Synthesis, crystal structure, and spectroscopic and electronic properties of N-[4-(3-Methyl-3-Phenyl-Cyclobutyl)-Thiazol-2-yl]-N'-phenyl hydrazine

Article abstract of DOI:10.1080/15421406.2011.590334

The title molecule, N-[4-(3-Methyl-3-phenyl-cyclobutyl)-thiazol-2-yl]-N'- phenyl hydrazine (C₂₀H₂₁N₃S), was prepared and characterized by elemental analysis, ¹H-NMR, ¹³C-NMR, FT-IR, UV-Visible (UV-Vis), and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2_1/c with a = 12.2960(5), b = 13.9565(5), c = 10.6356(5) A, and β= 99.106(3). Molecular geometries from X-ray experiment, vibrational frequencies, atomic charges distribution, dipole moments and total energies of the title compound and the dimer in the ground state have been calculated using the density functional theory method (RB3LYP) with 6-31G(d, p) and 6-311G(d, p) basis sets, and compared with the experimental data. Calculated results show that DFT at the RB3LYP/6-31G(d, p) and 6-311G(d, p) levels can well reproduce the structure of the title compound. To determine conformational flexibility, the molecular energy profile of the title compound was obtained by semi-empirical (RAM1) calculations with respect to the selected torsion angle, which was varied from-180 to +180 in steps of 10. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals, thermodynamic properties, and UV-Vis absorption spectra of the title compound were investigated using theoretical calculations. UV-Vis absorption spectra of the compound have been ascribed to their corresponding molecular structure and electrons orbital transitions. Copyright Taylor & Francis Group, LLC.

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Synthesis, Crystal Structure, and
Spectroscopic and Electronic Properties
of N-[4-(3-Methyl-3-Phenyl-Cyclobutyl)-
Thiazol-2-yl]-N′-Phenyl Hydrazine
H. Saraçoğlu a , F. Güntepe b , Ç. Yüksektepe c , N. Çalişkan b & A.
Cukurovali d
a Department of Middle Education, Educational Faculty , Ondokuz
Mayis University , 55139, Kurupelit, Samsun, Turkey
b Department of Physics, Faculty of Arts and Sciences , Ondokuz
Mayis University , 55139, Kurupelit, Samsun, Turkey
c Department of Physics, Faculty of Science , Çankırı Karatekin
University , 18100, Ballıca, Çankırı, Turkey
d Department of Chemistry, Faculty of Science , Firat University ,
23119, Elazig, Turkey
Published online: 07 Oct 2011.
To cite this article: H. Saraçoğlu , F. Güntepe , Ç. Yüksektepe , N. Çalişkan & A. Cukurovali (2011)
Synthesis, Crystal Structure, and Spectroscopic and Electronic Properties of N-[4-(3-Methyl-3-Phenyl-
Cyclobutyl)-Thiazol-2-yl]-N′-Phenyl Hydrazine, Molecular Crystals and Liquid Crystals, 548:1, 237-255,
DOI: 10.1080/15421406.2011.590334
To link to this article: http://dx.doi.org/10.1080/15421406.2011.590334
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Mol. Cryst. Liq. Cryst., Vol. 548: pp. 237–255, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.590334
Synthesis, Crystal Structure, and Spectroscopic and
Electronic Properties of N-[4-(3-Methyl-3-Phenyl-
Cyclobutyl)-Thiazol-2-yl]-Nꢀ-Phenyl
Hydrazine
1,∗
2
3
˘
¨
¨
H. SARAC¸ OGLU, F. GUNTEPE, C¸ . YUKSEKTEPE,
N. C¸ ALIS¸KAN,2 AND A. CUKUROVALI4
1Department of Middle Education, Educational Faculty, Ondokuz Mayis
University, 55139 Kurupelit, Samsun, Turkey
2Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayis
University, 55139 Kurupelit, Samsun, Turkey
3Department of Physics, Faculty of Science, C¸ ankırı Karatekin University, 18100
Ballıca, C¸ ankırı, Turkey
4Department of Chemistry, Faculty of Science, Firat University, 23119 Elazig,
Turkey
The title molecule, N-[4-(3-Methyl-3-phenyl-cyclobutyl)-thiazol-2-yl]-Nꢀ-phenyl hy-
drazine (C20H21N3S), was prepared and characterized by elemental analysis, 1H-NMR,
13C-NMR, FT-IR, UV-Visible (UV-Vis), and single-crystal X-ray diffraction. The com-
pound crystallizes in the monoclinic space group P21/c with a = 12.2960(5), b =
13.9565(5), c = 10.6356(5) Å, and β = 99.106(3)◦. Molecular geometries from X-ray
experiment, vibrational frequencies, atomic charges distribution, dipole moments and
total energies of the title compound and the dimer in the ground state have been cal-
culated using the density functional theory method (RB3LYP) with 6-31G(d, p) and
6-311G(d, p) basis sets, and compared with the experimental data. Calculated results
show that DFT at the RB3LYP/6-31G(d, p) and 6-311G(d, p) levels can well repro-
duce the structure of the title compound. To determine conformational flexibility, the
molecular energy profile of the title compound was obtained by semi-empirical (RAM1)
calculations with respect to the selected torsion angle, which was varied from −180◦
to +180◦ in steps of 10◦. In addition, the molecular electrostatic potential (MEP), fron-
tier molecular orbitals, thermodynamic properties, and UV-Vis absorption spectra of
the title compound were investigated using theoretical calculations. UV-Vis absorption
spectra of the compound have been ascribed to their corresponding molecular structure
and electrons orbital transitions.
Keywords DFT calculations; hydrazine derivative; IR spectra; X-ray structure deter-
mination
∗Address correspondence to Hanife Sarac¸og˘lu, Department of Middle Education, Educational
Faculty, Ondokuz Mayis University, TR-55139, Kurupelit, Samsun, Turkey. Fax: +90-362-4576078.
E-mail: hanifesa@omu.edu.tr
237

