Synthesis and spectroscopical study of rhodanine derivative using DFT approaches

Article abstract of DOI:10.1016/j.saa.2015.02.097

Abstract The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of (E)-5-benzylidene-2-thioxothiazolidine-4-one (E5BTTO) have been investigated experimentally and theoretically based on Density Functional Theory

Full text of DOI:10.1016/j.saa.2015.02.097

Accepted Manuscript
Synthesis and spectroscopical study of rhodanine derivative using DFT ap-
proaches
R. Anbarasan, A. Dhandapani, S. Manivarman, S. Subashchandrabose, H.
Saleem
PII:
S1386-1425(15)00271-1
http://dx.doi.org/10.1016/j.saa.2015.02.097
SAA 13399
DOI:
Reference:
To appear in:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
Received Date:
Revised Date:
Accepted Date:
6 November 2014
28 January 2015
19 February 2015
Please cite this article as: R. Anbarasan, A. Dhandapani, S. Manivarman, S. Subashchandrabose, H. Saleem,
Synthesis and spectroscopical study of rhodanine derivative using DFT approaches, Spectrochimica Acta Part A:
Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.02.097
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Synthesis and spectroscopical study of
Rhodanine derivative using DFT approaches
a
a
a
b
c
R. Anbarasan , A. Dhandapani , S. Manivarman * S. Subashchandrabose , H.Saleem
a
Post Graduate and Research department of chemistry, Government Arts College, C-Mutlur,
Chidambaram-608102, Tamil Nadu, India.
b
Centre for Research & Development, PRIST University, Vallam, Thanjavur-613403, Tamil
Nadu, India.
c
Department of Physics, Annamalai University, Annamalai nagar-608002, Chidambaram, Tamil
Nadu, India.
Abstract
The optimized molecular structure, vibrational frequencies, corresponding vibrational
assignments of (E)-5-Benzylidine-2-thioxothiazolidine-4-one (E5BTTO) have been investigated
experimentally and theoretically based on Density Functional Theory (DFT) approach. The FT-
Raman and FT-IR spectra of E5BTTO were recorded in solid phase. Theoretical calculations
were performed at the DFT level using the gaussian03 program. The experimental bands were
assigned and characterized on the basis of the scaled theoretical wavenumber by their Total
Energy Distribution (TED). The results of the calculation were applied to simulate infrared and
raman spectra of the title compound which showed good agreement with the observed spectra.
The calculated HOMO and LUMO energies show that charge transfer occur within the molecule.
Stability arising from Hyperconjugative interactions leading to its NLO activity and charge
delocalization were analyzed using Natural Bond Orbital (NBO) analysis.
Keywords: Rhodanine; TED; NLO; NBO; HOMO-LUMO;
*Corresponding author
E-mail : drsmgac@gmail.com (Dr. S. Manivarman).
:
sscbphysics@gmail.com (Dr. S. Subashchandrabose)
Mobile : +91 9842483139.
1

1
. INTRODUCTION
Rhodanine is a five-membered heterocyclic ring with diverse applications particularly in
biochemistry, medicinal chemistry, photochemistry, industry and coordination chemistry [1].
Rhodanine represents a privileged scaffold in drug discovery [2] and its derivatives, which are
common reagents in analytical and coordination chemistry, attract special interest in medicine,
biochemistry, and photochemistry. Rhodanine derivatives modified at the methylene group
(
ylidenerhodanines) possess antibacterial [3], antifungal [4-6], antidiabetic [7], and anticancer
activity [8]. This accounts for the use of rhodanine in the pharmaceutical industry. Chemical
properties of rhodanine and its derivatives are of interest due to coordination capacity and their
use as metal extracting agents and as analytical reagents [9, 10]. Azo compounds based on
rhodanine were synthesized as potential medical preparations [11–14]. The rhodanine moiety has
been synthesized by various methods such as addition of isothiocyanate to mercaptoacetic acid
followed by acid catalyzed cyclisation, or the reaction of ammonia or primary amines with
carbon disulfide and chloroacetic acid in the presence of bases [15, 16].
Recently, substituted rhodanines were investigated for tau aggregation inhibitor
properties [17]. Rhodanines are classified as non-mutagenic [18] and a long-term study on the
clinical effects of the rhodanine-based Epalrestat as an anti-diabetic, demonstrated that it is well
tolerated [19]. Additionally, rhodanines have been designed as inhibitors of various enzymes
such as bacterial β-lactamase and Mur ligases. Rhodanine derivatives were found to have marked
mildew-proofing activity [20]. Arylidenerhodanines are frequently identified as potent hits in
high throughput screening against various prokaryotic and eukaryotic targets. Photo physical
studies for complex molecules having both a donor and an acceptor moiety separated by a π-
bridge are very important in optical spectroscopy and the study of intramolecular charge transfer
(
ICT) processes [21–23]. Recent studies have shown that this type of molecular framework is
interesting for its potential in the design and synthesis of non-linear optical (NLO) materials [24,
5], due to their asymmetric charge distribution and large molecular hyperpolarizabilities. The
2
optical absorption properties of azo dye rhodanine derivatives thin films have been studied by El-
Ghamaz et al. [26]. Authors identified the values of the energy band gap, Eg for derivatives were
in the range1.77–2.29 eV depending on the nature of the substituent. Therefore, the synthesis of
these rhodanine derivatives shows considerable interest in optical studies.
The literature survey reveals that no attempt has been made so far to investigate the
vibrational spectra and theoretical calculations for (E)-5-benzylidene-2-thioxothiazolidin-4-one.
Hence, we set out to explore the vibrational and Non-linear optical behaviors of (E)-5-
benzylidene-2-thioxothiazolidin-4-one theoretically based on Density Functional Theory
calculations. The aim of this work is to carry out an experimental and theoretical study on this
compound with quantum chemical methods in order to better understand its structural and
vibrational properties. The obtained parameters may be used to gain chemical and vibrational
2

