential
represented by different colors; red represents the regions of the
most negative electrostatic potential, white represents the regions
of the most positive electrostatic potential and blue represents
the region of zero potential. The color code of these maps is in
the range between À0.0500 (deepest red) and +0.0500 (white) in
the title compound, where white indicates the strongest attraction
and red indicates the strongest repulsion. According to these calcu-
lated results, 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. The negative (red color) regions of
MEP were related to electrophilic reactivity and the positive (white
color) ones to nucleophilic reactivity.
Global reactivity descriptors
By using HOMO and LUMO energy values for a molecule, the
global chemical reactivity descriptors of molecules such as
hardness (g), chemical potential (l), softness (S), electronegativity
(v) and electrophilicity index (x) have been defined [78,79]. 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
The chemical potential of the molecule is
g ¼ ÀðI þ AÞ=2
The softness of the molecule is
S ¼ 1=2g
The electronegativity 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
potetional A and an electron affinity I of our molecule SN5N2PLA
calculated by B3LYP/6-31G(d,p) method is 2.1476 and 6.3907
respectively. The calculated values of the Hardness, Softness,
Chemical potential, Electronegativity and Electrophilicity index of
our molecule is 2.1216, 4.2432, À4.2692, 4.2692 and 4.2954
respectively as shown in supplementary material S8. Considering
the chemical hardness, large HOMO–LUMO gap represent a hard
molecule and small HOMO–LUMO gap represent a soft molecule.
Thermodynamic properties
Based on the vibrational analysis of our title molecule at
B3LYP6-31G(d,p) basis set, the thermodynamic parameters such
as Heat capacity (C0
p,m), entropy (S0
m) and enthalpy (H0
m) were
calculated using perl script THERMO.PL [80] and are listed in Supple-
mentary material S9. From the Supplementary material S9 it can be
seen that, when the temperature increases from 100 to 1000 K the
thermodynamic functions (C0
p,m, S0
m, H0
m) are also increases, because
molecular vibrational intensities increase with temperature [81].
Fitting factor (R2
) of the thermodynamic functions such as heat
capacity, entropy and enthalpy changes are 0.978, 0.967 and 0.976
respectively. The correlation graphics of temperature dependence
of thermodynamic functions for SN5N2PLA molecule are shown in
Supplementary material S10. Vibrational zero-point energy of the
SN5N2PLA is 521.43 kJ/mol.
Conclusion
The FT-IR, FT-Raman spectra, 1
H, 13
C NMR and UV–Visible spec-
tra of (S)-(À)-N-(5-Nitro-2-pyridyl) alaninol have been recorded
and analyzed. The optimized molecular structures, vibrational
frequencies and corresponding vibrational assignments of title
molecule have been calculated using HF and B3LYP method with
6-31G(d,p) as basis set. Comparison of the experimental and calcu-
lated 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 funda-
mentals is very small. The UV spectrum was measured in methanol
solution and results are compared with theoretical results. The
NBO analysis revealed that the LP(3) O13 ? pÃ
(N12–O14) interac-
tion gives the strongest stabilization to the system around at
160.32 kJ/mol. The lowering of the HOMO ? LUMO energy gap
Fig. 4. The UV–Visible spectrum (Methanol) of (S)-(À)-N-(5-Nitro-2-pyridyl)
alaninol.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 498–510 509

13. explains the charge transfer interaction takes place within the mol-
ecule. The 1
Hand 13
C NMR magnetic isotropic chemical shifts were
calculated by B3LYP/6-31G(d,p) basis set and compared with
experimental findings. The MEP map shows that the negative po-
tential sites are on oxygen atoms as well as the positive potential
sites are around the hydrogen atoms. The greater dipole moment
and hyperpolarizability of the title molecule shows the large NLO
optical property of the title molecule. The chemical hardness,
chemical softness and electrophilicity index of the SN5N2PLA mol-
ecule are calculated. The thermodynamic properties (heatcapacity,
entropy and enthalphy) in the temperature range from 100 to
1000 K also 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 data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.02.107.
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