˘
H. Sarac¸oglu et al.
238
1. Introduction
Hydrazine is a highly reactive molecule used as a rocket propellant and an antioxidant in
water systems, and is used to produce plastic blowing agents. It is also a minor metabolite
of two important drugs, namely isoniazid, an antitubercular agent, and hydralazine, an
antihypertensive agent [1,2]. It has been said that hydrazine causes depletion of ATP
and GSH (glutathione) and the accumulation of triglycerides in the liver [3] as well as
neurological effects in experimental rats [4]. It is also a putative carcinogen [5]. The
mechanisms of hydrazine toxicity are not fully understood, although the accumulation of
triglycerides is in part due to the increased mobilization of fats from adipose tissues coupled
with a reduction in the transport of triglycerides out of the liver [6,7]. Hydrazine has been
reported to methylate DNA [8] and interfere in the urea cycle, with the result that citrulline
levels are raised in the livers of experimental animals [9,10]. Substituted hydrazines have
also found many scientific and commercial applications [11,12]. Thiazole itself and its
derivatives are of importance in biological systems as anti-inflammatory, analgesic agents
andinhibitors of lipoxygenaseactivities [13,14]. Onthe other hand, cyclobutaneaminoacids
in different structures were described as highly potent l-glutamate, N-methyl-D-aspartate
(NMDA) agonists, NMDA antagonists, and anticonvulsive drugs [15–17].
In recent years, density functional theory (DFT) has been a shooting star in theoretical
modeling. The development of ever better exchange-correlation functionals has made it
possible to calculate many molecular properties with accuracies comparable to those of
traditional correlated ab initio methods, with more favorable computational costs [18].
Literature surveys have revealed the high degree of accuracy of DFT methods in reproducing
the experimental values in terms of geometry, dipole moment, vibrational frequency, etc.
[19–25].
In the present paper, we report the synthesis, and structural and spectral characteriza-
tions of N-[4-(3-Methyl-3-phenyl-cyclobutyl)-thiazol-2-yl]-N’-phenyl hydrazine together
with DFT computational studies. The structural geometry, electronic charge distribution,
molecular electrostatic potential (MEP), and thermodynamic properties of the title com-
pound at the B3LYP/6-31G(d, p) level were studied. In addition, experimental and theoret-
ical results were compared.
2. Experiment
2.1. Synthesis of the Title Compound
Phenyl hydrazine and NH4SCN were purchased from Merck and used as received. 1-
methyl-1-phenyl-3-(2-chloro-1-oxoethyl) cyclobutane was synthesized according to the
literature procedure [26]. The compound was synthesized as shown in Scheme 1. To a
stirred solution of phenyl hydrazine (10 mmol) in 30 mL of ethanol, ammonium rhodanide
(10 mmol) in 20 mL of water was added. Subsequently, a solution of 1-methyl-1-phenyl-
3-(2-chloro-1-oxoethyl) cyclobutane (α-haloketone) (10 mmol) in ethanol (20 mL) was
added dropwise. After the addition of α-haloketone, the temperature was kept at 323–328
K for more than 2 h. After cooling to room temperature, the solution was then made
alkaline with an aqueous solution of NH3 (5%), and a light orange precipitate separated.
The precipitate was filtered off, washed with aqueous NH3 solution several times, and
dried in air. Suitable single crystals for crystal structure determination were obtained by
slow evaporation of its ethanol solution [yield: 84%, melting point: 464 K. Characteristic

Synthesis and Characterization of C20H21N3S
239
C
O
H3C
H2C
N
S
H3C
NH4SCN
Cl
NH NH C
NH
NH NH2
NH
NH2
NaHCO3
S
Scheme 1. Synthetic route for the synthesis of the target compound.
1H-NMR shifts (DMSO-d6, δ, ppm): 1.51 (s, 3H, CH3 in cyclobutane), 2.33–2.38 (m,
2H, CH2 in cyclobutane), 2.47–2.52 (m, 2H, CH2 in cyclobutane), 3.54 (q, j = 8.78
Hz, 1H, >C H in cyclobutane), 6.28 (s, 1H, = CH S), 6.70–6.75 (m, 3H, aromatics),
7.11–7.16 (m, 5H, aromatics), 7.28–7.31 (m, 2H, aromatics), 8.18 (s 1H, NH D2O
exchangeable), 9.28 (s, 1H, NH D2O exchangeable). Characteristic 13C-NMR shifts
(DMSO-d6, δ, ppm): 175.31, 157.10, 153.04, 149.23, 129.56, 128.85, 125.87, 125.27,
119.81, 112.91, 101.24, 40.79, 38.91, 31.29, 30.73. Elemental analysis for C20H21N3S
(335.47 gmol−1): Calculated: C: 71.61; H: 6.31; N: 12.53; S: 9.56. Found. C: 71.44; H:
6.37; N: 12.71; S: 9.88].
2.2. Measurement
IR spectrum was recorded on an ATI Unicam-Mattson 1000 FT-IR spectrometer using
1
KBr pellets. H-NMR and 13C-NMR spectra were obtained using a Bruker 300 MHz
spectrometer. The UV spectrum of the compound was performed on a Shimadzu UV-1700
spectrometer in a CHCl3 solvent.
2.3. X-Ray Crystallography
The data collection was performed at 296 K on a Stoe-IPDS-2 diffractometer equipped with
a graphite monochromated Mo-Kα radiation (λ = 0.71073 Å). The structure was solved
by direct methods using SHELXS-97 and refined by a full-matrix least-squares procedure
using the program SHELXL-97 [27]. All non-hydrogen atoms were easily found from the
difference Fourier map and refined anisotropically. All hydrogen atoms of carbons and
nitrogens were included using a riding model and refined isotropically with CH = 0.93 (for
phenyl groups), CH2 = 0.97, CH3 = 0.96, CH = 0.98, and NH = 0.86 Å [Uiso(H) = 1.2Ueq
(1.5 Ueq for methyl group)]. Details of the data collection conditions and the parameters of
the refinement process are given in Table 1.
3. DFT Calculations
The geometric optimization of the compound in the ground state (in vacuo) was performed
on a personal computer using experimental geometry as input, employing the GAUSSIAN-
03 program at DFT with the RB3LYP/6-31G(d, p) and RB3LYP/6-311G(d, p) levels [28].
Furthermore, the geometry of two molecules linked by N H . . . N hydrogen bonding
was taken from the experimental X-ray data and a full-geometry optimization on the
molecules, named as a dimer was carried out with the RB3LYP/6-31G(d, p) level. Then,

