Synthesis, spectroscopic characterization and quantum chemical computational studies on 1-acetyl-3,5-di(4-methylphenyl)-1H-pyrazole

Article abstract of DOI:10.1016/j.molstruc.2012.06.013

The pyrazole compound 1-acetyl-3,5-di(4-methylphenyl)-1H-pyrazole, (C ₁₉H₁₈N₂O), was characterized by X-ray single crystal diffraction technique, IR-NMR spectroscopy and quantum chemical computational methods as both experimental and theoretically. The compound crystallizes in the monoclinic space group C 2/c with a = 32.5334 (1) ?, b = 5.8060 (1) ?, c = 23.6519 (8) ?, β = 134.572 (2)°, and Z = 8. The molecular geometry was also optimized using the Hartree-Fock (HF) and density functional theory (DFT/B3LYP) methods with the 6-311G(d,p) basis set and compared with the experimental data. To determine conformational flexibility, molecular energy profile of the tittle compound was obtained by semi-empirical (AM1) with respect to selected degree of torsional freedom, which was varied from -180° to +180° in steps 10°. From the optimized geometry of the molecule, vibrational frequencies, gauge-independent atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values, molecular electrostatic potential (MEP) distribution, non-linear optical properties, frontier molecular orbitals (FMOs) of the title compound have been calculated in the ground state theoretically. The theoretical result showed good agreement with the experimental values.

Full text of DOI:10.1016/j.molstruc.2012.06.013

Journal of Molecular Structure 1027 (2012) 133–139
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic characterization and quantum chemical computational
studies on 1-acetyl-3,5-di(4-methylphenyl)-1H-pyrazole
a,
a
b
c
a
⇑
_
_
Ersin Inkaya , Muharrem Dinçer , Elif Korkusuz , Ismail Yıldırım , Orhan Büyükgüngör
a Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
b Erciyes University, Kayseri Vocational College, 38039 Kayseri, Turkey
c Department of Chemistry, Faculty of Arts and Sciences, Erciyes University, 38039 Kayseri, Turkey
h i g h l i g h t s
"
"
"
Pyrazole, X-ray single crystal diffraction.
Density functional theory (DFT) and Hartree–Fock (HF).
Molecular electrostatic potential (MEP) distribution and non-linear optical properties (NLO).
a r t i c l e i n f o
a b s t r a c t
Article history:
The pyrazole compound 1-acetyl-3,5-di(4-methylphenyl)-1H-pyrazole, (C19H18N2O), was characterized by
X-ray single crystal diffraction technique, IR–NMR spectroscopy and quantum chemical computational
methods as both experimental and theoretically. The compound crystallizes in the monoclinic space group
C 2/c with a = 32.5334 (1) Å, b = 5.8060 (1) Å, c = 23.6519 (8) Å, b = 134.572 (2)°, and Z = 8. The molecular
geometry was also optimized using the Hartree–Fock (HF) and density functional theory (DFT/B3LYP)
methods with the 6-311G(d,p) basis set and compared with the experimental data. To determine conforma-
tional flexibility, molecular energy profile of the tittle compound was obtained by semi-empirical (AM1)
with respect to selected degree of torsional freedom, which was varied from À180° to +180° in steps 10°.
From the optimized geometry of the molecule, vibrational frequencies, gauge-independent atomic orbital
(GIAO) 1H and 13C NMR chemical shift values, molecular electrostatic potential (MEP) distribution, non-lin-
ear optical properties, frontier molecular orbitals (FMOs) of the title compound have been calculated in the
ground state theoretically. The theoretical result showed good agreement with the experimental values
Ó 2012 Elsevier B.V. All rights reserved.