insights into related compounds. Moreover, density functional theory (DFT), natural bond orbital
NBO) and thermodynamic property calculations were performed to analyze the energies and
(
geometrical parameters of (E)-5-benzylidene-2-thioxothiazolidin-4-one in the gas phase as well
as the magnitude of intramolecular interactions.
2
2
. Experimental
.1 Synthesis of (E)-5-benzylidene-2-thioxothiazolidin-4-one:
An efficient synthesis of (E)-5-Benzylidine-2-thioxothiazolidine-4-one by the
condensation of benzaldehyde with 2-thioxo thiazolidine-4-one in sodium acetate/acetic acid
under ethanol medium at 90°C for 3 hours. After the completion of the reaction was monitored
by TLC, the obtained yellow crystals are separated and dried. The crude product was purified by
recrystallized with absolute ethanol. The observed melting point of the compound is 202 °C (lit.
melting point 198-202 °C) [27]. The yield of the product was about 80%. The schematic diagram
of synthesis is shown in Figure.1.
2
.2. FT-IR and FT-Raman spectra
−
1
The FT-IR spectrum of the synthesized rhodanine was measured in the 4000–400 cm
region at the spectral resolution of 4 cm
−
1
using on SHIMADZU FT-IR affinity
Spectrophotometer (KBr pellet technique) made in Japan. The FT-IR spectrum was recorded in
Faculty of Marine Biology, Annamalai University and only noteworthy absorption levels are
listed. The FT-Raman spectrum of the title compound was recorded on BRUKER: RFS27
−
1
spectrometer operating at laser 100mW in the spectral range of 4000–50 cm . FT-Raman
spectral measurements were carried out from Sophisticated Analytical Instrument Facility
(
SAIF), Indian Institute of Technology (IIT), Chennai.
. Computational details
The quantum chemical calculations of E5BTTO have been performed using the B3LYP
3
level of theory supplemented with the standard 6-311++G(d,p) basis set, using the Gaussian 03
program. The entire calculations were performed at DFT levels on a Pentium IV/3.02 GHz
personal computer using Gaussian 03W [28] program package, invoking gradient geometry
optimization [28, 29]. Initial geometry generated from standard geometrical parameters was
minimized without any constraint in the potential energy surface at DFT level, adopting the
standard 6-311++G(d,p) basis set. The optimized structural parameters were used in the
vibrational frequency calculations at the DFT level to characterize all stationary points as
minima. Then, vibrationaly averaged nuclear positions of E5BTTO were used for harmonic
vibrational frequency calculations resulting in IR and Raman frequencies together with
intensities and Raman depolarization ratios. In this study, the DFT method (B3LYP/6-
3
11++G(d,p)) was used for the computation of molecular structure, vibrational frequencies and
energies of optimized structures. The vibrational modes were assigned on the basis of TED
3

analysis using VEDA4 program [30]. It should be noted that the Gaussian 03W package able to
calculate the Raman activity. The Raman activities were transformed into Raman intensities
using Raint program [31] by the expression:
1
ν i
−
12
4
I i = 10
× (ν − ν ) ×
× R Ai
(1)
0
i
Where I
i
is the Raman intensity, Ai is the Raman scattering activities, ν
i
is the
wavenumber of the normal modes and ν
0
denotes the wavenumber of the excitation laser [32].
For meeting the requirements of both accuracy and computing economy, theoretical methods and
basis sets should be considered. Density functional theory (DFT) has been proved to be
extremely useful in treating electronic structure of molecules. The basis set 6-311++G(d,p) was
used as an effective and economical level to study. After the most stable conformer of the title
compound determined, geometry optimizations of this conformer have been performed by
B3LYP method.
4
. RESULTS AND DISCUSSION
4
.1 Molecular Geometry
(
E)-5-benzylidene-2-thioxothiazolidin-4-one (E5BTTO) is subjected to geometry
optimization in the ground state. The optimized structure belongs to C point group symmetry.
1
The optimized molecular structure of E5BTTO is shown in Figure 2, with numbering scheme
adopted in this study. The calculated geometrical parameters of E5BTTO calculated by B3LYP
with 6-311++G(d,p) basis set are listed in Table 1. To the best of our knowledge there is no exact
crystal data is available for this compound. Therefore, we compare the bond length and angles
with related molecule. Baryshnikov et al., [33] reported the bond lengths of C−C and C−S for
simple rhodanine molecule is 1.525 and 1.836 Å, respectively. In our present study, the
corresponding bond lengths of C
1
−C
2
and C
2
−S are calculated as 1.4846 and 1.7923 Å, these
6
values are lesser than the rhodanine molecule due to the attachment of benzaldehyde carbon
atom. These bonds are contracted due to wander waals contraction. The bond distance of C=S,
C=O and N−H of E5BTTO is 1.7923, 1.2144 and 1.0127 Å, respectively. These bond distances
are in good agreement with the 1.771, 1.213 and 1.016 Å bond distances of rhodanine ring [33].
On the other hand, the C−C bond length (C10−C12, C12−C15, C15−C17, C17−C13, C13−C11 and
C
11−C10) of six membered rings are relatively equal to 1.39 Å/B3LYP with some exceptions.
Because in benzene, all the C-C bond lengths are equal (equal distribution of π-electrons around
the benzene ring). The bond angles of S −C −N , C −N −C , N −C −C , C −C −S , C −S −C
−C −S , S −C −N and N −C −O are 108.2, 120.46, 109.0, 108.9, 93.2, 125.4, 126.2 and
21.8°, respectively. These bond angles are relatively equal to simple rhodanine molecule. The
6
3
4
3
4
1
4
1
2
1
2
6
2
6
3
,
S
6
3
7
7
3
4
4
1
8
1
bond length, bond angles of E5BTTO were listed in Table S1.
4

