Synthesis, molecular and crystal structure analysis of 2-bromo-4-chloro-6- {[4-(3-methyl-3-phenyl-cyclobutyl)-thiazol-2-yl]-hydrazonomethyl}-phenol by experimental methods and theoretical calculations

Article abstract of DOI:10.1016/j.molstruc.2012.05.002

A novel hydrazone derivative 2-bromo-4-chloro-6-{[4-(3-methyl-3-phenyl- cyclobutyl)-thiazol-2-yl]-hydrazonomethyl}-phenol was synthesized and characterized by IR, UV-Vis spectroscopy and X-ray single crystal diffraction. The compound crystallizes in monoclinic space group P2₁/c with a = 8.0862(3) ?, b = 7.6168(1) ?, c = 37.3168(12) ? and β = 91.186(1)°. In addition, the molecular geometry and vibrational frequencies of the title compound in ground state have been calculated by using density functional theory (DFT) at B3LYP level with 6-31G and 6-31G(d, p) basis sets. The geometrical parameters of the title compound obtained from XRD studies are in good agreement with the calculated values. The analysis of IR spectrum supported by DFT calculations was particularly devoted to the manifestations of hydrogen bonding in the ν_str(NH) and ν_str(OH) vibrations. To determine the conformational flexibility for a selected torsion angle τ(C6C1C7N1) one-dimensional potential energy scan was performed using AM1 in the full range of 0-360°increasing of 10°. UV-Vis absorption spectrum of the compound has been compared to theoretical spectrum (vertical excitations) computed by time dependent density functional theory (TD-DFT). Besides frontier molecular orbitals and molecular electrostatic potential map analysis were investigated by theoretical calculations.

Full text of DOI:10.1016/j.molstruc.2012.05.002

Journal of Molecular Structure 1022 (2012) 204–210
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, molecular and crystal structure analysis of
2-bromo-4-chloro-6-{[4-(3-methyl-3-phenyl-cyclobutyl)-thiazol-2-yl]-
hydrazonomethyl}-phenol by experimental methods and theoretical calculations
b
c
d
e
Feyizan Güntepe a, , Hanife Saraçog˘lu , Nezihe Çalısßkan , Çig˘dem Yüksektepe , Alaaddin Cukurovali
⇑
a Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayis University, Samsun, Turkey
b Department of Physics Education, Faculty of Education, Ondokuz Mayis University, Samsun, Turkey
c Department of Physics, Faculty of Sciences, Gazi University, Ankara, Turkey
d Department of Physics, Faculty of Science, Cankiri Karatekin University, Cankiri, Turkey
e Department of Chemistry, Faculty of Science, Firat University, Elazig, Turkey
h i g h l i g h t s
"
"
"
We investigate molecular and crystal structure of the new hydrazone derivative.
Crystal structure is stabilized by NAHÁ Á ÁO, OAHÁ Á ÁO and CAHÁ Á ÁO type hydrogen bonds.