Received 10 February 2012
Received in revised form 1 June 2012
Accepted 2 June 2012
Available online 15 June 2012
Keywords:
X-ray structure determination
IR and NMR spectroscopy
DFT/HF calculations
Molecular electrostatic potential (MEP)
Non-linear optical properties
1. Introduction
worthwhile to design and synthesize new pyrazole derivatives. In
this paper, 1-acetyl-3,5-di(4-methylphenyl)-1H-pyrazole was like
Many natural products have the pyrazole unit as the core struc-
ture [1]. Pyrazole derivatives exhibit important biological properties
such as antitumor [2], anticoagulant [3], anti-hyperglycemic, anal-
gesic, anti-inflammatory, anti-pyretic, antibacterial, hypoglycemic
and sedative-hypnotic activity [4–6]. These derivatives have
attracted significant attention because of the application in drug
development [7]. Particularly, arylpyrazolesare important in medic-
inal and pesticidal chemistry [8]; a number of herbicides with pyra-
zole moieties have been commercialized [9]. Recent literature
shows that, some arylpyrazoles were reported to have non-nucleo-
side HIV-1 reverse transcriptase inhibitory activity [10,11]. They are
also useful intermediates for many industrial products [12–14]. Due
to the importance of the pyrazole nucleus, we believed it
prepared chloride by the reaction of 3,5-bis(4-methyphenyl)-1H-
pyrazole with acetyl chloride and characterized by elemental analy-
sis, FT-IR, 1H, 13C-NMR and elemental analysis, and the product is
completely original. The title compound is a novel compound syn-
thesized firstly in our laboratories by us.
Investigations into the structural stability of these compounds
using both experimental techniques and theoretical methods have
been of interest for many years. With recent advances in computer
hardware and software, it is possible to correctly describe the phys-
ico-chemical properties of molecules from first principles using
various computational techniques [15]. In recent years, density
functional theory (DFT) has been the shooting star in theoretical
modeling. The development of ever better exchange–correlation
functionals has made it possible to calculate many molecular prop-
erties with accuracies comparable to those of traditional correlated
ab initio methods, at more favorable computational costs [16].
⇑
Corresponding author. Tel.: +90 362 3121919/5256; fax: +90 362 4576081.
E-mail address: ersin.inkaya@oposta.omu.edu.tr (E. Inkaya).
_
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.06.013

_
134
E. Inkaya et al. / Journal of Molecular Structure 1027 (2012) 133–139
Literature surveys have revealed the high degree of accuracy of DFT
methods in reproducing the experimental values in terms of geom-
etry, dipole moment, vibrational frequency, etc. [17–22].
with Bruker Avance III 400 MHz spectrometers and the chemical
shifts were recorded in ppm units. After completion of the reac-
tions, solvents were evaporated with rotary evaporator (Heildolph
4001 G1). All other reagents were purchased from Merck, Fluka, Al-
drich and used without further purification.
In this study, we present results of a detailed investigation of
the synthesis and structural characterization of the title compound
using single crystal X-ray diffraction, IR and NMR spectroscopy and
quantum chemical methods. The geometrical parameters, funda-
mental frequencies and GIAO 1H and 13C NMR chemical shift
values of the title compound in the ground state have been calcu-
lated by using the HF/6-311G(d,p) and B3LYP/6-311G(d,p) meth-
ods. This calculation is valuable for providing insight into
molecular parameters and the vibrational spectrum and NMR spec-
trum. The aim of this work is to explore the molecular dynamics
and the structural parameters that govern the chemical behavior,
and to compare predictions made from theory with experimental
observations.
2.1.3. Crystallography
The single-crystal X-ray data were collected on a STOE IPDS II
image plate diffractometer at 296 K. Graphite-monochromated Mo
Ka radiation (k = 0.71073 Å) and the w-scan technique were used.
The structure was solved by direct methods using SHELXS-97 [26]
and refined through the full-matrix least-squares method using
SHELXL-97 [27], implemented in the WinGX [28] program suite.
Non-hydrogen atoms were refined with anisotropic displacement
parameters. All H atoms were located in a difference Fourier map
and were refined isotropically. Data collection: Stoe X-AREA [29],
cell refinement: Stoe X-AREA [29], data reduction: Stoe X-RED
[29]. Details of the data collection conditions and the parameters
of the refinement process are given in Table 1. The general-purpose
crystallographic tool PLATON [30] was used for the structure analy-
sis and presentation of the results.