4
.2 Vibrational assignments
The aim of the vibrational analysis is to find vibrational modes connected with specific
molecular structures of calculated compound. The title molecule consists of 21 atoms, which
undergo 57 normal modes of vibrations. It is in agreement with C point group symmetry, major
1
vibrations are active in both Raman and infrared absorption. The detailed vibrational assignment
of the experimental wavenumber based on normal mode analyses and a comparison with
theoretically scaled wavenumber with TED using VEDA4 program [30]. The calculated
frequencies are usually higher than the corresponding experimental quantities, due to the
combination of electron correlation effects and basis set deficiencies. These discrepancies
overcome by applying the appropriate scaling factors; the theoretical calculations reproduce the
experimental data well in agreement. Calculated Raman activities and IR intensities help us to
distinguish and more precisely assign those fundamentals, which are close in frequency. The
simulated and spectra of FT-IR and FT-Raman spectra are shown in Figures 3 and 4,
respectively. The experimental and scaled theoretical harmonic vibrational frequencies along
with the calculated Total Energy distribution values were given in Table 1. We know that ab
initio HF and DFT potentials systematically overestimate the vibrational wavenumber. These
discrepancies are corrected either by computing anharmonic corrections explicitly or by
introducing a scaled field or by directly scaling the calculated wavenumber with a proper factor
[
34].
.2.1 N−H vibration
The vibrations belonging to N−H stretching always occur in the region 3450–3250 cm
4
−
1
which is the characteristic region for ready identification of this structure [35, 36]. In this region,
the bands are not affected appreciably by the nature of the substituents. In the present work, the
−
1
scaled N−H stretching vibration is calculated at B3LYP/6-311++G(d,p) at 3450 cm and the
−
1
corresponding stretching vibration is observed as a medium band in FT-IR at 3431 cm (mode
no.1). The stretching vibration of N−H is identified as pure mode with 100% TED values. Sert et
−
1
al., have observed these modes at 3465 and 3450 cm for 6-(2-methylpropyl)-4-oxo-2-
sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carbonitrile [37]. For the meantime, Srivastava et
−
1
al., have calculated the N−H stretching vibrations at 3458 and 3456 cm at B3LYP for 2-(2,4-
dichlorophenyl)-N-(1,3-thiazol-2-yl)acetamide [38]. Conversely, no Raman band is observed for
the N−H stretching modes in the experimental spectra.
−
1
The N−H in-plane bending vibrations are observed at 1393 and 1137 cm from B3LYP
mode nos. 14 and 22). All of these modes are strongly coupled with the other in plane, out of
(
plane bending and torsional vibrations. Therefore, the bending vibrations of N−H were shifted to
−
1
lower wavenumber. The torsional vibration of H−N−C−C were observed at 505 cm at
theoretical wavenumber and its corresponding TED value is 92%. Tamer et al., reported the out
−
1
of plane H−N−C−C at 607 and 532 cm for B3LYP level [39].
5

4
.2.2 C=O vibration
Stretching vibration of C=O group is expected to appear at 1715–1680 cm [40].
−
1
Carbonyl absorptions are very sensitive and both the carbon and the oxygen atoms move during
the vibration having nearly equal amplitude. Carbonyl group vibrations give rise to characteristic
bands in vibrational spectra and for this reason, such bands have been subject of extensive
studies [41]. Any deviation of the calculated wavenumber for this mode can be attributed to π-
electron delocalization due to the conjugation or formation of hydrogen bonds [42]. In the
−
1
present case the C
1
=O
8
−
stretching band is observed as very strong band at 1697 cm in FT-IR
1
spectrum and 1680 cm as medium band in FT-Raman spectrum are observed for corresponding
−
1
mode. The theoretical wavenumber at 1680 cm shows very good agreement with experimental
value and TED corresponding to this vibration suggests that it is a pure mode and exactly
contributing to 82%. The in-plane bending and out-of-plane bending vibrations of CO is
−
calculated at 714, 497, 416 and 358 cm 1 (mode no’s: 36, 44, 46 and 48) correlates well with
−
1
−1
band observed at 708 and 434 cm in FT-Raman and 428 cm in FT-IR spectrum.
4
.2.3 C=S and C-S vibrations
In general, the assignment of band due to the C–S stretching vibration in different
compounds is difficult in the infrared, since the band is of variable intensity and may be found
−
1
over the wide region 1035–245 cm , whereas, C–S stretching vibration results in strong bands in
Raman spectra which are normally easy to identify [43]. Xavier et al., reported that the C–S
group is less polar than carbonyl links and has a considerably weaker band. In consequence, the
band is not intense, and it falls at lower frequencies, where it is much more susceptible to
coupling effects and identification is therefore difficult and uncertain [44]. In this study, the
−
1
C
3
=S stretching vibration is observed as medium band at 1029 cm in FT-Raman spectrum and
7
−
1
the theoretical wavenumber observed at 1030 cm well matches with the experimental
one(mode no: 24). Its TED contribution is about 42%. Besides the stretching vibrations, the
sulfur atom gives rise to bending vibrations with neighboring atoms.
The C
2
-S
6
vibrations were observed with coupled vibrations of neighboring atoms. The
−
1
strong C-S stretching vibrations are observed at 949 and 648 cm in B3LYP and these vibration
modes are coincide with FT-IR band at 634 cm (mode no’s: 33 and 38). The phenyl ring
deformation vibration is observed very strongly at 810 cm in FT-IR spectrum and its
corresponding theoretical wavenumber assigned at 808 cm from B3LYP. The rhodanine
−
1
−
1
−
1
−
1
−1
breathing mode is strongly observed at 524 cm in FT-IR and as medium band at 521 cm in
−
1
FT-Raman, the theoretical wavenumber well coincides at 524 cm from B3LYP. The C−S
vibrations accompanied with phenyl ring deformation and breathing mode vibrations of
rhodanine. The in-plane bending and out-of-plane bending vibrations of C−S group were also
found well within the characteristic region [45, 46].
6

