Vibrational and quantum chemical investigation of cyclization of thiosemicarbazide group in 1-benzoyl-4-phenyl-3-thiosemicarbazide

Article abstract of DOI:10.1016/j.saa.2014.03.095

1-Benzoyl-4-phenyl-3-thiosemicarbazide (H₃bpt) was treated with acid - base in one sequence and base - acid in other sequence, both of which lead to ring formation of thiosemicarbazide group, giving N-phenyl-5-phenyl-1,3, 4-thiadiazol-2-amine (Hppta) in the first case and 4,5-diphenyl-2,4-dihydro-1,2, 4-triazole-3-thione (Hdptt) in the second case. The primary (H₃bpt) as well as the resulting compounds (Hppta & Hdptt) has been characterized by elemental analyses, NMR, FTIR and Raman spectroscopic techniques. The quantum chemical calculations of the compounds are performed using DFT/B3LYP/6311G(d,p) method for geometry optimizations and also for prediction of the molecular properties. The cyclization is confirmed by disappearance of many bands belonging to the open chain subgroups of H₃bpt such as; NH stretching, NH bending, CN stretching, NH puckering, CO stretching etc. The ring formation of 1-benzoyl-4-phenyl-3-thiosemicarbazide (H₃bpt) has been further confirmed by the appearance of many bands belonging to the closed ring of thiosemicarbazide in the resulting compounds Hppta and Hdptt.

Full text of DOI:10.1016/j.saa.2014.03.095

Accepted Manuscript
Vibrational and Quantum Chemical investigation of cyclization of thiosemicar-
bazide group in 1-benzoyl-4-phenyl-3- thiosemicarbazide
Priyanka Gautam, Om Prakash, R.K. Dani, N.K. Singh, Ranjan K. Singh
PII:
S1386-1425(14)00506-X
http://dx.doi.org/10.1016/j.saa.2014.03.095
SAA 11928
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
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Revised Date:
Accepted Date:
25 October 2013
28 February 2014
18 March 2014
Please cite this article as: P. Gautam, O. Prakash, R.K. Dani, N.K. Singh, R.K. Singh, Vibrational and Quantum
Chemical investigation of cyclization of thiosemicarbazide group in 1-benzoyl-4-phenyl-3- thiosemicarbazide,
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.
2014.03.095
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Vibrational and Quantum Chemical investigation of cyclization of
thiosemicarbazide group in 1-benzoyl-4-phenyl-3- thiosemicarbazide
Priyanka Gautama, Om Prakasha, R.K. Danib, N.K. Singhb, Ranjan K. Singha*
aDepartment of Physics, Banaras Hindu University, Varanasi- 221005, India.
bDepartment of Chemistry, Banaras Hindu University, Varanasi- 221005, India
Abstract
1-benzoyl-4-phenyl-3-thiosemicarbazide (H3bpt) was treated with acid - base in one
sequence and base – acid in other sequence, both of which lead to ring formation of
thiosemicarbazide group, giving N-phenyl-5-phenyl-1,3,4-thiadiazol-2-amine (Hppta) in the
first case and 4,5-diphenyl-2,4-dihydro-1,2,4-triazole-3-thione (Hdptt) in the second case.
The primary (H3bpt) as well as the resulting compounds (Hppta & Hdptt) has been
characterized by elemental analyses, NMR, FTIR and Raman spectroscopic techniques. The
quantum chemical calculations of the compounds are performed using
DFT/B3LYP/6311G(d,p) method for geometry optimizations and also for prediction of the
molecular properties. The cyclization is confirmed by disappearance of many bands
belonging to the open chain subgroups of H3bpt such as; N-H stretching, N-H bending, C-N
stretching, N-H puckering, C=O stretching etc. The ring formation of 1-benzoyl-4-phenyl-3-
thiosemicarbazide (H3bpt) has been further confirmed by the appearance of many bands
belonging to the closed ring of thiosemicarbazide in the resulting compounds Hppta and
Hdptt.
Keywords: Thiosemicarbazide, Thiadiazole, Triazole, FT-IR, Raman and DFT.
*Correpsondence author e-mail: ranjanksingh65@rediffmail.com