˘
240
H. Sarac¸oglu et al.
Table 1. Crystallographic data of the title compound
Empirical formula
C20H21N3S1
Mr
T (K)
335.46
296
Radiation, λ (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
β (Å)
V (Å3)
0.71073
Monoclinic
P21/c
12.2960(5)
13.9565(5)
10.6356(5)
99.106(3)
1802.16(13)
4
1.236
0.185
712
Z
Dc (g cm−3
µ/mm−1
F(000)
)
Crystal size (mm)
0.620 × 0.423 × 0.080
ꢀ range (◦)
1.7/27.5
Index range (h, k, l)
−15/15, −18/18, −13/13
27035
4132 (0.035)
3123
0.8392, 0.9332
4132/218
1.03
0.035
0.089
0.29 and −0.31
Reflections collected
Independent reflections (Rint)
Observed reflections[I > 2σ(I)]
Tmin, Tmax
Data/parameters
Goodness of fit on F2
Final R indices [I > 2σ(I)]
wR indices [I > 2σ(I)]
Largest diff. peak and hole (e. Å−3
)
we calculated vibrational frequencies for optimized molecular structures and scaled them
by 0.9806. To identify low-energy conformation, the selected degree of torsion angle,
T(C2 C3 C5 C10), was varied from −180◦ to +180◦ in steps of 10◦, and the molecular
energy profile was obtained at the semi-empirical RAM1 level.
The MEP was evaluated to research the reactive sites of the title compound using
the B3LYP/6-31G(d, p) level. On the basis of vibrational analysis, the thermodynamic
properties of the molecule at different temperatures were calculated. In addition, frontier
molecular orbital (FMO) analysis was carried out with the same level.
4. Results and Discussion
4.1. Description of the Crystal Structure
The title compound, an ORTEP-3 view of which is shown in Fig. 1, crystallizes in the
monoclinic space group P21/c with four molecules in the unit cell [29]. The asymmetric
unit in the crystal structure contains only one molecule.

Synthesis and Characterization of C20H21N3S
241
Figure 1. ORTEP drawing of the basic crystallographic unit, showing the atom numbering scheme.
Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small
spheres of arbitrary radii.
The title molecule is composed of a central thiazole ring, with a phenyl hydrazine
group connected to the 2-position of the ring and a (3-methyl-3-phenyl)cyclobutyl group in
the 4-position. The cyclobutane ring A (C1-C4), the thiazole ring B (S1/C14/N1/C12/C13),
the phenyl ring C (C5-C10), and the other phenyl ring D (C15-C20) are planar. The dihedral
angles between these planes are 46.95(9)◦, 36.64(10)◦, 37.78(11)◦, 80.17 (6)◦, 64.16 (6)◦,
and 58.06 (6)◦ for A/B, A/C, A/D, B/C, B/D, and C/D, respectively. In the thiazole ring,
the S1 C13 and S1 C14 bond lengths (Table 3) are shorter than the accepted value for an
S Csp2 single bond with 1.76 Å, resulting from the conjugation of the electrons of the S1
with atoms C13 and C14 [30].
In the cyclobutane ring A, the C4/C1/C2 plane forms a dihedral angle of 29.80 (20)◦
with the C2/C3/C4 plane. This value is significantly greater than those in the literatures:
23.5◦ [31], 18.92(15)◦ [32], and 19.26(17)◦ [33]. The geometry of the cyclobutane ring is
due to the steric effect of the methyl group.
The thiazole ring and the phenyl ring D are linked by a hydrazine group with
−126.90(18)◦ torsion angle. The molecules are linked in a head-to-head fashion by
N H . . . N hydrogen bonding (Table 2). In this hydrogen bonding, the atom N2 at
(x, y, z) acts as a donor to atom N1 at (–x, 1 – y, 1 – z). As a result, these in-
teractions formed a hydrogen-bonded dimer of graph set motif R22(8) ring at (m, n
+ 1/2, k + 1/2) (the other ring is formed between the molecule with symmetry
Table 2. Hydrogen bonds geometries of the crystal structure (Å, ◦)
D H . . . A
D H
H . . . A
D . . . A
D H . . . A
N2 H2 . . . N1i
0.86
0.93
0.96
2.14
2.70
2.91
2.975(2)
3.409(2)
3.768(3)
163
134
149
C13 H13 . . . Cg3ii
C11 H11B . . . Cg4i
Notes. Cg3 is the centroid of the C ring; Cg4 is the centroid of the D ring. Symmetry code: (i) −x,
1 – y, 1 – z; (ii): x, 1/2 – y, 1/2 + z.