4
.2.4 C−N vibration
The identification of C–N and C=N vibrations are a very difficult task, since the mixing
of several modes are possible in the region. The C−N stretching vibration coupled with
−
1
scissoring of N−H, is moderately to strongly active in the region 1300 cm [47]. Saima jabeen
at al., [48] reported the C−N stretching vibrations of rhodanine molecule at 1234, 1187 and 820
cm in FT-IR spectrum and bands at 1230, 1176 and 878 cm in FT-Raman. Ramalingam et al.,
−
1
−1
−
1
−1
[
49] reported the C−N stretching vibration at 1316cm and 1213cm for morpholine-4-
ylmethylthiourea. In accordance with the above conclusion, the C−N stretching vibrations are
−
1
observed at 1393 and 1230 cm from theoretical wavenumber, which shows good agreement
−
1
with the strong vibrational band observed at 1236 cm in FT-IR spectrum. The counterpart
−
1
vibration in FT-Raman observed as medium band at 1222cm (mode no: 18).
Subashchandrabose at al., [50] assigned the C−N out-of-plane bending vibration at 664
−
1
−1
cm (FT-IR)/666 cm (FT-Raman). The in-plane and out-of plane-bending vibrations of C−N
−
1
bonds are observed at 988, 743, 674, 619, 529 and 373 cm in B3LYP. The band observed at
−
1
−1
6
34 cm in FT-IR spectrum and band observed at 708 cm in FT-Raman spectrum shows good
agreement with the theoretical wavenumber. The TED of C−N bending vibrations lies in the
range 10-92%.
4
.2.5 C-H vibrations
In aromatic molecules, the C−H stretching vibrations appear in the range of 3100–3000
−
1
cm [51]. The phenyl C−H stretching modes are typically exhibited as multiplicity of weak to
moderate bands compared with the aliphatic C−H stretching [52]. The aromatic C−H stretching
vibration shows a signal at 3061 cm in FT-IR and bands observed at 3065 and 3015 cm in
FT-Raman also corresponds to the same vibration mode. The harmonic wavenumber corresponds
to aromatic C−H vibrations calculated at 3110, 3067, 3057, 3045, 3037 and 2997 cm (mode
no’s: 2-7). Moreover, its total energy distribution value shows greater than 90%. As it is evident
from Table 1, these vibrations are almost pure modes. It is well known that the aliphatic C−H
stretching vibrations are observed at lower wavenumber than the ring C−H stretching vibrations.
−
1
−1
−
1
−
1
The C
9
−H21 stretching vibration was observed at 2997 cm and is lesser than the aromatic C−H
stretching vibrations.
The C−H in plane bending ring vibrations normally are shown as a number of strong to
−
1
weak sharp bands in the region 1300–1000 cm [53, 54]. The C−H in-plane bending vibrations
−
1
of the title compound are identified at 1309, 1160, 1067 and 998 cm in FT-Raman spectrum
−
1
and 1068 cm in FT-IR spectrum, respectively. The theoretically calculated frequencies for the
−
1
C−H in-plane bending vibration are calculated at 1368, 1314, 1171, 1141, 1137 and 1072 cm
mode no’s: 15, 16, 20, 21, 22 and 23). The theoretically calculated wavenumber shows good
agreement with the experimental values. The C−H out-of-plane bending vibrations are strongly
(
−
1
coupled vibrations and normally observed in the region 950-809 cm [55, 56]. In the present
−
1
study, the C−H out-of-plane bending bands are observed at 914 and 765 cm /FT-IR and 851
7

−
1
cm /FT-Raman. The theoretically calculated wavenumber are at 960, 921, 879, 827 and 747
−
1
cm (mode no’s: 28, 30, 31, 32 and 34) shows well agreement with the experimental values.
.2.6 Ring vibrations
The ring stretching vibrations are very much important in the IR spectrum of benzene
4
derivatives because they are highly characteristic modes of the aromatic rings. Many ring
vibrations are affected by the substitution to the aromatic ring of benzene derivatives. The six
ring carbon atoms undergo coupled vibrations, called skeletal vibration. The ring C=C and C−C
stretching vibrations, known as semicircle stretching usually occurs in the region 1400–1625
−
1
cm . The actual positions of these modes are determined not so much by the nature of the
substituents but by the form of substitution around the ring [57, 58]. Zhang et al., reported the
−
1
aromatic C=C stretching vibrations at 1488, 1436 and 1409 cm for HBAH [59]. Balachandran
−
1
et al., reported the FT-IR bands identified at 1595, 1583, 1571, 1476, 1452, 1418 and 1368 cm
−
1
and the FT-Raman bands at 1569, 1472, 1438, 1411 and 1356 cm are assigned to C=C
stretching vibrations of NpMBA. Based on the above literature, the C=C stretching vibration for
the title compound is observed at 1589, 1435, 1296, 1190 and 1014 cm in FT-IR spectrum and
bands at 1592, 1570, 1441 and 1182 cm in FT-Raman spectrum. These experimental bands
shows good correlation with the bands observed at 1579, 1557, 1535, 1424, 1282, 1189 and 1013
−
1
−
1
−
1
cm from theoretically calculated wavenumber.
−
1
In our present study, the band observed at 976 and 1013 cm in B3LYP theoretical
wavenumber is assigned to trigonal bending and breathing mode of the phenyl ring and it shows
−
1
good agreement with experimental FT-IR medium band at 1014 cm (mode no: 25). It is evident
from Table 1, in our present study the C−C−C in-plane bending vibrations are observed at 976,
−
1
−1
7
40, 609 and 577 cm . The out-of-plane bending vibrations are observed at 486 and 106 cm in
theoretically calculated wavenumber. The torsional modes of C−C−C−C in theoretical
−
1
wavenumber is observed at 674, 486, 404 and 358 cm . The vibration observed very strongly at
−
1
−1
6
75 cm /FT-IR and 673 cm /FT-Raman shows good agreement with calculated torsional
modes. The rest of the observed, calculated wavenumber and the corresponding assignment of
the title molecule are shown in Table 1.
4
.3 Non-Linear Optics
The first hyperpolarizabilities (β
0
, α and ∆α) of (E)-5-benzylidene-2-thioxothiazolidin-4-
0
one is calculated using B3LYP/6-311++G(d,p) basis set, based on the finite-field approach. In
the presence of an applied electric field, the energy of a system is a function of the electric field.
First hyperpolarizability is a third rank tensor that can be described by a 3x3x3 matrix. The 27
components of the 3D matrix can be reduced to 10 components due to Kleinman symmetry [60].
It can be given in the lower tetrahedral format. It is obvious that the lower part of the 3x3x3
matrix is a tetrahedral. The components of β are defined as the coefficients in the Taylor series
8