2. Experimental and theoretical methods
2.1. Experimental
2.1.1. Synthesis
2.2. Theoretical
The starting material (3,5-di(4-methylphenyl)-1H-pyrazole) was
prepared from the reaction of 1,3-di(4-methylbenzoyl)methane
[23–25] with hydrazine monohydrate in ethanol by us. An equimo-
lar mixture of 3,5-di(4-methylphenyl)-1H-pyrazole (0.5 g,
1.7 mmol) and acetyl chloride (0.15 g, 1.7 mmol) was refluxed in xy-
lene for 3 h by adding 2–3 drops pyridine. The solvent was evapo-
rated, then the oily residue was treated with diethyl ether and the
formed crude product was recrystallized from methanol. (Yield:
The molecular structure of the compound in the ground state (in
vacuo) was optimized using Hartree–Fock (HF) and density func-
tional theory (DFT/B3LYP) [31,32] methods with the 6-311G(d,p)
basis set. For modeling, the initial guess of the compound was first
obtained from the X-ray coordinates. Then, vibrational frequencies
for the optimized molecular structure were calculated with DFT/
B3LYP method and then scaled by 0.9669 [33]. The geometry of
the compound, together with that of Tetramethylsilane (TMS), is
fully optimized. 1H and 13C NMR chemical shifts were calculated
within GIAO approach [34,35] applying the same methods and the
basis set as used for geometry optimization. The predicted 1H and
13C NMR chemical shifts were derived from the equation
85%; M.p. 85 °C). Analysis calculated for
g/mol): C 78.59, H 6.25, N 9.65%; found: C 78.63, H 6.24, N 9.64%
(Scheme.1).
C19H18N2O (290.36
2.1.2. General remarks
Melting points were measured on an Electro thermal 9200
apparatus and are uncorrected. Microanalysis for C and H was per-
formed using a Leco-932 CHNS-O elemental analyzer. The IR
spectra of the compound were recorded in the range of 400–
4000 cmÀ1 region using a Shimadzu FT-IR 8400 model spectrome-
ter with KBr pellets. The 1H and 13C NMR spectra were measured
d = R0
À
R, where d is the chemical shift, R is the absolute shielding
Table 1
Crystal data and structure refinement parameters for the title compound.
CCDC deposition no.
Color/shape
838,067
Colorless/Prism
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C19H18N2O
290.35
296
0.71073 Mo K
Monoclinic
C2/c
a
Unit cell parameters
a, b, c (Å)
32.5334 (1), 5.8060 (1), 23.6519 (8)
a
, b,
c
(°)
90, 134.572 (2), 90
3182.56 (16)
8
1.212
0.08
Volume (Å3)
Z
Dcalc (g/cm3)
l
(mmÀ1
)
F(000)
1232
Crystal size (mm3)
Diffractometer/measurement
method
0.62 Â 0.55 Â 0.42
STOE IPDS 2/
x scan
Index ranges
À40 6 h 6 40, À7 6 k 6 7,
À29 6 l 6 29
h range for data collection (°)
Reflections collected
Independent/observed reflections
Rint
1.7 6 h 6 26.5
23079
3304/2752
0.050
Refinement method
Full-matrix least-squares on F2
3304/0/199
Data/restraints/parameters
Goodness-of-fit on F2
1.08
R indices [I > 2
R indices (all data)
qmin (e/Å3)
r
(I)]
R1 = 0.0552, wR2 = 0.1672
R1 = 0.0650, wR2 = 0.1756
0.29, À0.26
D
qmax, D
Scheme 1. The formation of the title compound.

_
E. Inkaya et al. / Journal of Molecular Structure 1027 (2012) 133–139
135
Table 2
and R0 is the absolute shielding of the standard (TMS), whose values
Experimental and optimized geometrical parameters of the title compound.
are 32.46 and 196.41 ppm for HF, and 31.99 and 184.79 ppm for
B3LYP methods with the 6-311G(d,p) basis set, respectively. All
the calculations were performed without specifying any symmetry
for the title molecule by using Gauss View molecular visualization
program [36] and Gaussian 03 program package [37]. The effect of
solvent on the theoretical NMR parameters was included using the
default model IEF-PCM (Integral-Equation-Formalism Polarizable
Continuum Model) [38] provided by Gaussian 03. Chloroform was
used as solvent. In order to describe conformational flexibility of
the title molecule, the selected torsion angles T (C4AC5AC8AN1)
and T (C14AC13AC10AN2), was varied from À180° to À180° in
every 10° and the molecular energy profile as a function of the se-
lected torsional degree of freedom is obtained by performing single
point calculations on the calculated potential energy surface, and
the molecular energy profile was obtained at the AM1 level of the-
ory. For the calculation of MEP [39,40], the same level theory
B3LYP/6-311G(d,p), was used.