˘
H. Sarac¸oglu et al.
242
Figure 2. (a) Diagram showing the hydrogen bond and π-ring interactions in the title compound.
Only those H atoms involved in the hydrogen bonding interactions are shown (symmetry codes: –x,
1 – y, 1 – z and x, 1/2 – y, 1/2 + z). (b) Partial packing diagram for the compound, showing the
N
H . . . N and C H . . . π interactions as broken lines. Hydrogen atoms not involved in hydrogen
bonding have been omitted (symmetry code: –x, 1 – y, 1 – z).
code (−x, y – 1/2, 1/2 – z) and the molecule with symmetry code (x, 1/2 – y, z
– 1/2) by same N H . . . N hydrogen bonding [34]. Also as a result, these interac-
tions formed a hydrogen-bonded dimer of graph set motif R22(8) ring at (m, n, k),
(where m, n, and k are integers). These dimers are linked by C H . . . π intermolecular

Synthesis and Characterization of C20H21N3S
243
Figure 3. Comparison of the molecular conformation of the compound as established from X-ray
study (black line) and solid-state DFT calculation with 6-31G(d, p) basis set (red line). Hydrogen
atoms have been omitted for clarity.
hydrogen bonds, as shown Fig. 2(b). The other C H . . . π intermolecular hydro-
gen bonds are also effective in the crystal packing, as shown in Fig. 2(a) and
Table 21.
4.2. Optimized Structure
DFT calculations were performed on the title compound at the RB3LYP/6-31G(d, p) and
RB3LYP/6-311G(d, p) levels. Some optimized geometric parameters are also listed in
Table 3. Comparing the theoretical values with the experimental ones indicates that all of
the optimized bond lengths are slightly larger than the experimental values, as the theoretical
calculations are performed for an isolated molecule in gaseous phase and the experimental
results are for a molecule in solid state. Thus, it was also compared with a dimeric structure
of the title compound using the DFT RB3LYP method with 6-31G(d, p) basis set. As a
result, using the root mean square error (RMSE) for evaluation, the dimeric structure best
predicts the bond distances, with an error of 0.016 Å, whereas the monomeric structure
best predicts the bond angles, with an error of 0.466◦.
The dihedral angles between optimized counterparts of the title compound are calcu-
lated at 45.57◦ (A/B), 36.61◦ (A/C), 41.84◦ (A/D), 75.09◦ (B/C), 74.29◦ (B/D), and 59.25◦
(C/D) for 6-31G(d, p), and at 30.91◦ (A/B), 45.08◦ (A/C), 68.49◦ (A/D), 75.21◦ (B/C),
74.29◦ (B/D), and 60.46◦ (C/D) for 6-311G(d, p). For the cyclobutane ring, the dihedral
angle between the C4/C1/C2 and the C2/C3/C4 plane is 29.80 (20)◦, whereas the dihedral
angle has been calculated at 7.35◦ for 6-31G(d, p), and at 24.58◦ for 6-311G(d, p).
4.3. Conformational Analysis
The X-ray structure of the title compound is compared with its DFT-optimized counterpart
(see Fig. 3), where conformational differences are shown between them. These differences
are given as RMSE of 0.402 Å for the RB3LYP/6-31G(d, p) level, and 0.385 Å for the
RB3LYP/6-311G(d, p) level. The calculated energy profile from RAM1 versus the torsion
angle C2 C3 C5 C10 is given in Fig. 4. The respective value of the selected degree
of torsion angle, T(C2 C3 C5 C10), is −54.2(2)◦ in the X-ray structure, whereas the
corresponding value in the optimized geometry is −41.2067◦ for B3LYP/6-31G(d, p),
1Crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Centre, CCDC No 735319. Copies of this information may be obtained free
of charge from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, United Kingdom (fax:
+44-1223-336033; E-mail: deposit@ccdc.cam.ac.uk; Website: www: http://www.ccdc.cam.ac.uk)