The calculated frequencies for mstr(OAH) and mstr(NAH) higher the experimental ones.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 September 2011
Received in revised form 1 May 2012
Accepted 1 May 2012
Available online 14 May 2012
A
novel hydrazone derivative 2-bromo-4-chloro-6-{[4-(3-methyl-3-phenyl-cyclobutyl)-thiazol-2-yl]-
hydrazonomethyl}-phenol was synthesized and characterized by IR, UV–Vis spectroscopy and X-ray sin-
gle crystal diffraction. The compound crystallizes in monoclinic space group P21/c with a = 8.0862(3) Å,
b = 7.6168(1) Å, c = 37.3168(12) Å and b = 91.186(1)°. In addition, the molecular geometry and vibrational
frequencies of the title compound in ground state have been calculated by using density functional the-
ory (DFT) at B3LYP level with 6-31G and 6-31G(d,p) basis sets. The geometrical parameters of the title
compound obtained from XRD studies are in good agreement with the calculated values. The analysis
of IR spectrum supported by DFT calculations was particularly devoted to the manifestations of hydrogen
Keywords:
Hydrazone
Crystal structure
IR spectroscopy
DFT calculation
bonding in the
selected torsion angle
mstr(NAH) and
mstr(OAH) vibrations. To determine the conformational flexibility for a
s
(C6AC1AC7AN1) one-dimensional potential energy scan was performed using
AM1 in the full range of 0–360° increasing of 10°. UV–Vis absorption spectrum of the compound has been
compared to theoretical spectrum (vertical excitations) computed by time dependent density functional
theory (TD-DFT). Besides frontier molecular orbitals and molecular electrostatic potential map analysis
were investigated by theoretical calculations.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
forming drug carrier system employing suitable carrier proteins
[8]. They are also employed as extracting agents in spectrophoto-
Hydrazones are an important class of compounds due to their
diverse applications. Hydrazones and their metal complexes pos-
sess pronounced biological and pharmaceutical activities as antitu-
mor [1–4], antimicrobial [5], antituberculosis [6] and antimalarial
agents [7]. Hydrazones play an important role in improving the
antitumor selectivity and toxicity profile of antitumor agents by
metric determination of some ions [9–11] and spectrophotometric
determination of some species in pharmaceutical formulations
[12], as well as waste water treatment [13]. Metal complex of
hydrazones have found applications in various chemical processes
like non-linear optics and sensors [14] and have been used in the
separation and concentration of palladium and platinum in road
dust [15]. Hydrazones have found wide applications in synthetic
chemistry [16], to be used as indicators. Hydrazones have been uti-
lized for the determination of carbonyl compounds [17,18]. The
⇑
Corresponding author. Fax: +90 362 4576081.
E-mail address: feyizanguntepe@gmail.com (F. Güntepe).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.05.002

F. Güntepe et al. / Journal of Molecular Structure 1022 (2012) 204–210
205
Table 1
hydrazones have been used for different purposes such as herbi-
Crystallographic data for title compound.
cides, insecticides, nematocides and plant growth regulators [19].
The hydrazones are also important for their use as plasticizers
and stabilizers for polymers [20], polymerization initiators and
antioxidant [21].
Empirical formula
Molecular weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C21H19BrClN3OSÁH2O
476.81
296
0.71073 Mo K
Monoclinic
P21/c
a radiation
The title compound 2-bromo-4-chloro-6-{[4-(3-methyl-
3-phenyl-cyclobutyl)-thiazol-2-yl]-hydrazonomethyl}-phenol is a
kind of hydrazone derivatives. Beside of its possible pharmacolog-
ical relevance this molecule is also an interesting model for studies
vibrational spectrum in hydrogen bonding system. Vibrational
spectrum provides the most commonly used criteria for the pres-
ence and properties of hydrogen bonds. The most significant spec-
tral changes resulting from H-bond formation occur in the IR
spectrum in particular in the region of XAH stretching bands.
These are the decrease in frequency in the NAH stretching mode,
increase of its intensity, broadening of the bands and appearance
of a complex fine structure [22]. The mechanisms of these phe-
nomena are subject of many theoretical studies. On the other hand
an alternative computational methods have long been carried out
for equilibrium structure properties of molecular system such as
geometry and vibrational frequency. Computational methods are
at present widely used for simulating IR spectrum [1]. Such simu-
lations are indispensable tools to perform normal mode analysis so
that modern vibrational spectroscopy is unimaginable without
involving them. In this paper, we present the result of the detailed
investigation of synthesis and structural characterization of title
compound using XRD, IR and UV–Vis spectroscopy and quantum
chemical methods. The geometric parameters and vibrational fre-
quencies of the title compound in ground state were calculated
DFT/B3LYP method with 6-31G and 6-31G(d,p) basis sets. The
aim of the study is an analysis and discussion of results for one rep-
resentative member of this hydrazone family. These discussions
are valuable for providing insight into molecular structure and
chemical behavior.
