Experimental and theoretical studies of the molecular structure of 4-(3-(1H-imidazol-1-yl)propyl)-5-p-tolyl-2H-1,2,4-triazol-3(4H)-one

Article abstract of DOI:10.1016/j.molstruc.2010.09.018

The triazol-imidazol compound, 4-(3-(1H-imidazol-1-yl)propyl)-5-p-tolyl-2H- 1,2,4-triazol-3(4H)-one (3), (C₁₅H₁₇N₅O), was prepared and characterized by ¹H NMR, ¹³C NMR, IR and single-crystal X-ray diffraction. By using the density functional theory (DFT) method with 6-31G(d) basis set, the molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound (3) in the ground state were calculated and compared with the experimental data. The calculated results are show that the optimized geometry can well reproduce the crystal structure. X-ray, FT-IR and NMR spectral results of the title compound (3) indicate that the compound exists as keto form. To determine most favorable conformation as theoretically, molecular energy profile of the title compound (3) were obtained as a function of the selected torsion angles T(N1C8C7C6), T1 and T(C8N1C10C11), T2, which is varied from -180° to +180° in every 10 by semi-empirical (PM3) calculations. In addition, DFT calculations of the title compound (3), molecular electrostatic potential and frontier molecular orbitals were performed at B3LYP/6-31G(d) level of theory.

Full text of DOI:10.1016/j.molstruc.2010.09.018

Journal of Molecular Structure 984 (2010) 137–145
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Experimental and theoretical studies of the molecular structure of
4-(3-(1H-imidazol-1-yl)propyl)-5-p-tolyl-2H-1,2,4-triazol-3(4H)-one
c
c
d
Reßsat Ustabaßs a, Nevin Süleymanog˘lu b, , Hasan Tanak , Yelda Bingöl Alpaslan , Yasemin Ünver ,
⇑
Kemal Sancak d
a Department of Middle Education, Educational Faculty, Ondokuz Mayıs University, 55200 Atakum, Samsun, Turkey
b Atatürk Vocational High School, Gazi University, 06760 Çubuk, Ankara, Turkey
c Department of Physics, Faculty of Arts & Science, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
d Department of Chemistry, Faculty of Arts and Sciences, Karadeniz Teknik University, 61080-Trabzon, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 June 2010
Received in revised form 5 August 2010
Accepted 15 September 2010
Available online 29 September 2010
The triazol–imidazol compound, 4-(3-(1H-imidazol-1-yl)propyl)-5-p-tolyl-2H-1,2,4-triazol-3(4H)-one
(3), (C15H17N5O), was prepared and characterized by 1H NMR, 13C NMR, IR and single-crystal X-ray dif-
fraction. By using the density functional theory (DFT) method with 6-31G(d) basis set, the molecular
geometry, vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13C NMR chemical
shift values of the title compound (3) in the ground state were calculated and compared with the exper-
imental data. The calculated results are show that the optimized geometry can well reproduce the crystal
structure. X-ray, FT-IR and NMR spectral results of the title compound (3) indicate that the compound
exists as keto form. To determine most favorable conformation as theoretically, molecular energy profile
of the title compound (3) were obtained as a function of the selected torsion angles T(N1AC8AC7AC6), T1
and T(C8AN1AC10AC11), T2, which is varied from ꢀ180° to +180° in every 10 by semi-empirical (PM3)
calculations. In addition, DFT calculations of the title compound (3), molecular electrostatic potential and
frontier molecular orbitals were performed at B3LYP/6-31G(d) level of theory.
Keywords:
1,2,4-Triazol
Imidazol
IR and NMR spectroscopy
Density functional theory
Molecular electrostatic potential
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
notice of synthetic chemists as environmentally friendly organic
solvents, and continue to hold their attention as reaction catalysts
1,2,4-Triazole derivatives have been reported as fungicidal [1],
insecticidal [2], antimicrobial compounds [3] and some showed
antitumor activity [4,5] or are anticonvulsants [6], antidepressants
[7] and plant growth regulator anticoagulants [8]. It was reported
that compounds having triazole moieties such as vorozole, anas-
trozole and letrozole appear to be very effective aromatase inhibi-
tors, which are very useful for preventing breast cancer [9–11]. The
considerable biological importance of imidazoles and triazoles has
stimulated much work on these heterocycles and there are a vari-
ety of methods available for the synthesis of 1,2,4-triazole [12].
1,2,4-Triazole and imidazole are the hetero-rings of choice and
are essential structural features of many of the potent azole fungi-
cides [13]. It is also known that the triazole ring has been used in-
stead of imidazole, which is found in the structure of some
antagonist, anti-ulcer and antifungal drugs [14]. Ionic liquids, of
which imidazolium salts are most widely used, have gained initial
or promoters. Additionally, They have the ability to dissolve an
enormous range of inorganic, organic, and polymeric materials at
very high concentrations, are noncorrosive, and have low viscosi-
ties and no significant vapor pressures [15].
The main goal of our study is to synthesize the triazole com-
pound containing imidazol which are fundamental compounds in
the preparation of ionic liquids and used as a antimicrobial sub-
stance. There are both keto form and hydroxyl form of 1,2,4-triazol
in the theoretical but, keto form is more dominant form. In addi-
tion, IR and NMR spectral datas show that, while keto form is avail-
able, hydroxyl form is not existed [16]. In this study, we present
results of a detailed investigation of the synthesis and structural
characterization of 4-(3-(1H-imidazol-1-yl)propyl)-5-p-tolyl-2H-
1,2,4-triazol-3(4H)-one (3), (C15H17N5O), using single-crystal
X-ray diffraction, IR-NMR spectroscopy and quantum chemical
methods. The geometrical parameters, fundamental frequencies
and GIAO 1H and 13C NMR chemical shift values of the title com-
pound (3) in the ground state have been calculated by using the
DFT (B3LYP) method with 6-31G(d) basis set, and compared with
experimental data. The spectral datas of the title compound (3)
show that the compound exists as keto form.
⇑
Corresponding author.
E-mail address: nsuleymanoglu@gazi.edu.tr (N. Süleymanog˘lu).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.09.018