˘
H. Sarac¸oglu et al.
244
Table 3. Selected theoretical and experimental geometric parameters for the title compound
(bond lengths in Å, bond angles in degrees)
DFT (monomer)
6-31G(d, p) 6-311G(d, p)
DFT (dimer)
6-31G(d, p)
Experimental
Bond length (Å)
S1 C13
S1 C14
N1 C12
N1 C14
N2 C14
N2 N3
C3 C5
1.732(2)
1.7304(16)
1.3848(19)
1.306(2)
1.350(2)
1.393(2)
1.508(2)
1.531(3)
1.7522
1.7612
1.3905
1.2989
1.3825
1.3900
1.5174
1.5397
0.018
1.7521
1.7586
1.3879
1.2950
1.3813
1.3880
1.5161
1.5387
0.018
1.7536
1.7624
1.3935
1.3098
1.3650
1.3898
1.5178
1.5393
0.016
C3 C11
RMSEa
Max. differencea
Bond angle (◦)
C13 S1 C14
C14 N2 N3
N2 N3 C15
C12 N1 C14
C5 C3 C11
C11 C3 C2
RMSEa
0.032
0.031
0.032
87.84(8)
87.4204
117.4810
117.5519
110.4908
109.7759
111.7019
0.466
87.4280
117.8078
117.8605
110.8051
109.7818
111.6337
0.567
87.8792
117.0860
118.2124
111.0894
109.8481
111.7818
0.785
117.82(15)
116.94(15)
110.17(13)
109.11(15)
111.40(17)
Max. differencea
Dihedral angles (◦)
S1 C14 N2 N3
N1 C14 N2 N3
N2 N3 C15 C16
N2 N3 C15 C20
C14 N2 N3 C15
0.666
0.920
1.272
3.6(2)
−175.89(16)
15.5(3)
22.4445
−160.0475
24.5944
21.4196
−161.0163
23.2140
14.0326
−167.5148
19.9697
−166.17(17)
−157.7997
−159.3262
−162.6540
−126.90(18)
−140.2193
−137.9965
−130.7930
aRMSE and maximum differences between the bond lengths and the bond angles were computed
by the theoretical method and those obtained from X-ray diffraction.
−41.2709◦ for B3LYP /6-311G(d, p), and −40.6251◦ for the dimer. According to Fig. 4,
the minimum energy is located at −40◦, having energy of 126.447 kcal mol−1, and the
maximum energy is also located at 90◦, having energy of 128.719 kcal mol−1. The energy
difference between the most favorable and the most unfavorable conformer, which arises
from rotational potential barrier calculated with respect to the selected torsion angle, is
calculated as 2.272 kcal mol−1 when both selected degrees of torsion angle are considered.
The molecular energy can be divided into bonded and non-bonded contributions. The
bonded energy is considered to be independent of torsion angle changes and therefore
vanished when relative conformer energies were calculated. The non-bonded energy is
further separated into torsional steric and electrostatic terms. Hydrogen bond is an intense
electrostatic contribution [35]. Since there is no intramolecular hydrogen bond in the title
compound, the calculated structure is the most stable conformer, which is principally

Synthesis and Characterization of C20H21N3S
245
129.0
128.5
128.0
127.5
127.0
126.5
-200
-150
-100
-50
0
50
100
150
200
T(C2-C3-C5-C10)
Figure 4. Molecular energy profile of the optimized counterpart of the title compound versus selected
degrees of torsion angle.
determined by the non-bonded torsional energy and electrostatic energy terms affected by
packing of the molecules.
4.4. Mulliken Atomic Charges and Molecular Electrostatic Potential
The Mulliken atomic charges were calculated at the RB3LYP/6-31G(d, p) and RB3LYP/6-
311G(d, p) levels and are illustrated in Table 4. Atomic charge analysis revealed that the
negative charges on the nitrogen and carbon atoms (C11, C13) are significantly greater than
the other atoms, but the positive charges are expected to be localized on the protonated
N2 atom and carbon (C11, C13) atoms. However, the calculations show that the positive
charges on hydrogen atoms bound to the N2, C11, and C13 atoms are found to be greater
than those on other hydrogen atoms in the title compound. Thus, the positive charges may
be delocalized between N2, C11, C13, and hydrogen atoms.
The molecular electrostatic potential, V(r), at a given point r(x, y, z) in the vicinity
of a molecule, is defined in terms of the interaction energy between the electrical charge
generated from the molecule’s electrons and nuclei and a positive test charge (a proton)
located at r. For the system studied, the V(r) values were calculated as described previously
using the following equation [36]:
ꢀ
V (r) = ꢁZA/|RA − r| − ρ(rꢀ)/|rꢀ − r|d3rꢀ,
(1)
where ZA is the charge of nucleus A located at RA, ρ(rꢀ) is the electronic density function
of the molecule, and rꢀ is the dummy integration variable.
The MEP is related to the electronic density and is a very useful descriptor in under-
standing sites of electrophilic attack and nucleophilic reactions as well as hydrogen bonding

˘
246
H. Sarac¸oglu et al.
Table 4. Mulliken atomic charges of the title compound
Atom
B3LYP/6-31G(d, p)
B3LYP/6-311G(d, p)
S1
N1
N2
H2
0.221
−0.504
−0.409
0.272
0.228
−0.350
−0.308
0.228
N3
H3
−0.454
−0.353
0.261
0.222
C1
H1
−0.132
0.106
−0.190
0.124
C2
−0.184
−0.111
H2A
H2B
C3
0.099
0.112
0.093
0.111
−0.036
−0.166
0.096
0.104
0.116
−0.285
−0.087
0.112
C4
H4A
H4B
C5
C6
H6
0.115
−0.045
−0.063
0.088
−0.120
0.082
C7
H7
−0.088
0.082
−0.091
0.091
C8
H8
−0.086
−0.091
0.091
0.081
C9
H9
−0.088
0.082
−0.091
0.090
C10
H10
C11
H11A
H11B
H11C
C12
C13
H13
C14
C15
C16
H16
C17
H17
C18
H18
C19
H19
C20
H20
−0.120
−0.063
0.085
0.079
−0.304
0.105
0.099
0.107
0.305
−0.186
0.106
0.096
0.108
0.150
−0.356
−0.332
0.120
0.128
0.311
0.294
0.201
0.138
−0.097
−0.059
0.104
0.111
−0.096
0.087
−0.100
0.096
−0.089
−0.096
0.082
0.091
−0.090
0.086
−0.099
0.094
−0.131
−0.106
0.076
0.088