Unit cell dimensions (Å,°)
a = 8.0862(3)
b = 7.6168(1)
c = 37.3168(12)
= 90
b = 91.186(1)
= 90
a
c
Volume (Å3)
2297.89(12)
4
2.757
2.02
Integration (X-RED32)
0.2210, 0.4396
Z
Calculated density (mg mÀ3
)
l
(mmÀ1
)
Absorption correction
Tmin, Tmax
Crystal size (mm)
Diffractometer/measurement
Index ranges (h,k,l)
0.60 Â 0.46 Â 0.18
STOE IPDS 2/rotation (
x scan)
h = À9 ? 9, k = À9 ? 9, l = À45 ? 45
H
Range (°)
2.2–25.6
Reflections collected
Independent reflections
Observed reflections [I > 2
Rint
21.535
4326
3381
0.054
r
(I)]
Refinement method
Full-matrix least-squares on F2
Goodness-of-fit on F2
1.04
0.042
0.110
0.36, À0.51
0.0008(4)
777381
R (I > 2
wR (I > 2
r
)
r
)
D
qmax
,
D
qmin
Extinction coefficient
CCDC
at 323–328 K for 2 h more. After cooling to the room temperature
the solution was then made alkaline with an aqueous solution of
NH3 (5%), and a light olive green precipitate separated. The precip-
itate 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: 77%, melting point: 449 K.
2. Experimental
2.1. General remarks
Melting point was determined by Gallencamp melting point
apparatus. FT-IR spectrum was recorded on KBr pellet with a ATI
Unicam-Mattson 1000 FT-infrared spectrometer 4000–400 cmÀ1
range. The UV spectrum of the compound was performed on a
Schimadzu UV-1700 spectrometer in CHCl3 solvent. All reagents
were commercially obtained and used without any further
purification.
2.3. X-ray crystal structure determination
Data collection was carried out on a Stoe-IPDS-2 diffractometer
equipped with
a graphite monochromated Mo Ka radiation
(k = 0.71073 Å) at 293 K. The structure was solved by direct meth-
ods using SHELXS-97 [23] implemented in the WinGX software
system [24] and refined by full-matrix least-squares procedure
using SHELXL-97 [25]. All non-hydrogen atoms were easily found
from the difference Fourier map and refined anisotropically. All
hydrogen atoms were included using a riding model and refined
isotropically with CAH = 0.93–0.97 Å and NAH = 0.86 Å. Uiso(H) =
1.2Ueq(C,N), Uiso(H) = 1.5Ueq(for methyl group). Data collection,
X-AREA [26]; cell refinement X-AREA; data reduction, X-RED32
[26] The molecular structure plots were prepared by using the
2.2. Synthesis
The title compound was synthesized as shown in Scheme 1 by
the following procedure. To a stirred solution of 3-bromo-5-chloro
salicylaldehyde (10 mmol) in 30 mL of ethanol, thiosemicarbazide
(10 mmol) was added portions. Subsequently, a solution of phena-
cyl chloride (10 mmol) in 20 mL of ethanol was added dropwise.
After the addition of the
a-haloketone, the temperature was kept
Scheme 1. The synthesis pathway of the title compound.

206
F. Güntepe et al. / Journal of Molecular Structure 1022 (2012) 204–210
ORTEP III [27]. Crystallographic data, details of the data collection
and structure refinements are listed in Table 1.