1. Introduction:
Heterocyclic aromatic compounds contained N, S and O in the ring are biologically active
and pharmaceutically important [1-5]. The derivatives of triazole and thiadiazole have been
found to possess a wide spectrum of pharmacological, medical and biological activities [6-
9]. The derivatives of triazole and thiadiazole could be synthesized from the derivatives of
1-benzoyl-3-thiosemicarbazide followed by ring formation of thiosemicarbazide group by
treating with acid followed by base or base followed by acid [10-12]. The
thiosemicarbazides being building blocks for the synthesis of a variety of heterocyclic ring
compounds is useful to design therapeutically useful drugs. The ring formation and opening
mechanisms are important and crucial because a drug in open or closed chain form affects
biologically induced reaction and metabolic process differently. The cyclization/
decyclization phenomena in vivo is generally induced by catalyst. However, it can be
induced by varying temperature/ pH of the medium [13-15]. The FTIR and Raman
spectroscopy combined with quantum chemical computation may give fingerprint of this
process.
The main purpose of this work is to investigate the ring formation phenomenon of
thiosemicarbazide group of the 1-benzoyl-4-phenyl-3-thiosemicarbazide, resulting the
molecules N-phenyl-5-phenyl-1,3,4-thiadiazole-2-amine and 4,5-diphenyl-2,4-dihydro-
1,2,4-triazole-3-thione, by the means of combined FTIR, Raman and DFT technique and
elucidate the structural information with molecular properties. The quantum chemical
calculation of the compounds are performed using DFT/B3LYP/6311G(d,p) method [16-18]
for geometry optimizations and also for prediction of the molecular properties viz. charge
distribution, molecular electrostatic potentials surfaces, frontier molecular orbital and
reactive sites for electrophilic attack and neucleophilic reaction. The vibrational assignments

of the IR and Raman bands are carried out by using GAR2PED software [19]. We also made
the comparisons between experimental results with computed one.
2. Experimental:
2.1 Materials: Methyl benzoate, Phenyl isothiocyanate (Sigma Aldrich), Conc. H2SO4 (SD
Fine Chemicals) and NaOH, hydrazine hydrate (Qualigens) were used. The reagents were
used without further purification and all experiments. All the synthetic manipulations were
carried out in open atmosphere and at room temperature. The solvents were dried and
distilled before use following the standard procedure.
2.2 Synthesis:
2.2.1: 1-benzoyl-4-phenyl-3-thiosemicarbazide (H3bpt): A mixture of benzoic acid
hydrazide (2.160 g, 20 mmol) and phenyl isothiocyanate (2.4 mL, 20 mmol) in benzene was
refluxed for 8 h at 80 ºC, from which white precipitate of 1-benzoyl-4-phenyl-3-
thiosemicarbazide was obtained after cooling. The precipitate was filtered off, washed with
water and diethyl ether, air dried and crystallized from ethanol.
2.2.2:
N-phenyl-5-phenyl-1,3,4-thiadiazole-2-amine (Hppta): 1-benzoyl-4-phenyl-3-
thiosemicarbazide (2.813 g, 10 mmol) was added slowly in 10 ml conc. H2SO4 and stirred
for 2 h at low temperature. The mixture was poured over crushed ice and the precipitated
solid was filtered off, washed twice with cold water and dried. The yellow compounds were
obtained by slow evaporation of solvent for 15 days.
2.2.3: 4,5-diphenyl-2,4-dihydro-1,2,4-triazole-3-thione (Hdptt): A stirring mixture of 1-
benzoyl-4-phenyl-3-thiosemicarbazide (2.813 g, 10 mmol) and NaOH (0.4 g, 10 mmol) in
ethanol 25 mL was refluxed for 6 h at 65 ºC. After cooling, the solution was acidified with
dil. HCl (6 mL, 30%, v/v) and the precipitate of 4,5-diphenyl-2,4-dihydro-1,2,4-triazole-3-
thione was filtered off and crystallized from ethanol.