Synthesis and Characterization of C20H21N3S
247
Figure 5. Molecular electrostatic potential (MEP) map calculated at B3LYP/6-31G(d, p) level.
interactions [37–39]. The electrostatic potential V(r) is also well suited for analyzing pro-
cesses based on the “recognition” of one molecule by another, such as in drug–receptor and
enzyme–substrate interactions, because it is through their potentials that the two species
first “see” each other [40,41]. Being a real physical property, V(r) can be determined
experimentally by diffraction or computational methods [42].
MEP was calculated using the RB3LYP/6-31G(d,p) method. The red regions and blue
regions of the MEP represent negative and positive charges, respectively. As can be seen
in Fig. 5, this molecule has one possible site of electrophilic attack. The negative region
is localized on the unprotonated nitrogen atom of the thiazole ring, N1, with a minimum
value of −0.041 a.u. The positive regions are mainly over the other nitrogen atoms. The
positive V(r) values are 0.044 a.u. for N2 and 0.048 a.u. for N3. These regions predicate
to be intermolecular interactions, and Fig. 5 confirms the existence of an intermolecular
N H . . . N interaction between the protonated and the unprotonated N atoms of the title
compound.
4.5. Frontier Molecular Orbitals
The FMOs are important in determining properties such as molecular reactivity and the
ability of a molecule to absorb light. So, FMOs are very important for optical and electric
properties [43]. Energy levels of the HOMO – 2, HOMO – 1, HOMO (highest occupied
molecular orbital), LUMO (lowest occupied molecular orbital), LUMO + 1, and LUMO +
2 orbitals computed at the RB3LYP/6-31G(d, p) level for the title compound and the dimer
are shown in Figs. 6(a) and (b). The electron clouds of the HOMOs and HOMO – 1 orbitals
are localized on the rings of thiazole and benzene connected with a hydrazine bridge. The
HOMO of the monomer corresponds to both HOMO of the top molecule and HOMO – 1
of the bottom molecule of the dimer. The HOMO – 1 of the monomer corresponds to both
HOMO – 2 of the second molecule and HOMO – 3 of the first molecule of the dimer. The
LUMO of the monomer is similar to both LUMO of the bottom molecule and LUMO + 1
of the top molecule of the dimer. The LUMO + 1 of the monomer is similar to both LUMO
+ 2 of the first molecule and LUMO + 3 of the second molecule of the dimer. The HOMO

˘
H. Sarac¸oglu et al.
248
Figure 6. (a) Plots of the frontier molecular orbitals of the title compound. (b) Plots of the frontier
molecular orbitals of the dimer.

Synthesis and Characterization of C20H21N3S
249
Table 5. Calculated energy values and dipole moments of the title compound and the dimer
DFT/6-31G(d, p)
(monomer)
DFT/6-311G(d, p)
(monomer)
DFT/6-31G(d, p)
(dimer)
Orbital
HOMO (a.u.)
LUMO (a.u.)
ꢂ (a.u.) (eV)
Total energies (a.u.)
Dipole moments (D)
−0.2014
−0.0014
−0.2098
−0.0134
−0.1992
−0.0031
0.2000 (5.442)
−1337.2
0.1964 (5.344)
−1337.4
0.1961 (5.336)
−2674.4
1.8176
1.8066
0.2151
and LUMO energies, the energy gap, total energies, and dipole moments for the monomer
and the dimer have been calculated and are given in Table 5.
The HOMO–LUMO energy separation has been used as an indicator of kinetic stability
of the molecule [44,45]. A large HOMO–LUMO gap implies a high kinetic stability and
low chemical reactivity, because it is energetically unfavorable to add electrons to a high-
lying LUMO or to extract electrons from a low-lying HOMO [45]. The HOMO – 1 and
LUMO of the dimer correspond to the HOMO and LUMO of the bottom molecule of the
dimer. The HOMO–LUMO energy gap for the bottom molecule is 5.358 eV. The HOMO
and LUMO + 1 of the dimer correspond to the HOMO and LUMO of the top molecule of
the dimer. The HOMO–LUMO energy gap for the top molecule is 5.366 eV.
In the present work, the HOMO–LUMO energy gap in the dimer form (5.336 eV)
is found to be smaller than that in bottom and top molecules, which suggests that the
dimer form is likely to be more reactive than the monomer form. Besides, intermolecular
interactions have a significant influence in decreasing the HOMO–LUMO gaps in solids
[46,47].
4.6. Vibrational Spectra
FT-IR spectra were obtained on KBr disks using a Mattson 1000 FT-IR spectrometer
and are shown in Fig. 7. Harmonic vibrational frequencies of the title compound were
calculated at the RB3LYP/6-31G(d, p) and RB3LYP/6-311G(d, p) levels, and the obtained
frequencies were scaled by 0.9806. Using GaussView molecular visualization program [48],
the vibrational bands assignments have been made. In order to facilitate assignment of the
observed peaks, we have analyzed vibrational frequencies and compared our calculation of
the title compound with the experimental results, which are shown in Table 6.
The experimental N H asymmetric and symmetric stretchings and intra-planar bend-
ing modes were observed at 3300 cm−1, 3224 cm−1, and 1428 cm−1, respectively. As can
be easily seen, the experimental values of N−H stretching modes are smaller than the
calculated frequencies, because the title compound with the hydrazine group is involved
in hydrogen bonding. The experimental C N and C C stretch bands were observed at
1
1603 cm−1 and 1576 cm− , which have been calculated with 6-31G(d, p) and 6-311G(d,
1
p) at 1588–1553 cm−1 and 1576–1541 cm− , respectively. The other calculated vibrational
frequencies are presented in Table 6.
Comparing the calculated and the experimental data, we studied the relativity between
the calculations and the experiments and obtained linear function formulas y = 1.03469x
– 51.34278 (R2 = 0.99807) for B3LYP/6-31G(d, p), y = 1.02603x – 43.0309 (R2 =
0.99795) for B3LYP/6-311G(d, p). In these formulas, x and y are the experimental and