hydrazone is reported as 1.449 Å [36] and electron diffraction
NAN bond length of tetramethylhydrazone is reported at 1.401 Å
[37] while for the title compound the N1AN2 bond length of
hydrazone (C7@N1AN2) fragment is 1.367(3) Å which is some-
where between the length of Nsp2ANsp2 single bond (1.401 Å)
[38] and N@N double bond (1.25 Å) [1]. The X-ray studies have
showed that the AOH group is in an ortho-position to the hydra-
zone linkage which enable O1AH1Á Á ÁN1 intramolecular hydrogen
bond producing a graph set motif of S(6) [39]. In the crystal lattice
the hydrogen bonds established via water molecule. The atom O(2)
of water at (x,y,z) acts as a bifurcated hydrogen bond donor to
atoms N(3) at (x,y,z) and O(1) at (1 À x,2 À y,Àz), with inversion
symmetry, via H2WA and H2WB respectively. Besides of this the
atom O(2) of water at (x,y,z) acts as a bifurcated hydrogen bond
acceptor to atoms N(2) and C(7) at (1 À x,1 À y,Àz). Therefore mol-
ecules are packed by intermolecular hydrogen bonds in zigzag
arrangement parallel to c axis in the crystal structure as seen from
Fig. 2. The details of hydrogen bonds are given in Table 2.
2.4. Computational methods
All the calculations are performed for the title compound by
using Gaussian 03 program package on a personal computer [28].
The molecular structure of the title compound in the ground state
(in vacou) was optimized using DFT/B3LYP [29,30] method with
following standard basis sets: 6-31G, valance double zeta functions
and 6-31G(d,p), valance double zeta plus polarization functions of
d and p type. For modeling the initial guess of title compound was
obtained from the X-ray refinement data. The harmonic vibrational
frequencies analysis was performed at the same level of theory. No
scale factor was used in the calculated frequencies. The molecular
electrostatic potential map and frontier molecular orbital surfaces
are visualized by GausView Molecular Visualization program [31].
3. Result and discussion
3.1. Crystallographic results
The title compound which is shown in Fig. 1 as an Ortep III view,
crystallizes in monoclinic space group P21/c with four molecules in
the unit cell. The asymmetric unit in the crystal structure contains
only one molecule with a crystalline water.
The title molecule is composed of a central thiazole ring with 2-
bromo-4-chloro-phenol group connected to the 2-position of the
ring via hydrazone group and 3-methyl-3-phenyl-cyclobutyl in
the 4-position. The thiazole ring A (S1/C10/C9/N3/C8), phenol ring
B (C1AC6) and phenyl ring C (C16AC21) are each approximately
planar. The dihedral angle between these rings are 1.6(2)°,
77.6(2)° and 78.8(2)° for A/B, A/C and B/C respectively. The steric
interaction between the substituent groups on the cyclobutane
ring D (C11AC14) means that this ring derivates significantly from
planarity. In this case the C14/C13/C12 plane forms a dihedral an-
gle of 23.3(2)° with the C12/C11/C14 plane in cyclobutane ring.
Similar puckering of cyclobutane ring has been reported 23.5(2)°
[32] and 24.09(12)° [33]. In thiazole ring there are two different
CAN bond distances, viz. C8@N3 and C9AN3. The C8@N3 double
bond length is 1.307(3) Å and C9AN3 single bond is 1.381(4) Å.
The C9@C10 bond length is 1.343(4) Å, characterizing a C@C dou-
ble bond. The S1AC8 and S1AC10 bond distances are shorter than
the accepted value for an SACsp2 single bond with 1.76 Å [34]
resulting from the conjugation of the electrons of atom S1 with
atoms C8 and C10 [35]. The experimental NAN bond length of
Fig. 1. ORTEP drawing of the basic crystallographic unit of the title compound,
showing the atom-numbering scheme. Displacement ellipsoids are drawn at the
50% probability level and all H atoms are shown as small spheres of arbitrary radii.
Fig. 2. A partial packing diagram of the title compound, hydrogen bonding
interactions have been shown as broken lines.

F. Güntepe et al. / Journal of Molecular Structure 1022 (2012) 204–210
207
Table 2
Hydrogen bonding geometries for the title compound.