The synthesis of compounds H3bpt, Hppta and Hdptt are depicted in scheme 1 (in
supplementary part).
2.3. Instrumentation and measurements: Carbon, hydrogen and nitrogen contents were
estimated on an Elementar Vario EL III Carlo Erbo 1108. FT-IR spectra were recorded in
the 4000–400 cm-1 region in KBr pellets on Spectrum 65 FT-IR spectrometer from
1
13
PerkinElmer. H and C NMR spectra were recorded in DMSO-d6 on a JEOL AL300 FT
NMR spectrometer using TMS as an internal reference. Initially benzoic acid hydrazide was
prepared by refluxing equimolar amount of methyl benzoate and hydrazine hydrate at 75 ºC
for 5h.
The laser Raman spectra were recorded on a Raman spectrometer from Renishaw
Model: RM 1000 having grating of 2400 grooves/mm giving spectral resolution of ~1 cm-1
at 50 micron slit opening. The 514.5 nm Ar+ -laser was used as an excitation source
delivering ~5 mW intensity at the sample. A microscope from Olympus with 50 x objectives
was used to focus the laser on the sample and to collect the Raman scattered signal in back
scattering geometry. The Raman spectra were recorded in the range 200-3500 cm-1.
Spectrometer scanning, data collection and processing were done by a dedicated computer
using Gram Wire software.
3. Computational details:
All quantum chemical calculations and the geometry optimization of compounds
H3bpt, Hppta and Hdptt have been performed with Gaussian 03 and GaussView 4.1 program
packages [20]. The optimization of the compounds have been done using DFT method with
functional B3LYP and basis set 6-311G (d,p) [16-18]. The frequency calculations were also
performed using the same level of theory. The absence of imaginary harmonic frequencies
confirms that the optimized structures are the global minimum energy conformations. The

assignments of the vibrational modes were done by using GAR2PED software [19]. In
addition to this the electrostatic potential mapping surfaces (MEPS) and HOMO-LUMO
scheme were also plotted for more clear presentation regarding the charge distributions and
reactive site of the molecules by the same DFT/B3LYP/6-311G (d,p) method at the 0.02
isovalues and 0.0004 isodensity value.
4. Results and discussion:
4.1 Synthetic characterizations of compounds:
The analytical Data, Colour, Melting Point and Percentage Yield of H3bpt, Hppta and Hdptt
are shown in table [1] and NMR results are summarized as follow.
1
H3bpt: H NMR (DMSO-d6, δ, ppm): [7.62 (2H), 7.35 (1H), 7.14 (2H)] phenyl ring; 11.84
13
(s, 3H, NH). C NMR (DMSO-d6, δ, ppm): 201.05 (>C=S), 163.90 (>C=O) and [144.58-
123.27] phenyl ring.
1
Hppta: H NMR (DMSO-d6, δ, ppm): [7.68 (2H), 7.27 (1H), 7.12 (2H)] phenyl ring; 5.23
13
(1H, NH). C NMR (DMSO-d6, δ, ppm): [142.68-122.17] phenyl ring and [173.74 C(1),
152.94 C(2)] thiadiazole carbons.
1
Hdptt: H NMR (DMSO-d6, δ, ppm): [7.70 (2H), 7.43 (1H), 7.10 (2H)] phenyl ring; 8.46
13
(1H, NH). C NMR (DMSO-d6, δ, ppm): [143.63-121.79] phenyl ring and [201.07 C=S,
154.87 C2] triazole carbons.
4.2 Molecular Geometry: The optimized molecular structures of the compounds H3bpt,
Hppta and Hdptt are shown in figures S1 (a), (b) & (c) respectively (in supplementary part).
The calculated bond distances and bond angles participating in the ring formation have been
compared with that of experimental values observed for the structurally related compounds
[21-23] and the results are given in table 2(a), (b). The slight deviations between the

calculated and experimental geometric parameters is due to the fact that the theoretical
calculations belong to isolated molecule in gaseous phase while the experimental results
belongs to molecule in solid state and the existence of the intermolecular interactions which
connects the molecules together. Here, in our case the molecules in present study are not
exactly same with those experimentally observed molecules, undertaken for comparisons.
These are the main causes for such deviations. The Mulliken’s charge on the atoms
participating in the ring formation is listed in the table 2(c). The energies of optimized
structures of H3bpt, Hppta and Hdptt are -32087.877 eV, -30006.914 eV and -30007.445 eV
respectively and the dipole moments (in Debye) are 1.1739 D, 3.1613 D and 5.1288 D
respectively with same point groups C1.
4.3 Molecular properties:
4.3.1 Molecular electrostatic potential (MEP) and Frontier molecular orbital (FMO)
analysis:
The Molecular Electrostatic Potential (MEP) is the most useful to study structure-reactivity
relationship of the molecules [24]. The molecular electrostatic potential (MEP) is related to
the electronic density and a very useful descriptor for determining the sites for electrophilic
attack and nucleophilic reaction as well as hydrogen-bonding interactions [25, 26]. The MEP
maps of molecules H3bpt, Hppta and Hdptt are shown in figures S1 (a), (b), & (c) (in
supplementary part). The electrophilic attack is illustrated by red (negative) regions whereas
nucleophilic reactivity is shown by the blue (positive) regions and the green region cover the
parts of the molecule where electrostatic potentials are close to zero. In figure (1), the region
for electrophilic attack(red) is mainly localized on the oxygen atom of benzoyl group and
weak electrophilic attack(yellow) is localized on the sulphur atom of thiosemicarbazide
group whereas the nucleophilic reactivity of the molecule is mainly localized on the surface
of H atoms bound to nitrogen of thiosemicarbazide group in H3bpt. After the ring formation