expansion of the energy in the external electric field. When the external electric field is weak and
homogeneous, this expansion becomes:
0
E = E − µ F −1/ 2α F F −1/ 6β F F F
(2)
α
α
αβ
α
β
αβγ
α
β
γ
0
Where E is the energy of the unperturbed molecules, F
α
is the field at the origin, and
µ ,α , β
are the components of the dipole moment, polarizability and the first
α
αβ
αβγ
hyperpolarizabilities, respectively. The total static dipole moment µ, the mean polarizability α
0
,
the anisotropy of polarizability ∆α and the mean first hyperpolarizability β , using the x, y, z
0
components are defined as [61]
2
x
2
y
2 1/2
z
µ =(µ +µ +µ )
(3)
(4)
α +α +α
zz
xx
yy
α =
0
3
1
/ 2
2
2
2
−
1 / 2

2
xy
2
yz
2
xz


(5)
(6)
∆
α = 2
(
α xx − α yy
)
+
(
α yy − α zz
)
+
(
α zz − α xx
)
+ 6
(
α
+ α + α
)


1
2
)
/ 2
2
β x + β y + β z
2
β 0
=
(
Many organic molecules, containing conjugated π electrons are characterized by large
values of molecular first hyperpolarizabilities, were analyzed by means of vibrational
spectroscopy [62-65]. The intra molecular charge transfer from the donor to acceptor group
through a single-double bond conjugated path can induce large variations of both the
molecular dipole moment and the molecular polarizability, making IR and Raman activity
strong at the same time [66].
Theoretical investigation plays an important role in understanding the structure–property
relationship, which is able to assist in designing novel NLO materials. It is well known that the
higher values of dipole moment, molecular polarizability, and hyperpolarizability are important
for more active NLO properties. The present study reveals that the π-π interaction can make
larger intramolecular interaction and hence the polarizability of the molecule increases. It is
evident from Table S2, the molecular dipole moment (µ), molecular polarizability and
-30
hyperpolarizability are calculated about 1.6470 (D), 0.507 and 4.414 x10 esu, respectively. The
β
0
value of the title compound is twelve times greater than that of urea.
.4 Natural bond orbital analysis
NBO analysis provides an efficient method for studying intra and intermolecular
4
bonding and interaction among bonds and also provides a convenient basis for investigation
charge transfer or conjugative interactions in molecular system. Another useful aspect of NBO
9

method is that it gives information about interactions in both filled and virtual orbital spaces that
could enhance the analysis of intra and intermolecular interactions. The hyperconjugation may
be given as stabilizing effect that arises from an overlap between an occupied orbital with
another neighboring electron deficient orbital when these orbitals are properly orientation. This
non-covalent bonding–antibonding interaction can be quantitatively described in terms of the
NBO analysis, which is expressed by means of the second-order perturbation interaction energy
(2)
(
E ) [67–70]. This energy represents the estimation of the off-diagonal NBO Fock matrix
elements. It can be deduced from the second-order perturbation approach [71]
2
F (i, j )
ε − ε
(
2 )
E
= ∆ E ij = qi
(6)
j
i
Where, qi is the donor orbital occupancy, εi and εj are diagonal elements (orbital
energies) and F(i, j) is off diagonal NBO Fock matrix elements.
NBO analysis was performed by the B3LYP level of theory with 6-311++G(d,p) basis set
for the molecule E5BTTO and are listed in Table 2. NBO theory allows the assignment of
hybridization of atomic lone pairs and of the atoms involved in bond orbitals. These are important
data in spectral interpretation as the frequency ordering is related to the bond hybrid composition.
Transitions between non-bonding atomic orbitals holding unshared pair of electrons from sulfur
and nitrogen to anti-bonding π orbitals shows strong delocalization occurring within the rhodanine
ring. The hyperconjugative interaction energies from non-bonding N
4
and S
6
to anti-bonding
orbitals C −O , C −S and C −C , C −S shows the energies of 208.03, 280.83 and 66.90, 159.49
1
8
3
7
2
9
3
7
kJ/mole, respectively, shows the charge delocalization of the rhodanine ring. The electron densities
of N4 and S6 are 1.6075 and 1.7118, respectively. The intramolecular hyperconjugative
interactions energies are formed by the orbital overlap between π(C−C) and π*(C−C) bond
orbitals, which results intra molecular charge transfer (ICT) causing stabilization of the system.
The electron density (ED) of the three conjugated double bonds of the phenyl rings (~1.631e)
clearly demonstrates strong delocalization. Ravikumar et al., reported the electron density (ED) of
the six conjugated double bonds of the phenyl rings (∼1.661e) clearly demonstrates strong
delocalization for bis(4-nitrophenyl)carbonate [72]. The NBO analysis of donor-acceptor
interactions showed that the very small resonance for LP(S
σ*(C −S ) are 7.03, 7.24 and 5.52 kJ/mole, respectively. The orbital interaction energy between
π(C −O )→π*(C −C ), π(C −C )→π*(C10−C11) and π(C10−C11)→π*(C12−C15) are 451.29, 680.23
6
)→σ*(C
1
−C
2
), σ*(C
3
4
−N ) and
3
7
1
8
2
9
2
9
and 836.13 kJ/mole (Table. 2). The increasing interaction energies are due to strong ICT
interactions from rhodanine ring to the phenyl ring leading to the stabilization of the molecule.
4
.5 Molecular electrostatic potential
Electrostatic potential maps are very useful three dimensional diagrams of molecules. To
accurately analyze the charge distribution of a molecule, a very large quantity of electrostatic
10