˘
H. Sarac¸oglu et al.
250
Table 6. Comparison of the observed and calculated vibrational spectra of the title
compound
Calculated (cm−1) (DFT/B3LYP)
Experimental
IR with
Scaled
freq.
Scaled
freq.
I(km
I (km
Assignments
KBr (cm−1
)
(6-31G(d, p)) mol−1) (6-311G(d, p)) mol−1
)
νas N H
νs N H
3300
3224
3179
3159
3128
3096
3082
3050
—
3437
3431
3147
3142
3130
3123
3109
3107
3066
3058
28.71
8.42
3431
3428
3130
3125
3113
3108
3093
3090
3047
3039
30.88
8.42
25.56
21.84
38.26
11.71
6.89
12.29
35.24
28.63
νs C H (aromatic)
νs C H (aromatic)
νas C H (aromatic)
νas C H (aromatic)
νas C H (aromatic)
νas C H (aromatic)
ν C H + νas C H2
ν C H + νas C H2 +
νas C H3
27.42
23.12
44.42
11.57
7.77
12.70
31.48
31.36
—
νas C H2 + νas C H3
—
3028
—
3052
—
13.64
—
45.44
7.32
32.93
15.15
25.42
135.41
—
—
νas C H3
3028
3026
2994
2985
2982
2961
1617
17.34
47.91
6.82
36.99
12.20
27.10
146.32
νas C H3
νs C H2
νs C H2
ν C H
3049
3009
3001
2995
2977
1633
—
2958
2924
2852
—
νs C H3
ν C C (aromatic)
+ γ NH
ν C C (aromatic)
ν C C (aromatic)
+ γ NH
—
—
1629
1621
10.79
21.80
1613
1608
11.52
25.51
ν C N
1603
1576
—
1546
1495
1588
1553
1512
1511
1502
284.81
20.96
52.83
13.37
45.67
1576
1541
1500
1499
1495
275.09
21.44
38.85
16.41
71.54
ν C C (aromatic)
γ CH (aromatic)
γ CH (aromatic)
γ CH (aromatic)
+ γ NH
α CH2
1443
—
—
1443
—
32.57
1447
1438
7.70
34.31
γ CH (aromatic)
+ γ NH
α NH
1428
—
1380
1371
—
1403
—
1370
1341
1323
96.64
—
16.35
7.67
18.04
1406
1384
1363
1329
1314
115.91
7.22
21.51
5.59
ω CH3
γ CH (aromatic)
γ CH (aromatic)
γ CH (aromatic)+ν
C N (aromatic)
+ ν C N
20.68
ν H3CC C (aromatic)
+ β CH2
1317
1304
47.41
1295
29.55

Synthesis and Characterization of C20H21N3S
251
Table 6. Comparison of the observed and calculated vibrational spectra of the title com-
pound (Continued)
Calculated (cm−1) (DFT/B3LYP)
Experimental
IR with
Scaled
freq.
Scaled
freq.
I(km
I (km
Assignments
KBr (cm−1
)
(6-31G(d, p)) mol−1) (6-311G(d, p)) mol−1
)
ν C N + ν C C
(aromatic)
1303
—
—
1292
30.33
ν C N (aromatic)
ν C N
1264
1248
—
1273
1257
1255
66.87
106.66
7.53
1266
1245
—
75.58
106.88
—
β CH2 + ν C CH3
(aromatic)
δ CH2 + γ CH
(aromatic)
ν HC C (aromatic)
+ γ CH (aromatic)
ν N N + γ CH
(aromatic)
—
—
—
1152
1148
1142
1087
9.44
10.40
13.02
5.54
1176
1154
1075
1155
1148
1091
16.10
12.59
7.05
δ CH3 + γ CH2 + γ CH
(aromatic)
α CH (aromatic)
α CH (aromatic)
α CH (aromatic)
δ CH2 + ν C N
(aromatic)
—
—
1019
—
1086
1035
1033
1016
5.23
7.78
5.79
7.94
1080
1030
1027
1013
6.89
9.54
7.10
7.94
δ CH (aromatic)
ν S CH
889
—
—
773
—
882
779
765
755
747
8.07
29.01
19.06
127.95
65.09
885
776
766
753
742
8.87
27.22
20.76
105.34
82.24
ω CH (aromatic)
ω CH (aromatic)
ω CH (aromatic)
+ ν C S
γ CH (aromatic)
ω CH (aromatic)
+ γ CH (aromatic)
ω CH (aromatic)
+ γ CH (aromatic)
ω CH (aromatic)
θ (aromatic)
752
—
706
703
26.69
22.47
—
704
—
43.02
717
—
—
702
28.01
—
—
—
692
639
549
519
496
694
679
655
641
594
546
514
—
8.89
13.97
41.16
120.05
33.70
10.72
16.51
—
695
678
652
637
585
545
512
509
22.37
15.90
14.63
137.84
30.91
16.36
17.51
8.35
ν C S
ν C S
α NH
ω CH (aromatic)
ω CH (aromatic)
ω CH (aromatic)
Vibrational modes: ν, stretching; β, bending; α, scissoring; γ , rocking; ω, wagging; δ, twisting;
θ, ring breathing; s, symmetric; as, asymmetric.