phenomenon, sites for electrophilic attack and nucleophilic reaction changed as shown in
figure (1). In case of Hppta, the region for electrophilic attack (red) is localized on the
nitrogen atoms of thiadiazole ring, whereas the nucleophilic reactivity is localized on the
surface of H atoms bound to nitrogen of amine group. Similarly the region for electrophilic
attack (red+yellow) is localized on the sulphur atom of 1,2,4-triazole-3-thione ring and weak
electrophilic attack(yellow) is localized on the nitrogen atom (free from H) of 1,2,4-triazole
ring, whereas the nucleophilic reactivity is localized on the surface of H atoms bound to
nitrogen of 1,2,4-triazole ring in Hdptt. The frontier molecular orbital can offer a reasonable
qualitative prediction of the excitation properties. The energy gap between HOMO and
LUMO is a critical parameter to predict molecular electrical transport properties. The
HOMO energy characterizes the electron donating ability and the LUMO energy
characterizes the electron accepting ability, and the HOMO-LUMO energy gap characterizes
the molecular chemical stability and this energy gap are also responsible for spectroscopic
properties of the molecules [27-28]. The energies of the HOMO and LUMO orbitals of
molecules H3bpt, Hppta and Hdptt were investigated using the DFT/B3LYP method. Figure
S2 (in supplementary part) shows the isodensity surface plots of HOMO and LUMO and
energy excitation scheme from the ground state (HOMO) to the first excited state (LUMO).
The electronic transition from the ground state to the excited state due to a transfer of
electrons from the HOMO to LUMO levels is mainly due to π∙∙∙π transition. The positive
phases are red and the negative ones are green. The small energy gap of molecules is termed
as soft while the large energy gaps are termed as hard molecules. The hardness value (η) of a
molecule can be defined by the formula [28].
η = {-εHOMO + εLUMO}/2

where εHOMO and εLUMO are the energies of the HOMO and LUMO molecular
orbitals. The soft molecules are high reactive, high polarisable and less stable than the hard
ones because soft molecules need small energy for excitation.
4.3.2 Analysis of global and local reactivity descriptors:
The global chemical reactivity of molecules have been defined in terms of hardness (η),
softness (S), chemical potential (µ), electronegativity (χ) and electrophilicity index (ω) and
local reactivity has been defined in terms of Fukui function and the philicity [29-32]. Using
Koopman’s theorem for closed-shell molecules, η, S, µ, χ and ω are related as:
ω = µ2 /2η
I = - EHOMO and A = - ELUMO
where I and A are the ionization potential and electron affinity of the compounds. χ is the
Mulliken electronegativity, because of the fundamental relationship to the chemical potential,
therefore χ is a property of the entire molecule [31]. In the reference global chemical
reactivity of molecules, the electrophilicity index (ω) is the most important descriptor. It is a
measure of energy lowering due to maximal electron flow between donor and acceptor [30].
Thus global and local chemical reactivity descriptors of molecules are very useful parameters
to define the intensity of chemical reactivity and site selectivity. Therefore by calculating
these parameters, we can explain theoretically the biologically active properties of molecules.
All the calculated values of ionization potential, electron affinity, hardness, potential, softness
and electrophilicity index are shown in table 3.