potential energy values must be calculated. The best way to convey this data is to visually
represent it, as in an electrostatic potential map. Electrostatic potential correlates with dipole
moment, electronegativity, and partial charges. The Electrostatic Potential map of E5BTTO is
shown in Figure 5. It provides a visual method to understand the relative polarity of a molecule.
The importance of MEPs lies in the fact that it simultaneously displays molecular size, shape as
well as positive, negative and neutral electrostatic potential regions in terms of color grading and
is very useful in research of molecular structure with its physicochemical property relationship
[
73, 74]. MEP and electrostatic potential are useful quantities to illustrate the charge distributions
of molecules and used to visualize variably charged regions of a molecule. Therefore, the charge
distributions can give information about how the molecules interact with another molecule. MEP
is widely used as a reactivity map displaying most probable regions for the electrophilic attack of
charged point-like reagents on organic molecules [75]. The Molecular Electrostatic Potential
(
MEP) is the most useful electrostatic property to study the relation between structure and
activity. At any given point r(x,y,z) in the vicinity of a molecule, the electrostatic potential, V(r)
is defined in terms of the interaction energy between the electrical charge generated from the
molecule of electrons and nuclei and a positive test charge (a proton) located at r. The molecular
electrostatic potential (MEP) is related to the electronic density and a very useful descriptor for
determining sites for electrophilic attack and nucleophilic reactions as well as hydrogen-bonding
interactions [76, 77].
The MEP maps of the title molecule are shown in Figure 5, whereas electrophilic attack
is presented by negative (red) regions, nucleophilic reactivity is shown by the positive (blue)
regions of MEP map of E5BTTO. As seen from the Figure 5, the electrophilic region (red) is
around the phenyl ring and in ketone group of the rhodanine. Whereas the nucleophilic region
(
blue) is localized in N−H group of the rhodanine ring. The neutral sites of the molecule are
indicated by the green region. This predicted the most reactive site for both electrophilic and
nucleophilic attack.
4
.6 Mulliken atomic charges
The Mulliken charge is directly related to the vibrational properties of the molecule, and
quantifies how the electronic structure changes under atomic displacement; it is therefore related
directly to the chemical bonds present in the molecule. It affects dipole moment, polarizability,
electronic structure and more properties of molecular systems. Mulliken atomic charge
calculation has an important role in the application of quantum chemical calculation to molecular
system [78]. The Mulliken population analysis in E5BTTO molecule was calculated using
B3LYP level with 6-311++G(d,p) basis set. The Mulliken charge distribution structure of
E5BTTO is shown in Figure 6.
11

The Mulliken charges for the title compound are listed in Table 3. The charge distribution
of E5BTTO shows that the carbon atoms attached with hydrogen atoms are negative whereas the
other carbon atoms are positive. All hydrogen atoms are positively charged. The S, N and O
atoms shows negative charge and these represents the hydrogen bond acceptors. The hydrogen
atom attached to the nitrogen atom show higher positive charge than the other hydrogen atoms.
The Mulliken charge distribution shows the most negative charge observed at C12. The most
positive charge observed at C10 for the title molecule.
4
.7 Frontier molecular orbital analysis
The highest occupied molecular orbitals (HOMOs) and the lowest–lying unoccupied
molecular orbitals (LUMOs) are named as frontier molecular orbitals (FMOs). The FMOs play
an important role in the optical and electric properties, as well as in quantum chemistry and UV–
Vis. spectra [79]. The HOMO represents the ability to donate an electron, LUMO as an electron
acceptor represents the ability to obtain an electron. The energy gap between HOMO and LUMO
determines the kinetic stability, chemical reactivity and optical polarizability and chemical
hardness– softness of a molecule [80]. Considering the chemical hardness, large HOMO–LUMO
gap means a hard molecule and small HOMO–LUMO gap means a soft molecule. One can also
relate the stability of the molecule to hardness, which means that the molecule with least
HOMO–LUMO gap means it is more reactive.
The frontier molecular orbital analysis for the title molecule was calculated at the
B3LYP/6-311++G(d,p) level, which reveals that the energy gap reflects the chemical activity of
the molecule. The atomic orbital compositions of the frontier molecular orbitals are sketched in
Figure 7. The eigen values of LUMO and HOMO and their energy gap reflect the chemical
activity of the molecule. The HOMO is located over mainly in sulphur atom in rhodanine ring
and in carbon atoms in phenyl ring and the energy of HOMO level is 6.4712eV. The LUMO is
located all over the molecule and the energy is 3.0273eV. The energy gap of the title molecule is
3.4439eV.
HOMO
LUMO
=
=
=
6.4712eV
3.0273eV
3.4439eV
∆E
The calculated self-consistent field (SCF) energy of E5BTTO is -1311.47773452 kJ
−
1
mol . In addition, the energy gap of HOMO−1→LUMO+1 is 5.082 eV and the
HOMO−2→LUMO+2 is 7.4625 eV, respectively. Moreover, the lower in the HOMO and
LUMO energy gap explains the eventual charge transfer interactions taking place within the
molecule. The corresponding energy gap values are listed in Table 4.
12

4
.8 Thermodynamic properties
The statistical thermo chemical analysis of E5BTTO is carried out considering the
molecule to be at room temperature of 298.15 K and one atmospheric pressure. The
thermodynamic quantities such as entropy Stotal, heat capacity at constant pressure (Cp) total,
enthalpy (H–E)/T, Gibb’s free energy (G–E)/T and internal thermal energy (E) for various ranges
(
100–1000 K) of temperatures are determined and these results are presented in the Table 5.
From Table 5, it can be observed that these thermodynamic functions are increasing with
temperature ranging from 100 to 1000 K due to the fact that the molecular vibrational intensities
increase with temperature [81]. The variation of the thermodynamic functions such as entropy,
heat capacity, internal energy, enthalpy, and Gibb’s free energy with temperature are graphically
represented in Figure 8.
All the thermodynamic data supply helpful information for the further study on the
E5TTO. They can be used to compute the other thermodynamic energies according to
relationships of thermodynamic functions and estimate directions of chemical reactions
according to the second law of thermodynamics in thermochemical field.
5
. CONCLUSION
This work presents the experimental and theoretical vibrational IR and Raman spectra of
the title compound. All the vibrational bands, which are observed in the FT-IR and FT-Raman
spectra of the title compound, are completely assigned for the first time with the help of TED.
The observed FT-IR and FT-Raman spectral values were agree well with the calculated
wavenumber. The frontier molecular orbitals have been visualized and the HOMO–LUMO
energy gap (3.4439 eV) has been calculated. First hyperpolarizablity analysis reveals that the
title compound possesses considerable NLO properties. The NBO analysis have been made with
which the stability and intra molecular interactions have been interpreted and the transactions
give stabilization to the structure have been identified by second order perturbation energy
calculations. The Mulliken atomic charges of the present molecule has been calculated and also
plotted. Finally, the thermodynamic properties of the title compound have been calculated at
different temperatures and are plotted.
13