70
DAHÁ Á ÁA
DAH (Å)
HÁ Á ÁA (Å)
DÁ Á ÁA (Å)
DAHÁ Á ÁA (°)
O1AH1Á Á ÁN1
0.82
1.90
2.620(3)
2.840(4)
2.953(4)
2.790(3)
3.206(4)
147
O2AH2WAÁ Á ÁN3
O2AH2WBÁ Á ÁO1i
N2AH2AÁ Á ÁO2ii
C7AH7Á Á ÁO2ii
0.82(3)
0.84(3)
0.86
2.07(3)
2.14(3)
1.98
157(3)
163(3)
158
60
50
40
30
0.93
2.44
140
Symmetry code: (i) 1 À x, 2 À y, Àz ; (ii) 1 À x, 1 À y, Àz.
Table 3
Selected experimental and optimized geometric parameters of the title compound.
Parameter
Experimental
DFT/B3LYP
6-31G
6-31G(d,p)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers
Bond lengths (Å)
N1AC7
N1AN2
N2AC8
N3AC8
N3AC9
C9AC10
S1AC8
1.284(4)
1.367(3)
1.343(4)
1.307(3)
1.381(4)
1.343(4)
1.728(3)
1.725(3)
1.540(4)
1.546(5)
1.549(5)
1.536(5)
1.350(3)
1.488(4)
1.512(5)
1.354(6)
1.320(8)
1.381(7)
1.352(6)
1.389(6)
1.312(7)
1.305
1.363
1.363
1.317
1.406
1.360
1.817
1.818
1.568
1.573
1.575
1.557
1.339
1.495
1.519
1.405
1.399
1.399
1.405
1.399
1.399
1.295
1.350
1.367
1.311
1.389
1.362
1.755
1.753
1.559
1.564
1.565
1.550
1.340
1.496
1.517
1.401
1.395
1.395
1.401
1.395
1.395
Fig. 3. The experimental FT-IR spectrum of the title compound.
to X-ray study dihedral angles between the A, B, C planes are calcu-
lated as 2.52° (A/B), 76.69° (A/C), 76.75° (B/C) for 6-31G basis set
and 3.19° (A/B) 74.24° (A/C), 74.24° (B/C) for 6-31G(d,p) basis set.
The dihedral angle between the C14/C13/C12 and the C12/C11/
C14 planes (puckering of the cyclobutane ring) is calculated as
23.46° for 6-31G basis set and 24.79° for 6-31G(d,p) basis set. Se-
lected bond lengths, bond angles and torsion angles of optimized
geometry are listed in Table 3 with experimental ones.
As can be seen in Table 3 most of the calculated bond lengths
are slightly longer than the experimental ones except N1AN2
and O1AC6 which are shorter. The largest difference between
experimental and calculated bond length is 0.093 Å which is calcu-
lated with 6-31G basis set for S1AC10. The largest difference be-
tween experimental and calculated bond angle is 2.41° which is
calculated with B3LYP/6-31G(d,p) for C8AN2AN1. It is well known
that for an accurate description at least double zeta quality basis
augmented with a set of polarization functions set is needed.
Therefore a somewhat better geometry description is expected
with 6-31G(d,p) basis set. Using the root mean square (RMS) error
for consideration it is found that the B3LYP/6-31G(d,p) calculation
provide the lowest RMS value of 0.032 Å and 0.99° for bond lengths
and bond angles respectively. Consequently the B3LYP calculation
with 6-31G(d,p) basis set predicts the best geometry when com-
pared the calculation with 6-31G basis set.