4.4 FTIR and Raman band analysis:
We focused mainly on those vibrational modes of molecules that belong to the groups
participating in the ring formation phenomenon. For clear presentation the spectra are
presented in many wavenumber regions. A summary of these vibrational bands (Infrared and
Raman) along with the DFT calculated bands with assignments for the molecules H3bpt,
Hppta and Hdptt are listed in table 4(a), (b) & (c) respectively.
N–H stretching Region:
The N–H stretching vibrations were observed only in experimental IR at 3451 cm-1 for
H3bpt, which was calculated theoretically at 3452 cm-1. It disappeared in the Hppta and
Hdptt as a result of removal of H atom from –N site due to ring formation of H3bpt. It is a
clear signature of cyclization of H3bpt. There are three N-H groups in H3bpt but only one IR
band corresponding to ν(N4-H5) is observed. In Hppta, H5-atom of N4-H5 is removed on ring
formation and therefore the N-H stretching disappears. On the other hand, in Hdptt, other
two H-atoms of N-H bond are removed due to ring formation. Normally, we should expect
ν(N7-H8) to appear in Hppta and ν(N4-H5) in Hdptt. However, it does not appear in Hppta.
This is the most probably due to the complex H-bonds [33-34]. This complex H-bonds is
because of the formation of supramolecular architecture of molecules through intermolecular
hydrogen bonding, therefore ν(N–H) bond is weakened and finally result no experimental
wave number. But it appears at ~3663 cm-1 in case of Hdptt. This ν(N–H) band is calculated
at 3635 and 3668 cm-1 by using DFT method for an isolated molecule of Hppta and Hdptt
respectively in the gaseous phase.
C–H stretching Region:

This C–H stretching modes are indirectly affected due to ring formation. Small changes are
therefore expected in (C-H) vibrations during H3bpt  Hppta and H3bpt  Hdptt
conversions. There are two (C-H) Raman bands at 3181 and 3163 cm-1 of H3bpt and no IR
band. The (C-H) mode is Raman active and IR inactive in H3bpt. Whereas in Hppta it is
strong IR as well as Raman active; giving a number of IR bands at ~ 3232, 3210, 3190,
3179, 3164 and 3137 cm-1 and Raman bands at ~ 3220, 3237, 3295, 3200, 3168, 3144,
3100, 3066 and 3046 cm-1. Like H3bpt the (C-H) mode Raman active and IR inactive in
Hdptt giving Raman bands at 3111, 3072, 3048 and 3033 cm-1.
C=O stretching, N-H bending and C=N stretching Regions:
The ν(C=O) band is observed weakly at 1721 cm-1 in the Raman spectra of H3bpt and it
disappeared completely in Raman spectra of Hppta and Hdptt due to removal of H2O after
the ring formation of H3bpt. The Raman bands at 1595 cm-1 and 1560 cm-1 and IR bands at
1598 cm-1 and 1553 cm-1 of H3bpt are attributed to β(N10-H11) + β(N4-H5) and β(N6-H7) of
thiosemicarbazide group of H3bpt. After the ring formation during H3bpt  Hppta and
H3bpt  Hdptt conversions, the two Raman bands corresponding to β(N10-H11) plus β(N4-
H5) and β(N6-H7) of thiosemicarbazide group and IR bands at ~1598 cm-1 [β(N10-H11)] are
disappeared whereas IR band at ~ 1553 cm-1 is red shifted to ~ 1534 cm-1 with small
contribution of β(N6-H7). This red shift is due to new vibrational mode; ν(C2=N3)+ν(C5=N4),
a characteristic band of thiadiazole ring. Further we observed a Raman band at 1519 cm-1
and an IR band at 1513 cm-1 assigned as ν(C2=N3) [thd], which give the clear evidence of
ring formation and converted into the thiadiazole ring. Similarly in the spectral analysis
Hdptt, the bands corresponding to β(N10-H11) plus β(N4-H5) and β(N6-H7) of
thiosemicarbazide group/chain are disappeared in IR as well as Raman spectra. But a sharp
Raman band at ~1583 cm-1 and a IR band at ~1585 cm-1 are appeared due to ν(C2=N3), a