Parameters
Experimental
Calculated
HF/6-311G(d,p)
B3LYP/6-311G(d,p)
Bond lengths (Å)
N1AN2
N1AC3
N1AC11
N2AC1
O1AC11
C10AC7
C7AC6
C6AC5
C5AC4
C4AC9
C9AC8
1.373 (2)
1.381 (2)
1.418 (3)
1.320 (2)
1.203 (2)
1.507 (3)
1.368 (3)
1.387 (3)
1.379 (3)
1.383 (3)
1.374 (3)
1.485 (3)
1.507 (3)
1.350
1.375
1.404
1.289
1.182
1.509
1.382
1.388
1.383
1.392
1.376
1.506
1.510
0.06
1.366
1.394
1.424
1.322
1.204
1.508
1.395
1.392
1.399
1.401
1.386
1.509
1.508
0.01
C11AC12
C16AC19
RMSDa
Bond angles (°)
N2AN1AC3
N2AN1AC11
C1AN2AN1
N2AC1AC13
N2AC1AC2
O1AC11AN1
O1AC11AC12
N1AC11AC12
C17AC16AC19
C6AC7AC10
C4AC5AC6
C5AC4AC9
C9AC4AC3
C3AC2AC1
RMSDa
111.42 (15)
118.70 (15)
105.36 (14)
120.28 (16)
110.63 (16)
119.58 (18)
124.4 (2)
116.06 (16)
121.13 (19)
121.4 (2)
111.08
118.89
106.80
121.61
110.40
121.08
123.35
115.55
121.47
121.56
120.70
118.58
122.12
105.77
0.09
115.55
118.49
106.05
121.18
110.48
120.99
123.93
115.06
120.84
121.39
120.86
118.20
122.93
106.64
1.10
3. Results and discussion
3.1. Description of the crystal structure
The title compound, a DIAMOND [41] view of which is shown in
Fig. 1, is a crystallizing in the monoclinic space group C 21/c with
eight molecules in unit cell. The asymmetric unit of the compound
consists of one independent molecule. The atomic coordinates and
thermal parameters for the compound can be obtained from
Supplementary material. The selected bond lengths and angles
are listed in Table 2. The tittle molecule is composed of a central
pyrazole ring, with an acetyl group connected to the 1-position
of the ring and two 4-methylphenyl groups in the 3,5-positions.
In the crystal structure, two (4-methylphenyl) groups are cis posi-
tion with respect to the pyrazole ring.
120.0 (2)
118.17 (18)
121.51 (18)
106.82 (18)
Dihedral angles (°)
C11AN1AN2AC1
N1AN2AC1AC2
C9AC4AC3AN1
N2AN1AC11AO1
173.39(17)
À0.5 (2)
174.65
À0.19
173.97
À0.25
61.5(3)
58.23
51.16
À172.09(19)
À177.34
À177.08
The pyrazole ring is planar with a maximum deviation of
À0.0025 (12) Å for atom C1. All bond lengths and bond angles for
phenyl rings are within a normal range typical for such compounds.
There are two obviously different CAN bond distances in the pyra-
zole ring, viz. C1@N2 and C3AN1. The C1@N2 bond length is all
longer than and C3AN1 bond length is all shorter than those found
in similar structures [C@N 1.381 (2)–1.320 (2) Å, CAN 1.482(2)–
1.515(9) Å] [42], resulting from the conjugation of the electrons of
atom N with atom C. In this relation, this result is consistent with
the respect to different pyrazole derivatives. The C11AO1 bond
length is indicative of a significant double bond character. The dihe-
dral angle between pyrazole ring with the phenyl rings (C4AC9)
and (C13AC18) are 61.35 (1)° and 10.80 (2)°, respectively. Addition-
ally, the dihedral angle between pyrazole ring with the acetyl group
is 7.73 (4)°.
a
RMSD (root mean of square deviation) computed using theoretical methods and
those obtained from X-ray diffraction.