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18

Figure 1. The schematic diagram of synthesis of (E)-5-benzylidene-2-thioxothiazolidin-4-one

Figure 2. Optimized structure of (E)-5-benzylidene-2-thioxothiazolidin-4-one
E5BTTO)
(
20

Figure 3. The combined experimental and theoretical spectra of E5BTTO.
21

Figure 4. The combined experimental and theoretical spectra of E5BTTO
22

Figure 5. 3D mapped MEP surface of E5BTTO.
-
9.157e-2
9.157e-2
23

1.5
Mulliken/B3LYP
1.0
0.5
0.0
-0.5
Atoms
-1.0
Figure 6. The Mulliken atomic charges of E5BTTO
24

HOMO = 6.4712
HOMO-1 = 6.6589
HOMO-2 = 7.5553
∆E= 3.4439 eV
LUMO = 3.0273
LUMO+1 = 1.5769
LUMO+2 = 0.0928
Figure 7. The frontier molecular orbitals of E5BTTO
25

9
8
7
6
5
4
3
2
1
00
00
00
00
00
00
00
00
00
0
S
Cp
ddH
0
200
400
600
800
1000
Temperature
Figure 8. Thermodynamic parameters graph of E5BTTO.
26

Table 1. The experimental and calculated frequencies of E5BTTO using B3LYP/6-311++G(d,p) level of basis set [harmonic
−
frequency (cm ), IR, Raman intensities (Km/mol), reduced masses (amu) and force constants (mdynA° )].
1
−1
Calculated
Observed
Frequencies
(cm-1)
Mode
No
frequencies
(cm-1)
Un
Reduced Force
Masses Consts. Vibrational Assignments ≥ 10% TED
IR Intensity
Raman Intensity
FT-
Scaled Scaled FT-IR Raman Abs.
Rel.
Abs.
Rel.
1
2
3
4
5
6
7
8
9
3590
3237
3192
3181
3170
3161
3119
1757
1643
1620
1598
1523
1482
1449
1424
1368
1335
1280
1237
3450 3431m
3110
81.31 15.90
42.11
0.63
1.08
1.09
1.10
1.09
1.09
1.09
1.09
9.81
5.60
5.08
5.46
2.08
2.19
2.21
1.47
1.56
4.88
4.40
2.69
8.19
6.75
6.59
6.51
6.44
6.40
6.23
17.85
8.90
7.86
8.21
2.84
2.83
2.74
1.75
1.72
5.12
4.25
2.43
νN
4
H (100)
5
28.37
5.55
4.13
3.48
0.06
0.90
1.01
14.28
185.43
64.02
51.42
14.85
15.11
57.98
79.33
0.21
2.78
0.96
0.77
0.22
0.23
0.87
1.19
νC12
νC13
νC15
νC17
νC11
H16(99)
H18(96)
H19(93)
H20(93)
H14(91)
3067 3061vs 3065m 21.13
3057
3045
3037
2997
17.80
0.31
4.62
5.17
3015w
νC
νC
νC
9
H21(99)
1688 1697vs 1680w 266.28 52.06
1579 1589vs 1592vs 20.91 4.09
1 8
O (82)
1 2
C (82)
10
11
12
13
14
15
16
17
18
19
1557
1570vs 83.02 16.23 6667.56 100.00
91.61 17.91 5520.77 82.80
νC
9
C
2
(60)+βH21
17(45)+βH20
βH19
15(55)+βH18
C
9
C
2
(15)
1535
νC15C
C
17
C
15(12)
1464 1492m
6.84
1.34
2.42
416.79
521.85
6.25
7.83
7.72
C
15
C12(65)
1424 1435vs 1441vs 12.39
νC12C
C
13
C
17(18)
1393
325.04 63.55 514.51
νC
1
N
4
(28)+βC
1
N
4
H
5
(50)
1368
195.04 38.13 820.60 12.31
βH21
βH14
νC11
9 2
C C (58)
1314
1309m
4.79
0.94
2.12
54.69
0.82
6.24
6.68
C
11
C10(55)
1282 1296vs
10.84
416.30
C13(45)
1230 1236vs 1222m 70.74 13.83 445.64
νC
3
N
4
(27)+βC
1
N
4
C
3
(40)
1189 1190vs 1182s
17.13
3.35
848.56 12.73
νC10C11(40)
1