characteristic band of triazole ring [trz]. The IR band at ~1492 cm-1 of Hdptt is attributed to
β(N4-H5). A single band at 1428 cm-1 in IR spectra and couple of Raman bands at 1443 cm-1
and 1453 cm-1 of Hdptt are appeared newly. On the basis of DFT calculation these bands are
assigned as mixed contribution of ν(C2=N8) and τ(Rtrz) which give the clear evidence of ring
formation and converted into the triazole ring. The bands define the existence of
thiosemicarbazide group/chain i.e. characteristic bands, appeared at ~ 1407 cm-1 (strong) in
Raman and at ~1406 cm-1 in IR spectra of H3bpt and these are assigned as contribution of
total possible vibrational modes thiosemicarbazide group/chain as shown in table 4 (a).
These bands are completely disappeared in Raman as well as in IR spectra of both Hppta
and Hdptt. This confirms that no more existence of thiosemicarbazide group/chain with aid
of acid or base and ring formation of H3bpt resulting Hppta and Hdptt.
C-N, C-S and N-N stretching Regions:
In the vibrational spectral analysis of H3bpt, we observed a Raman band at ~1380 cm-1 and
corresponding an IR band at 1383 cm-1, attributed to ν(C8-N10)+ ν(C8-N6) and ν(C8-S9).
Subsequently, a Raman band at ~1308 cm-1 and an IR band at ~1307 cm-1 are also appeared
due to mixed contribution of vibrational modes of thiosemicarbazide + C=O + C=C as
shown in table 4(a). These are the characteristic modes to define the open character of
thiosemicarbazide in H3bpt. But these bands are completely diminished in the Raman as
well as in IR spectra after the ring formation of H3bpt and change into the thiadiazole ring
(Hppta) and triazole-thione ring (Hdptt) on the removal of water molecule in both cases.
Since (C-N)+(N-H) bonds [figure 1(a), (b) & (c)] present in all the three molecules,
therefore there is certain possibility to show the effect of red shift or blue shift due to the
change in structure and thus due to change in the charge distribution. In this reference , we
observed that the Raman band at ~1246 cm-1 and IR band at ~1254 cm-1 [ν(C12-N10)+β(N10-

H11)] of H3bpt is red shifted in case of Hppta, at ~1243 cm-1(Raman) and 1247 cm-1(IR)
[ν(C9-N7)+β(N7-H8)] respectively. Whereas in case of Hdptt, a Raman band (1267 cm-1) and
an IR(1270 cm-1) are appeared with vibrational modes of triazole ring [ν(C6-N4)+v(N4-N3)]
and β(N4-H5) with ν(C6-S7) as given in table 4 (b) & (c). Further, we observed stretching
modes of (N-N) present in the thiadiazole ring of Hppta and triazole ring of Hdptt most
significantly, which are the characteristic modes of ring formed. In the Raman spectra of
Hppta, two bands at ~ 1149 cm-1 and 1103 cm-1 are assigned as ν(N-N), whereas in the IR
spectra these two are appeared at ~1141 cm-1 and 1100 cm-1. Similarly, In the Raman spectra
of Hdptt, two bands at ~ 1154 cm-1 and 1120 cm-1 are assigned as ν(N-N), whereas in the IR
spectra these are appeared at ~1146 cm-1, 1116, and 1102 cm-1.
Low wavenumber Regions:
This section contains mainly bending types of the vibartional modes viz. bending (–out of
plane, -in plane, linear), scissoring, torsion, deformation, rocking and puckering with very
small contribution of stretching modes of [thiosemicarbazide + (C=O)] group. The
prominent Raman band at ~ 931 cm-1/ IR band at ~ 934 cm-1 associated with various
bending type vibrations of linking chain between two benzene rings [table 4(a)] is
characteristic of H3bpt, which also disappeared in Hppta and Hdptt (Fig.1). The region 900 –
650 cm-1 mainly belongs to the vibrational modes of βOUT(C-H) of the benzene ring. But in
addition to βOUT(C-H), the bands corresponding to the vibrational modes of β(C=O), β(C-S),
ν(C-S), deformation of (C-N-N) bond and ring puckering of benzene ring are observed
significantly as listed in table 4(a). The ring closure in H3bpt influences the band shape of
benzene ring modes because of charge shift in the process to attain new stable configuration;
Hppta and Hdptt. Subsequently, the lower wavenumber region 550-200 cm-1 belongs to the
torsion modes of ring. Two Raman at 459 cm-1, 236 cm-1 and IR band at 459 cm-1 are