The crystal structure does not exhibit intermolecular, XAHÁ Á ÁCg
(p-ring) (edge-to-face) or p–p stacking (face-to-face) interactions.
There are, however, one CAHÁ Á ÁN intramolecular interaction, de-
tails of which is given in Table 3. An intramolecular C12AHÁ Á ÁN2
contact leads to the formation of a five-membered ring with
graph-set descriptor S(5) [43]. The packing is further stabilized
by Van der Waals forces.
3.2. Optimized structures
The molecular structure of the title compound was also studied
theoretically. The starting coordinates were those obtained from
the X-ray structure determination. Some selected geometric
parameters experimentally obtained and theoretically calculated
by using the Hartree–Fock (HF) and density functional theory
(DFT/B3LYP) methods with the 6-311G(d,p) basis set are listed in
Table 2.
As can be seen in Table 2, most of the optimized bond lengths
are slightly longer than the experimental values and the optimized
bond angles are slightly different from the experimental values due
to the difference of the studied molecular states. The isolated mol-
ecule is considered in gas phase in the theoretical calculation,
while the experimental results are related to the molecular packing
in solid state. According to X-ray study, the dihedral angle between
the pyrazole ring with the phenyl rings (C4AC9) and (C13AC18)
are 61.35 (1)° and 10.80 (2)°, whereas the dihedral angles have
been calculated 56.72° and 11.94(2)° for HF and 49.30° and 4.55°
DFT/B3LYP methods with 6-311G(d,p) level. The calculated DAH,
Fig. 1. A view of the title compound showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 40% probability level and H atoms are
shown as small spheres of arbitrary radii. Hydrogen bonds are indicated by broken
lines.

_
136
E. Inkaya et al. / Journal of Molecular Structure 1027 (2012) 133–139
Table 3
well known that the calculated HF and DFT ‘raw’ or ‘non-scale’ har-
Hydrogen bonding geometry for the title compound.
monic frequencies can significantly overestimate experimental
values due to lack of electron correlation insufficient basis sets
and anharmonicity. Harmonic vibrational frequencies of the title
compound were calculated by using density functional theory
(DFT/B3LYP) methods with the 6-311G(d,p) basis set. Frequency
calculations revealed no imaginary frequencies, indicating that an
optimal geometry at these levels of approximation was found for
the title compound. We compared our calculation for the title com-
pound with the experimental results. Theoretical and experimental
results of the tittle compound are shown in Table 4. The vibrational
bands assignments have been made by using Gauss View [36]
molecular visualization program. The agreement between the
experimental and calculated frequencies is satisfactory in general.
In the higher frequency region, almost all of the vibrations be-
long to CH3 and ring CH stretching vibrations. The CH and CH3
symmetrical and asymmetrical stretching vibrations are observed
at 2849–3030 cmÀ1 range and theoretically these frequencies have
been calculated at 2922–3099 cmÀ1 region for DFT/B3LYP method
with 6-311G(d,p) level.
DAHÁ Á ÁA
C12AH12AÁ Á ÁN2
HF/6-311G(d,p)
C12AH12AÁ Á ÁN2
B3LYP/6-311G(d,p)
C12AH12AÁ Á ÁN2
DAH (Å)
HÁ Á ÁA (Å)
2.22
DÁ Á ÁA (Å)
2.738 (3)
DAHÁ Á ÁA (°)
113
0.96
1.08
1.09
2.66
2.65
2.71
2.72
81
81.76
Note: The atom numbering according to Fig. 1 used.
HÁ Á ÁA, DÁ Á ÁA and DAHÁ Á ÁA values for this interactions are 1.08 Å,
2.66 Å, 2.71 Å and 81.00° for HF and 1.09 Å, 2.65 Å, 2.72 Å and
81.76° for B3LYP methods with 6-311G (d,p), respectively.