S1AC10
C11AC12
C12AC13
C13AC14
C14AC11
O1AC6
C9AC11
C16AC13
C16AC17
C18AC21
C17AC18
C16AC19
C19AC20
C20AC21
RMSEa
0.045
0.093
0.032
0.083
Max. differencea
Bond angles (°)
C10AS1AC8
C9AN3AC8
C8AN2AN1
N2AN1AC7
N1AC7AC1
C1AC6AO1
C11AC12AC13
C13AC14AC11
C14AC11AC12
C12AC13AC14
88.32(14)
110.9(2)
118.6(2)
117.2(2)
121.5(3)
121.8(2)
89.2(3)
89.2(3)
88.8(2)
88.1(2)
86.32
112.51
120.88
119.11
121.52
121.99
88.94
89.27
88.85
88.06
87.85
110.97
121.01
118.42
122.13
122.55
88.86
89.16
88.65
87.89
3.3. IR spectroscopy
RMSEa
1.32
2.28
0.99
2.41
FT-IR spectrum are obtained in KBr disks using a Mattson 1000
FT-IR spectrometer, and shown in Fig. 3. Based on optimized geom-
etries harmonic vibrational frequencies were calculated by using
same method and basis sets as. The calculated frequencies were
not scaled. Frequency calculations at the same level of theory re-
vealed no imaginary frequencies indicating that an optimal geom-
etry at these levels of approximation was found for the title
compound. By using Gauss View molecular visualization program
[31], the vibrational band assignments have been made. The exper-
imental and calculated frequencies are given in Table 4 with their
assignments. It is well known that the calculated ‘non-scale’ har-
monic frequencies could significantly overestimate experimental
values due to lack of electron correlation, insufficient basis sets
and anharmonicity and noted that the experimental results belong
to solid phase and theoretical calculations belong to gaseous phase.
Thus there is a reasonable agreement between experimental and
calculated frequencies, except for the OH and NH stretching bands.
Max. differencea
Torsion angles (°)
N2AN1AC7AC1
C7AN1AN2AC8
N1AN2AC8AN3
C7AC1AC6AO1
C9AN3AC8AN2
N1AN2AC8AS1
179.1(2)
179.3(2)
À176.9(2)
0.9(4)
178.8(2)
3.2(4)
179.61
177.96
À179.37
0.16
179.51
0.45
179.38
177.34
À179.20
0.19
179.67
0.75
RMSEa
1.82
2.77
1.80
2.47
Max. differencea
a
RMSE and maximum differences between the bond lengths and the bond angles
computed by the theoretical method and those obtained from X-ray diffraction.
3.2. Optimized structures
In order to verify the accuracy of used theoretical model the
investigated molecule is fully optimized in the gas phase and opti-
mized geometry compared with experimental geometry. According
The
mstr(OAH) vibration of crystalline water is observed at
3563 cmÀ1 and is calculated 3755 cmÀ1 and 3857 cmÀ1 for 6-31G

208
F. Güntepe et al. / Journal of Molecular Structure 1022 (2012) 204–210
Table 4
Comparison of the observed and calculated vibrational spectra (cmÀ1) of the title
compound.
Assignments
Experimental DFT/B3LYP
6-
6-
31G
31G(d,p)
masym–str (OH) water
msym–str (OH) water
mstr (OH) phenol
mstr (CH) thiazole
mstr (NH) hydrazone
mstr (CH) aromatic
msym–str (CH) aromatic
masym–str (CH) aromatic
masym–str (CH2)
masym–str (CH3)
msym–str (CH2)
msym–str (CH3)
msci (OH) water
3563
–
3755
3253
3215
3323
3253
3231
3222
3200
3135
3111
3073
3035
1642
1697
1667
3857
3528
3443
3283
3254
3210
3205
3171
3121
3108
3063
3036
1689
1671
1640
3320
3218
3159
3070
3055
3022
2945
2930
2858
2848
–
Fig. 4. Molecular electrostatic potential map (in a.u.) of the title compound
computed with the B3LYP/6-31G(d,p) level.