attributed to torsion modes of benzene and thiadiazole rings in the spectra of Hppta [table
4(b)]. Similarly the Raman bands at 408 cm-1, 362 cm-1, 337 cm-1 and 324 cm-1 are assigned
as torsion modes of benzene and trizole rings [table4(c)]. Before the ring formation in H3bpt,
these bands are observed at 423 cm-1 and 412 cm-1 in the IR spectra of H3bpt and assigned as
shown in table 4(a). However corresponding to these modes, no Raman band is appeared. In
the Raman spectra of H3bpt, three marker bands are observed at 327 cm-1, 273 cm-1 and 238
cm-1, which give the clear Raman signature of the presence of open chain character
[thiosemicarbazide + (C=O)] of H3bpt. The bands at 327 cm-1, 273 cm-1 and 238 cm-1 are
assigned as given in table 4(a). Since [thiosemicarbazide + (C=O)] of H3bpt converted in
thiadiazole and triazole-thione rings respectively in Hppta and Hdptt after removal of water
molecule, therefore the Raman bands at 327 cm-1, 273 cm-1 and 238 cm-1 of H3bpt
disappeared and new bands appeared corresponding to the modes of thiadiazole and triazole-
thione rings.
5. Conclusions
The present work reports synthesis and spectroscopic studies of three compounds. It has
been observed that on treatment of 1-benzoyl-4-phenyl-3-thiosemicarbazide with acid/ base
followed by neutralisation process with base/ acid, thiosemicarbazide group is able to
cyclise in two different ways leading to formation of thiadiazole and triazole rings. The
cyclization is well characterized by FT-IR, Raman and DFT study. The cyclization is
confirmed by disappearance of many bands belonging to the open chain subgroups of H3bpt
such as; N-H stretching, N-H bending, C-N stretching, N-H puckering, C=O stretching etc.
The cyclization of thiosemicarbazide group of H3bpt has also been confirmed by the
appearance of many bands belonging to thiadiazole and triazole rings of resulting
compounds Hppta and Hdptt respectively. The calculated geometrical parameters of each

compounds using DFT/B3LYP/6-311G(d,p) method are found in nice agreement with
experimental results. The MEP and FMO analysis were done by the same DFT method. In
addition to this, the global chemical reactivity of molecules has also been investigated. The
energies of HOMO and LUMO are negative, which indicate that all are the stable
compounds.
Acknowledgement
PG (Junior Research Fellow) and Om Prakash are grateful to the UGC, India for providing
research fellowship. RKS is grateful to AvH Foundation, Germany, and DST and CSIR, New
Delhi for support to procure micro-Raman setup. Authors are also grateful to biophysics lab;
department of Physics and department of Chemistry, BHU, Varanasi-221005, for providing
lab facilities.
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Figure Captions:
Figure 1(a): Optimized structure and MEP surface map of H3bpt.
Figure 1(b): Optimized structure and MEP surface map of Hppta.
Figure 1(c): Optimized structure and MEP surface map of Hdptt.
Figure 2: The HOMO-LUMO plots for the (a) H3bpt, (b) Hppta and (c) Hdptt.
Figure 3(a): Experimental FT-IR and Raman spectra of H3bpt.

Figure 3(b): Experimental FT-IR and Raman spectra of Hppta.
Figure 3(c): Experimental FT-IR and Raman spectra of Hdptt.
Tables Captions:
Table 1: Analytical Data: Empirical formulae, Color, Melting Point, & Percentage Yield of
H3bpt, Hppta and Hdptt and elemental analysis.
Table 2(a): Selected bond lengths of H3bpt, Hppta and Hdptt calculated by DFT method with
experimental results [21, 22 and 23].
Table 2(b): Selected bond angles of H3bpt, Hppta and Hdptt calculated by DFT method with
experimental results [21, 22 and 23].
Table 2(c): Mulliken’s charge on the selected atoms of of H3bpt, Hppta and Hdptt calculated
by DFT method.
Table 3: Global reactivity descriptors and other parameters related to molecular properties
calculated by DFT method:
Table 4(a): Calculated and experimental wavenumbers (in cm-1) and their tentative
vibrational assignmentsa (PED) of H3bpt. (wavenumbers less than 200 cm-1 are not included):
Table 4(b): Calculated and experimental wavenumbers (in cm-1) and their tentative
vibrational assignmentsa (PED) of Hppta. (wavenumbers less than 200 cm-1 are not included):
Table 4(c): Calculated and experimental wavenumbers (in cm-1) and their tentative
vibrational assignmentsa (PED) of Hdptt. (wavenumbers less than 200 cm-1 are not included):

Figure 1

Figure 2

Figure 3(a)

Figure 3(b)

Figure 3(c)

Table 1
Table 1:
S. No.
Empirical formula
(Weight in gm.)
M.P.(0C)
Color
Yield
Elemental Analysis %Found (calc.)
(%) (gm)
C
H
N
S
(1)
(2)
C14H13N3SO
(281.34)
142
176
White
86
78
59.75
4.68
18.47
(18.50)
19.79
(19.75)
11.38
(11.36)
12.20
(12.18)
( 59.77)
63.88
( 4.66)
4.23
C14H11N3S
Dirty white
(63.86)
(4.21)
(263.33)
C14H11N3S
214
Yellow
82
63.90
4.22
19.77
12.21
(3)
(63.86)
(4.21)
(19.75)
(12.18)
(263.33)