The root mean square deviation (RMSD) values for bond lengths
are 0.06 and 0.01 for HF and DFT/B3LYP methods, respectively.
Consequently, DFT correlates a little better for the geometrical
parameters than the HF method.
3.3. Vibrational spectra
In the pyrazole ring, the C@N and C@C stretching modes were
found at 1585 cmÀ1 as experimentally. These modes were calcu-
lated at 1566 cmÀ1 for same method. The tittle compound shows
The FT-IR spectrum of the title compound were recorded in the
4000–400 cmÀ1 region using KBr pellets on a Shimadzu FT-IR 8400
model spectrometer and given with theoretical ones in Fig. 2. It is
a strong band at 1742 cmÀ1 which is assigned to
mC@O stretching.
Fig. 2. (a) Experimental and (b) theoretical FT-IR spectrum of the title compound.

_
E. Inkaya et al. / Journal of Molecular Structure 1027 (2012) 133–139
137
Table 4
were observed to be in the range between 7.82 and 2.40 ppm,
and so the proper assignments need careful interpretation. In the
1H NMR spectra of the compound, the chemical shift values of
CAH3 protons were observed to be 2.40(H10), 2.83(H12) and
2.40(H19) ppm, respectively. These signals have been calculated
as 2.50, 2.64 and 2.44 ppm for HF, and 2.46, 2.69 and 2.42 ppm
for B3LYP methods with the 6-311G(d,p) level, respectively. The
CH hydrogen of the pyrazole ring appears at 6.81 ppm, and these
value is determined computationally at 6.80 ppm for HF/6-
311G(d,p) and 6.89 ppm for B3LYP/6-311G(d,p).
Comparison of the observed and calculated vibrational spectra of the title compound.
Assignments
Experimental IR with KBr
Calculated
B3LYP/6-311G(d,p)
(cmÀ1
)
Scal.
Freq.
I (km/
mol)
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m
sCAH (R)
sCAH (R)
sCAH (R)
sCAH (R)
asCAH (R)
asCAH (R)
asCAH (R)
asCAH (R)
asCAH3
asCAH3
asCAH3
sCAH3
sCAH3
3030
3099
3093
3077
3076
3055
3054
3053
–
3052
2999
3000
2999
2922
1748
1602
1566
1540
–
6
3
–
–
–
3010
–
13
11
19
18
24
–
14
18
19
21
35
350
16
5
We have calculated 13C chemicalshift values(with respect to TMS)
of 174.69–21.53 ppm for HF and 177.23–23.79 ppm for B3LYP meth-
ods with the 6-311G(d,p) level, however, the experimental results
were observed to be 170.61–21.42 ppm. In the 13C NMR spectrum,
the C10, C2 and C11 signals were observed at 21.42, 109.61 and
170.61 ppm, that have been calculated at 21.61, 110.83 and
174.69 ppm for HF, and at 23.79, 115.12 and 177.23 ppm for B3LYP
methods with the 6-311G(d,p) level, respectively.
The root mean square deviation (RMSD) values are 1.296 and
1.011 for HF and DFT/B3LYP methods, respectively. Consequently,
DFT correlates a little better for the chemical shifts than the HF
method.
–
–
2928
–
–
2849
–
1742
1610
1585
–
1585
1501
–
C@O
CAC
C@C +
m
C@N
CAH
h (r)
28
–
q
m
CAH
CAN +
q
1489
1450
1446
1435
1433
1430
72
44
11
11
6
d CAH3
d CAH3
d CAH3
d CAH3
–
–
–
–
3.5. Molecular electrostatic potential
x
CAH3
CAH
+
q
19
The molecular electrostatic potential (MEP) is related to the
electronic density and is a very useful descriptor in understanding
sites for electrophilic attack and nucleophilic reactions as well as
hydrogen-bonding interactions [44–46]. The electrostatic potential
V(r) are also well suited for analyzing processes based on the ‘‘rec-
ognition’’ of one molecule by another, as in drug–receptor, and
enzyme–substrate interactions, because it is through their poten-
tials that the two species first ‘‘see’’ each other [47,48]. Being a real
physical property V(r) can be determined experimentally by dif-
fraction or by computational methods [49].