2
2
2
2
2
2
2
2
2
0
1
2
3
4
5
6
7
8
1219
1188
1184
1115
1072
1054
1024
1016
1000
1171
1141
1137
1160w
1.82
0.36
523.77
7.86
4.92
1.18
1.34
2.01
1.68
11.96
2.22
1.31
6.18
1.35
1.03
1.12
1.66
1.23
8.10
1.45
0.81
3.76
0.79
βH16
C
12
C
10(52)
17(50)
200.64 39.23 328.04
βH18C
13
C
511.44 100.00 776.49 11.65
νC
3
N
4
1
(14)+βC N
4
H
5
(18)+βH20
C C15(20)
17
1072 1068m 1067w 23.06
4.51
5.05
57.32
235.17
3.37
0.08
0.86
3.53
0.05
νC12
C
15(20)+βH20 15(26)
17
C C
1030
1029m 72.17 14.11
νC
3 7
S (42)+νC
3
S (22)
6
1013 1014m
4.06
0.60
1.06
0.12
0.79
0.12
0.21
0.02
νC17C
13(30)+βH18
13
C C17(12)
984
976
960
998s
τH16
C
12
C
15
H
19(77)+ГC17
βC12 17(50)
18(57)+ГC17
C
13
15
C H
20(15)
982.51 14.74
C C
15
3.20
0.05
2.12
τH14
C
11
C
13
H
C
13
15
C H
20(25)
νC
2
1
C (14)+νC
2
S
6
(12)+βC
βC
9
C
2
S
6
(18)+βC10
(16)
(28)+τH14
C
9
C (15)+
2
29
988
949
7.78
1.52
141.61
5.34
3.07
2
C
1
N
4
30
31
32
33
34
35
36
37
38
39
40
41
42
43
958
915
861
841
777
771
743
701
674
634
619
601
546
529
921
879
827
808
747
740
714
674
648
609
595
577
524
508
914m
8.87
9.60
1.73
1.88
0.23
1.28
3.65
1.04
9.07
6.03
9.67
0.53
5.14
27.44
1.62
0.08
0.41
0.02
4.69
0.26
0.33
0.01
0.01
1.81
1.13
0.25
0.66
2.88
0.03
1.44
1.36
1.25
6.18
1.88
5.17
5.90
1.93
8.67
6.51
1.11
7.17
16.51
8.86
0.78
0.67
0.55
2.58
0.67
1.81
1.92
0.56
2.32
1.54
0.25
1.52
2.90
1.46
ГC11C
10
C
13
H
14(15)+τH16
C
12
C
10
C
9
C
11
C H18(12)
13
851vw
9
ГC C
2
C
10
H
21(71)
1.16
ГC11
10
C C
13
H14(45)+τH16
C
12
C
10
C (35)
9
810vs
765vs
6.55
312.47
17.28
21.88
0.67
νC10
20(20)+τH16
(22)+βC10
(70)+ГC
9
C (16)+νC
2
S
6
(28)
(14)+τC10
(18)
18.65
5.32
ГC17C
C
13 15
H
C
12
C
10
C
9
C
12
C C15(12)
17
νC
2
C
1
9
C C
2
708w
673w
46.37
30.85
49.44
2.70
ГC
2 8
O
C
1 4
N
9 1
C C
2
S
6
(12)
675vs
634w
0.73
τC12C
15
C C17(42)
13
120.99
75.26
16.82
43.84
191.90
1.69
νC
2
C
1
(12)+νC
3
S
6
(48)+βC
2
1
C N
4
(10)
βC17C
13
C11(40)
67.66 13.23
5
τH N
4
C
1
C (92)
2
19.81
2.73
3.82
3.87
0.53
0.75
βC15C
17
C13(42)
524vs
521m
νC
3
N
4
(12)+νC
2
S
6
(28)+βC
2
C
1
4
N (30)
3
ГC S
6
N
S
4 7
(82)
2

4
4
4
4
4
4
5
6
7
8
517
506
433
420
373
276
275
263
201
137
118
497
486
416
404
358
265
264
253
193
131
113
43.09
6.33
4.55
0.16
0.75
5.43
0.37
3.78
0.01
3.18
0.63
8.42
1.24
164.30
17.67
2.46
0.27
7.41
3.14
22.33
3.04
4.25
13.26
4.66
7.87
7.44
10.46
7.73
1.17
0.47
2.46
0.32
0.35
0.59
0.21
0.32
0.18
0.12
0.06
βC
1
N
4
C
3
(12)+βC
15(15)+ГC
(18)+βC
2
C
1
O (35)
8
τC13
11
C C
17
C
9
C
10
C C11(45)
12
428m
434m
264m
0.89 1355.64 20.33
νC
2
C
1
(10)+νC
S
3 6
2
C
1
O
8
(16)+βC
3
S
6
C (25)
2
0.03
0.15
1.06
0.07
0.74
0.00
0.62
0.12
7.42
54.63
249.15
20.43
334.07
26.83
12.64
52.72
0.11
0.82
3.74
0.31
5.01
0.40
0.19
0.79
τC12
C
15
C C17(42)
13
τC10
C
C
12 17
C15(10)+ГC
2 8 1
O C N
4
(16)+ГC
9
1
C C
2
S (48)
6
4
9
0
βC C
9 2
6
S (12)+βS
C S
6 3 7
(40)+βC
3
S
6
C
2
(15)
(30)
(18)
5
τC10C
12
C
17
C
15(16)+τC10
9
C C
S
2 6
51
βC C
9 2
S
6
(12)+βC12
(14)+βC10
(72)+τC
(12)+βC10 (16)+βS
17(10)+τC10 (12)+τC
10 9
C C (15)+βS
6
C
3
S
7
52
βC C
9 2
S
6
9 2
C C (18)+βS
C
6 3
S
7
(15)
5
3
4
τC
1
N
4
C
2
S
6
2
C
1
S
6
C (16)
3
5
βC C
9 2
S
6
C C
9 2
6
C S
3
7
(14)
τC12C
15
C
13
C
τC
C
9
C
2
S
6
1
C
4
C
2
C (10)+
6
55
110
106
109m
62m
0.27
0.05
188.05
2.82
6.48
0.05
2 1
C C
3
S
6
(30)+ГC
9
C
10
12
C C11(20)
5
6
7
45
32
43
31
0.07
0.00
0.01
0.00
211.54
49.14
3.17
0.74
6.38
6.91
0.01
0.00
τC
2
C
9
10
C C
12(32)+τC10
C
C S
9 2 6
(41)+τC
1
C
4
S
6
3
C (12)
5
τC
2
C
9
10
C C
12(40)+τC
C S C
1 4 6 3
(24)+ГC
9
C
1
S
6
2
C (25)
ν: Stretching, δ: in-plane-bending, Γ: out-of-plane bending, vw: very week, w:week, m:medium, s:strong, vs:very strong,
a
Scaling factor: 0.9608,
b
Relative IR absorption intensities normalized with highest peak absorption equal to 100,
c
Relative Raman intensities calculated by Equation (1) and normalized to 100.
d
Total energy distribution calculated at B3LYP/6-311++G(d,p) level.
3