Table 2(a)
Table 2(a)
No.
H3bpt
N4-H5
N4-N6
N6-H7
N6-C8
S9-C8
Calc.
1.019
1.388
1.018
1.366
1.680
1.370
1.011
1.490
1.415
1.372
1.226
Expt.(21) Hppta
Calc.
1.396
1.304
1.396
1.357
1.667
1.362
1.434
1.470
1.007
Expt.(22)
1.372
1.300
1.367
1.329
1.679
1.375
1.466
1.472
Hdptt
C2-S6
C2=N3
C5=N4
C5-S6
C5-N7
N4-N3
C9-N7
N7-H8
C2-C1
Calc.
1.778
1.295
1.304
1.769
1.365
1.360
1.409
1.007
1.466
Expt.(23)
1.729
1.291
1.309
1.741
1.353
1.388
1.415
1.
2.
l.000
1.418
0.910
1.363
1.692
1.314
0.860
C2-N8
C2=N3
C6-N8
C6-N4
C6-S7
N4-N3
N8-C9
C2-C1
H5-N4
3.
4.
5.
6.
C8-N10
N10-H11
C1-C2
C12-N10
C2-N4
C2=O3
7.
8.
9.
10.
11.

Table 2(b)
Table 2(b)
No.
1.
H3bpt
Calc.
Expt.(21)
1 13.00
114.50
116.00
114.00
139.20
121.00
117.00
124.50
Hppta
Calc.
Expt.(22)
125.06
124.23
127.23
128.74
127.30
Hdptt
Calc.
Expt.(23)
87.5
N4-N6-H7
N6-C8-N10
H5-N4-N6
C8-N10-H11
N4-N6-C8
N6-C8-S9
H7-N6-C8
S9-C8-N10
C12-N10-H11
C2-N4- N6
C1-C2-N4
N4-C2 =O3
C1-C2=O3
C2-N4- H5
C12-N10-C8
109.92
111.14
111.79
114.74
120.31
121.74
122.56
127.06
113.59
115.65
116.01
120.31
123.66
124.44
130.72
N3=C2-C1
N8-C2-C1
C2-N8-C9
N4-C6-S7
N8-C6-S7
N8-C6-N4
C2=N3-N4
C2-N8-C6
N8-C2=N3
C6-N4-N3
H5-N4-N3
C6-N8-C9
C6-N4-H5
122.46
126.89
127.79
127.95
130.12
101.93
104.59
108.05
110.65
114.79
120.73
123.82
124.48
C2-S6-C5
C5=N4-N3
N4=C5-S6
C2=N3-N4
S6-C5-N7
N4=C5-N3
C5-N7-C9
N3=C2-S6
C9-N7-H8
C5-N7-H8
C1-C2-S6
N3=C2-C1
85.81
2.
112.81
113.76
115.06
119.8
111.8
113.4
114.0
120.5
126.1
128.0
3.
4.
5.
6.
126.45
129.56
112.56
114.73
115.71
123.14
124.3
7.
8.
9.
10.
11.
12.
13.
14.
15.

Table 2(c)
Table 2(c)
No.
1.
H3bpt
N10
H11
C8
Charge
-0.457
0.226
0.208
-0.252
-0.272
0.242
-0.284
0.269
0.451
-.0394
-0.189
0.186
Hppta
N7
Charge
-0.473
0.237
Hdptt
S7
Charge
-0.242
0.154
2.
H8
C6
3.
C5
0.219
N4
H5
N3
C2
-0.243
0.269
4.
S9
S6
0.181
5.
N6
C2
-0.003
-0.190
-0.242
-0.064
0.167
-0.205
0.368
6.
H7
N3
7.
N4
N4
N8
C9
-0.459
0.057
8.
H5
C1
9.
C2
C9
C1
-0.134
10.
11.
12.
O3
C1
C12

Table 3
Table 3:
Molecular Properties
Ionization potential (I)
Electron affinity (A)
Global hardness()
H3bpt
6.20
Hppta
5.67
Hdptt
5.80
1.65
1.47
1.68
2.275
0.440
3.925
-3.925
3.386
2.1
2.06
Global softness (s)
0.476
3.57
0.486
3.74
Electronegativity ()
Chemical potential ()
Global electrophilicity ()
-3.57
3.035
-3.74
3.395