To predict reactive sites for electrophilic and nucleophilic attack
for the title molecule, MEP was calculated by applying the DFT/
B3LYP) method and 6-311G(d,p) basis set for the optimized geom-
etry. The negative (red) regions of MEP were related to electro-
philic reactivity and the positive (blue) regions to nucleophilic
reactivity shown in Fig. S1 (see Supplementary materials).
As can be seen in from the figure, there are two possible sites on
the title compound for electrophilic attack. The negative regions
are mainly over the O1 atom. The maximum values of negative
and positive regions are À0.053 and 0.022 a.u., respectively. For
the title compound, negative regions were calculated: the MEP va-
lue around O1. These results provide information concerning the
region where the compound may have intra- or intermolecular
interaction.
x
x
CAH3
CAH3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1420
1415
1266
1201
1193
–
1175
1150
1106
1089
1057
922
10
4
193
32
3
m
CAN +
x
CAH3
q
q
CAH (R)
CAH (R)
b CANAN (r)
–
m
NAN (r)
CAH
CAH
CAH3
CAH (r)
14
33
19
10
7
116
16
67
q
q
q
q
bdeformation (r)
x
x
CAH (R)
CAH (R)
812
800
Vibrational modes: m, stretching; d, scissoring; q, rocking; x, wagging; b, in-plane
bending; h, ring breathing. Abbreviations: s, symmetric; as, asymmetric; R, benzene
ring; r, pyrazole ring.
The stretching mC@O vibration gives rise to a band in the experi-
mental infrared spectrum at 1742 cmÀ1, and the calculated value
is predicted to be 6 cmÀ1 higher at 1748 cmÀ1 for B3LYP/6-
311G(d,p). The CAC and CAN stretching vibrations are found to
be 1601 and 1489 cmÀ1 for the same level, respectively. The other
calculated vibrational frequencies can be seen in Table 4.
3.4. NMR spectra
3.6. Frontier molecular orbitals
The characterization of the compound was further enhanced by
the use of 1H and 13C NMR spectroscopy. The 1H and 13C NMR spec-
tra of the compound recorded in chloroform (CDCl3) solution at
298 K are shown in Fig. 3. In addition, theoretical 1H and 13C
NMR chemical shift values of the compound have been computed
using the same methods and the basis set for the two optimized
geometries. The results of these calculations are tabulated in Table
5 together with the experimental values. Since experimental 1H
chemical shift values were not available for individual hydrogen
atoms of CH3 groups, we have presented the average of the com-
puted values for these hydrogen atoms.
The frontier molecular orbitals play an important role in the
electric and optical properties, as well as in UV–Vis spectra and
chemical reactions [50]. Fig. S2 (see Supplementary materials)
shows the distributions and energy levels of the HOMO -1, HOMO,
LUMO and LUMO+1 orbitals computed at the B3LYP/6-311 G(d,p)
level for the title compound.
As can be seen from the figure, both the highest occupied
molecular orbitals (HOMOs) and the lowest-lying unoccupied
molecular orbitals (LUMOs) are delocalized over nearly the entire
molecule and they are mostly the
p-antibonding type orbitals.
The value of the energy separation between the HOMO and LUMO
is 4.857 eV. This large HOMO–LUMO gap automatically means high
excitation energies for many excited state, a good stability and a
high chemical hardness for the tittle compound.
We have calculated 1H chemical shift values (with respect to
TMS) of 8.76–2.44 ppm for HF and 8.52–2.42 ppm for B3LYP meth-
ods with 6-311G(d,p) level, however, the experimental results

_
138
E. Inkaya et al. / Journal of Molecular Structure 1027 (2012) 133–139
Fig. 3. (a) 1H NMR spectrum of the title compound. (b) 13C NMR spectrum of the title compound.
Table 5
by these two methods. In order to define preferential position of 1H-
pyrazole system with respect to two (4-methylphenyl) groups, a
preliminary search of low-energy structures was performed using
AM1 computation as a function of selected torsion angles T
(C4AC5AC8AN1) and T (C14AC13AC10AN2). The respective value
of selected torsion angles are À122.8° and 168° in the X-ray struc-
ture, whereas corresponding value in optimized geometries is
À126.19° and 168.18° for HF/6-311G(d,p) and À133.96° and
175.53°for B3LYP/6-311G(d,p).