˘
252
H. Sarac¸oglu et al.
85
549
519
717
80
1075
1317
1371
1303
889
75
%
T
r
1019
639
a
n
s
m
i
t
t
a
n
c
70
65
60
55
496
773
1154
3028
1176
692
752
1546
3050
1248
1264
e
1495
3224
3179
1380
1428
3159
2341
2361
3300
1443
3128
2852
2924
2958
3096
3082
1576
1603
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber(cm-1
)
Figure 7. FT-IR spectrum of the title compound.
calculated frequencies, respectively. It can be observed from these values that the results of
the RB3LYP/6-31G(d, p) method has shown a better fit to the experimental ones than the
RB3LYP/6-311G(d, p) method in evaluating vibrational frequencies.
4.7. Thermodynamic Properties
On the basis of vibrational analysis at the RB3LYP/6-31G(d, p) level, the standard statis-
tical thermodynamic functions, viz., standard heat capacity (Cp0,m), standard entropy (Sm0 ),
and standard enthalpy (Hm0 ), for the title compound were obtained from the theoretical
frequencies and are listed in Table 7.
From Table 7, we can observe that the standard heat capacities, entropies, and enthalpies
are increasing with temperatures ranging from 100 K to 1000 K due to the fact that the
vibrational intensities of molecules increase with temperature. The correlation equations
between these thermodynamic properties and temperature T are as follows:
Cp0,m = −3.88416 + 0.34205T − 1.40204x10−4T 2 (R2 = 0.99901)
(2)
Sm0 = 67.69779 + 0.32838T − 6.16918x10−5T 2 (R2 = 0.99997)
(3)
(4)
Hm0 = −3.46405 + 0.03311T − 9.48337x10−5T 2 (R2 = 0.99944).
These thermodynamic properties are needed in the detailed modeling of reaction
mechanisms [49]. As we have no corresponding experimental results, we are not able to
make any comparison with these results. But these data are expected to be useful for future
research.

Synthesis and Characterization of C20H21N3S
253
Table 7. Thermodynamic properties of the title compound at different temperatures at the
B3LYP/6–31G(d, p) level
T (K)
Cp0,m (cal.mol−1.K−1
)
Sm0 (cal.mol−1.K−1
)
Hm0 (kcal.mol−1
)
100.00
200.00
298.15
300.00
400.00
500.00
600.00
700.00
800.00
900.00
1000.00
32.082
56.309
83.702
100.429
131.220
159.547
160.078
188.646
216.433
242.915
267.873
291.295
313.267
333.901
2.249
6.830
13.882
14.041
24.036
36.531
51.084
67.294
84.848
103.512
123.104
84.225
111.166
133.989
152.420
167.282
179.444
189.560
198.080
4.8. Electronic Absorption Spectra
The UV-Visible (UV-Vis) absorption spectra of the title compound were recorded in a
CHCl3 solution. The title compound exhibits absorption peaks in the UV-Visible region.
The absorption peaks are observed at 258, 242 nm for the title compound.
It is known that photon energy E is given by:
E = hc/λ,
(5)
where h is the Planck’s constant, c is the light velocity in vacuum, and λ is the wavelength
of light. For molecular maximum absorption spectrum, E can be replaced with molecular
orbital energy level difference (ꢂE); thus, the Equation (5) changes to [50]:
ꢂE = hc/λ.
(6)
Based on the photoabsorption theory, the FMOs of the title compound and the dimer
have been investigated using the RB3LYP/6-31G(d, p) calculations. Three-dimensional
plots of FMOs and the corresponding energy levels of the title compound and the dimer
are shown in Figs 6(a) and (b), respectively. Thus, the energy level difference (ꢂE) can
be obtained from a two-level electron interaction according to the principle that when
an electron drops from a higher level to a lower one, there is emission of a packet(s) of
electromagnetic radiation. Thus, electronic transfer (ET) peaks can be determined according
to Equation (6), which correspond to the experimental UV-Vis absorption peak [50]. The
theoretically ET peaks for the compound determined by the RB3LYP/6-31G(d, p) and
RB3LYP/6-311G(d, p) basis sets are at 228, 225 and 232, 226 nm, which correspond to
the UV-Vis spectral absorption peaks, and the corresponding electronic transfers happened
between HOMO and LUMO and between HOMO and LUMO + 1, respectively. The smaller
theoretical absorption wavelengths of the compound have slight blue shifts compared with
the corresponding experimental ones.
5. Conclusions
In this work, the compound N-[4-(3-Methyl-3-phenyl-cyclobutyl)-thiazol-2-yl]-N’-phenyl
1
hydrazine has been characterized by elemental analysis, H-NMR, 13C-NMR, X-ray

˘
H. Sarac¸oglu et al.
254
analysis, FT-IR, and UV-Vis techniques. The X-ray structure is found to be very slightly
different from its optimized counterparts, and the crystal structure is stabilized by a
N H . . . N-type hydrogen bond between the protonated and the unprotonated N atoms
and by C H . . . π interactions. The DFT RB3LYP/6-31G(d, p) and RB3LYP/6-311G(d,
p) levels calculations were performed to further study the molecular structure, vibrational
spectra, and electronic absorption spectra of the title compound. The results show that the
optimized bond lengths are slightly longer than the experimental values, and the optimized
bond angles are some different from the experimental ones. Vibrational assignments of
the compound were ascribed to their structural vibrations, which show that the theoretical
harmonic frequencies are in generally good agreement with their observed spectral features.
The energy gap value of the title compound is between 5.336 eV and 5.442 eV. This result
indicates that the title structure is quite stable. The correlations between the thermodynamic
properties Cp0,m, Sm0 , Hm0 , and temperature T were also obtained. These values can be used
to calculate the other thermodynamic energies according to relationships of thermody-
namic functions and to estimate directions of chemical reactions. As a result, all of these
calculations will provide helpful information for further studies on the title compound.
Acknowledgment
The authors wish to acknowledge the Faculty of Arts and Sciences, Ondokuz Mayis Uni-
versity, Turkey, for the use of the STOE IPDS-II diffractometer (purchased under grant
F.279 of the University Research Fund).
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