mstr (C@N) hydrazone + mbend (NH)
mstr (C@N) thiazole + mbend (NH)
hydrazone
1654
1619
mstr (CC) aromatic
mstr (C@C) thiazole
msci (CH2)
mbend (OH) phenol
msci (CH3)
1596
1564
1444
1420
1346
1298
1221
1168
1105
859
1638
1601
1512
1519
1453
1288
1297
1222
1173
879
1637
1587
1507
1434
1419
1331
1311
1187
1162
860
Lumo+1: -0.36898 eV
mwag CH2)
mbend (CH) aromatic
mtwist (CH2)
mbend-out of plane (CH) aromatic
mrock (CH2)
789
875
852
mbend-out of plane (OH) phenol
mbend-out of plane (NH)
mbend-out of plane (CC)
mbend (CASAC)
762
720
700
658
772
830
797
–
759
783
761
–
Lumo: -1.87950 eV
Vibrational modes: str; stretching, bend; bending, sci; scissoring, rock; rocking,
wag; wagging, twist; twisting, sym; symmetric, asym; asymmetric.
and 6-31G(d,p) respectively. The band observed at 3320 cmÀ1 is
Homo: -5.63633 eV
attributed to the absorption of the mstr(OAH) vibration of phenol
which is calculated 3215 cmÀ1 and 3443 cmÀ1 for 6-31G and 6-
31G(d,p) respectively. The NH stretching band is observed at
3159 cmÀ1 which is calculated 3253 cmÀ1 and 3254 cmÀ1 for 6-
31G and 6-31G(d,p) respectively. Such differences between exper-
imental and calculated frequencies for
mstr(OAH) and mstr(NAH)
bands could be expected for such modes in a medium strong
hydrogen bond [40]. Since our main interest of IR study is the char-
acterization of intramolecular and intermolecular hydrogen bonds
so no elaborate normal mode analysis was performed and only the
approximate description of selected modes is given in Table 4.
Homo-1: -6.22873 eV
3.4. Molecular electrostatic potential
Homo-2: -6.52779 eV
The molecular electrostatic potential (MEP) is related to the
electronic density and is a very useful descriptor for determining
sites of chemical reactivity of the molecule for electrophilic attack
and nucleophilic reactions as well as hydrogen-bonding interac-
tions [41–43]. To predict reactive sites for electrophilic and nucle-
ophilic attack for the title molecule, MEP was calculated at the
B3LYP/6-31G(d,p) optimized geometry. The negative (red) regions
of MEP were related to electrophilic reactivity and the positive
Homo-4: -6.94140 eV
Fig. 5. Molecular orbital surfaces and energy levels given in parentheses for the
HOMO-4, HOMO-2, HOMO-1, HOMO, LUMO, LUMO + 1 of the title compound
computed with the B3LYP/6-31G(d,p) level.
(blue1
be seen from Fig. 4 there are two possible sites on the title com-
pound for electrophilic attack with maximum value of
) regions to nucleophilic reactivity shown in Fig. 4. It can
a
À0.0641 a.u. However, positive (blue) regions are localized on
hydrogen atoms of water molecule and C7 atom with a maximum
value of 0.0575 a.u. These results provide information concerning
the region where the compound can interact intermolecularly.
1
For interpretation of color in Figs. 1, 2, 4, 5 and 8, the reader is referred to the web
version of this article.

F. Güntepe et al. / Journal of Molecular Structure 1022 (2012) 204–210
209
36.4
0.5
36.2
36.0
35.8
35.6
35.4
35.2
35.0
34.8
0.4
0.3
0.2
0.1
0.0
2.0
1.5
1.0
0.5
0.0
290 300 310 320 330 340 350 360 370
λ (nm)
-50
0
50
100
150
200
250
300
350
400
100
200
300
400
500
600
700
800
τ
(C6-C1-C7-N1)
Wavelength (nm)
Fig. 7. Energy profile of the optimized counterpart of the title compound for the
rotation about (C6AC1AC7AN1) torsion angle.
Fig. 6. The experimental absorbtion spectrum of the title compound in CHCl3
solution. Inset: calculated absorbtion spectra of title compound. The excited states
are shown as vertical bars with high equal to oscillator strength.
s
do not evaluate the spin–orbit splitting; the values are averaged.
Here, in this paper the objective is to evaluate the electronic struc-
ture by direct electronic excitations and only singlet–singlet tran-
sitions considered. In addition the role of solvent effect of
solution is not included in the theoretical calculation.