Molecular energy profiles with respect to rotations about
selected torsion angles are presented in Fig. S3 (see Supplementary
materials). According to the results the low energy domains for T
(C4AC5AC8AN1) are located at À160° À20° and 20° having energy
of 3.205, 3.206 and 3.205 eV., respectively, while they are located at
À130°, À50° and 50° having energy of 3.206, 3.206 and 3.207 eV,
respectively, for T (C14AC13AC10AN2). The energy difference be-
tween the most favorable and most unfavorable conformers, which
arisesfrom the rotationalpotential barrier calculatedwith respect to
the selected torsion angle, was calculated as 0.17660 eV for T
(C4AC5AC8AN1) and as 0.0658 eV for T (C14AC13AC10AN2),
when both selected degrees of torsional freedom are considered.
Experimental and theoretical 13C and 1H isotropic chemical shifts (ppm) for the title
compound.
Atom
Experimental (CDCl3)
Calculated (CDCl3)
HF/6-311G(d,p)
B3LYP/6-311G(d,p)
C1
C2
C3
C4
C5
C6
C7
C8
153.41
109.61
147.26
126.14
128.41
129.04
138.72
129.04
128.41
21.42
170.61
22.30
129.52
128.88
128.62
139.15
128.62
128.88
21.42
6.81
160.63
110.83
160.12
134.29
137.42
132.52
148.06
133.27
140.14
21.61
174.69
26.03
133.99
134.95
133.74
148.37
135.07
134.00
21.53
6.80
159.04
115.12
157.71
135.80
135.23
133.79
147.20
133.61
137.71
23.79
177.23
27.67
135.55
131.43
134.92
147.49
135.43
130.85
23.92
6.89
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
H2
H5
H6
7.43
7.30
7.86
7.69
7.63
7.56
3.8. Non-linear optical effects
H8
H9
7.28
7.80
7.63
Non-linear optical (NLO) effects arise from the interactions of
electromagnetic fields in various media to produce new fields al-
tered in phase, frequency, amplitude or other propagation charac-
teristics from the incident fields [51]. NLO is at the forefront of
current research because of its importance in providing the key
functions of frequency shifting, optical modulation, optical switch-
ing, optical logic, and optical memory for the emerging technolo-
gies in areas such as telecommunications, signal processing, and
optical interconnections [52–54].
7.40
8.00
7.89
H10a
H12a
H14
H15
H17
H18
H19a
RMSD
2.40a
2.50a
2.46a
2.83a
2.64a
2.69a
7.80
7.20
7.23
8.16
7.73
7.90
7.93
7.58
7.67
7.82
8.76
8.52
2.40a
2.44a
2.42a
1.296
1.011
Note: The atom numbering according to Fig. 1 used in the assignment of chemical
shifts.
The calculations of the mean linear polarizability (atot) and the
a
Average.
mean first hyperpolarizability (btot) from the Gaussian output have
been explained in detail previously and DFT has been extensively
used as an effective method to investigate the organic NLO materi-
3.7. Conformational analysis
als [55]. The total molecular dipole moment (
ability ( tot) and first-order hyperpolarizability (btot) of the title
compound were calculated at the B3LYP/6-311G(d,p) level. The
ltot), linear polariz-
Based on HF/6-311 G(d,p) and B3LYP/6-311 G(d,p) optimized
geometry, the total energy of the title compound has been calculated
a

_
E. Inkaya et al. / Journal of Molecular Structure 1027 (2012) 133–139
139
calculated values of ltot,
atot and btot are 1.46 D, 36.1399 Å3 and
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4. Conclusions
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Appendix A. Supplementary material
The figures related to the molecular electronic potential map,
molecular orbital surfaces and molecular energy profile of the title
compound are given in the supplementary material. CCDC 838067
contains the supplementary crystallographic data for the com-
pound reported in this paper. These data can be obtained free of
charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre (CCDC), 12 Union Road,
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