3.5. Frontier molecular orbital analysis and absorption spectra
Analyses of frontier molecular orbital provide helpful informa-
tion for studies on electrical and optical properties as well as in
UV–Vis spectrum and chemical reactions [44]. Fig. 5 shows surface
and energy levels of the HOMO-4, HOMO-2, HOMO-1, HOMO,
LUMO and LUMO + 1 orbitals which are computed at the B3LYP/
6-31G(d,p) for the title compound. The calculations indicate that
the compound has 126 occupied MOs. From Fig. 5 both the highest
occupied molecular orbitals (HOMOs) and the lowest unoccupied
molecular orbitals (LUMOs) mainly delocalized on the thiazole
and phenol rings connected with hydrazone linkage. The HOMOs
3.6. Conformational analysis
In order to determine the preferential position of phenol ring
with respect to hydrazone fragment a preliminary search of low
energy structures was performed using AM1 computations as a
function of the selected degrees of torsional freedom
(C6AC1AC7AN1). The calculated energy profile with respect to
rotations about the selected torsion angle (C6AC1AC7AN1) is gi-
s
are mostly
p-bonding type orbitals and the LUMOs are p-antibond-
s
ing type orbitals.
ven in Fig. 7 and the optimized geometries of the most favorable
and unfavorable conformations are illustrated in Fig. 8a and b
respectively. The respective value of the selected degree of torsion
The absorption spectrum of the title compound was recorded in
CHCl3 at room temperature and theoretical absorption spectrum is
predicted by using TD-DFT method based on B3LYP/6-31G(d,p) le-
vel optimized structure. A comparison of calculated (vertical exci-
tations) and experimental electronic spectrum is reported in Fig. 6
and all of the data are listed in Table 5. The visible absorption spec-
trum of the title compound appears as highly intense absorbtion
angle s(C6AC1AC7AN1) is 0.85(40)° in X-ray structure, whereas
the corresponding value in optimized geometry is À0.36° for
B3LYP/6-31G and À0.57° for B3LYP/6-31G(d,p). As can be seen
from Fig. 7 the minimum energy domain is located at 310° having
energy of 34.827 kcal molÀ1, the maximum energy is also located
at 190° having energy of 36.279 kcal molÀ1. Energy difference be-
tween the most favorable and unfavorable conformer, which arises
from rotational potential barrier calculated with respect to the se-
lected torsion angle, is calculated as 1.452 kcal molÀ1 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 inde-
pendent of torsional angle changes and therefore vanished when
relative conformer energies are calculated. The non-bonded energy
bands at 376 nm and 252 nm which are mainly due to p–
pà tran-
sition. As seen from Fig. 6 three bands appeared in the calculated
spectrum having some differences compared with the correspond-
ing experimental ones. The reasons for the discrepancy between
the experimental values and theoretical predictions may be as fol-
lows: TD-DFT approach is based on the random-phase approxima-
tion method (RPA) [45–47] which provides an alternative to
computationally demanding multireference configuration interac-
tion methods in the study of excited states. TD-DFT calculations
Table 5
Experimental and theoretical electronic absorption spectra values.
Excitation
Electronic transition
Oscillator strength (f)
0.4713
ktheo (nm)
367.42
kexp (nm)
1
2
126(HOMO) ? 127(LUMO)
376
122(HOMO-4) ? 128(LUMO + 1)
124(HOMO-2) ? 127(LUMO)
125(HOMO-1) ? 127(LUMO)
126(HOMO) ? 128(LUMO + 1)
0.0410
320.19
3
124(HOMO-2) ? 127(LUMO)
125(HOMO-1) ? 127(LUMO)
0.0001
298.41
252

210
F. Güntepe et al. / Journal of Molecular Structure 1022 (2012) 204–210
bridge Crystallographic Data Centre (CCDC), 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 (0)1223 336033; email:
deposit@ccdc.cam.ac.uk].
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CCDC 777381 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cam-