138
R. Ustabaßs et al. / Journal of Molecular Structure 984 (2010) 137–145
methods using SHELXS-97 [18]. Molecular plot was prepared with
ORTEPIII for Windows [19]. WinGX software [20] was used to pre-
pare material for publication. Details of the data collection condi-
tions and the parameters of refinement process are given in
Table 1.
2. Experimental and computational methods
2.1. Experimental
2.1.1. Physical measurements
In the determination of the melting point, a Gallenkamp melt-
ing point apparatus was used. By means of a Perkin-Elmer 1600
series FT-IR spectrophotometer using KBr pellets, the IR spectrum
of the title compound were recorded in the range 4000–
400 cmꢀ1 region. And finally, The 1H-, and 13C-Nuclear Magnetic
Resonance spectra were recorded on a Varian-Mercury 200 MHz
spectrometer, where TMS as an internal standard and DMSO-d6
as solvent are used. For elemental analysis, combustion/gas chro-
matography method was used. Elemental analyses were performed
on a Hewlett–Packard 185 CHN analyzer; their values agreed with
the calculated ones. A selected crystal with colourless and dimen-
sions of 0.60 ꢁ 0.59 ꢁ 0.46 mm was mounted on a STOE IPDS II
X-ray diffractometer. Data collection was performed at room tem-
2.1.2. Synthesis
Ethyl 2-(-ethoxy(p-tolyl)methylene] hydrazine carboxylate (1)
(2.50 g, 10 mmol) together with N-(3-aminopropyl) imidazole (2)
(1.25 g, 10 mmol) were heated without solvent in a sealed tube
for 2 h at 160–180°. Then, the mixture was cooled to r.t. and a solid
formed. The crude product was recrystallized using acetone/petro-
leum ether (1:2) (yield 70.20%) to afford the title compound (3).
M.P, 456–457 K. Anal. calc. for C15H17N5O: C, 63.59; H, 6.05; N,
24.72. Found: C, 63.65; H, 6.11; N, 24.79. EI-MS: 283.33 [M]+. Syn-
thetic pathway of the title compound (3) is shown in Scheme 1.
2.2. Computational methods
perature (293 K) using graphite monochromated Mo K
a radiation
(k = 0.71073 Å). The cell parameters were determined by using
X-AREA software [17]. The crystal structure was solved by direct
DFT and PM3 calculations were carried out using GAUSSIAN03
[21] program package. The geometry optimizations were per-
formed by using DFT ab initio method, starting from the experi-
mental structures. DFT calculations are performed without any
constraints on the molecule using the B3LYP hybrid exchange–cor-
relation function [22] with the aid of the 6-31G(d) basic set. The
conformational preferring of the title compound (3) is determined
by conformational analysis, selected degree of torsional freedoms,
T1 and T2 were varied from ꢀ180° to +180° in steps of 10°, and
molecular energy profiles were obtained at the semi-empirical
PM3 level [23,24]. B3LYP/6-31G(d) were used for the calculations
of the MEP [25–28] and frontier molecular orbitals (FMOs) were
carried out with the same level of theory B3LYP/6-31G(d). The cal-
culation of harmonic frequencies for the optimized geometry were
made at the same level and these were scaled by 0.9613 [29]. After
that, by using Gauss-View molecular visualization program [30],
the vibrational bands were assigned. Both the geometry of title
compound (3) and the geometry of tetramethylsilane (TMS) are
optimized. 1H and 13C NMR chemical shifts are calculated. For this
calculation, the standard GIAO/B3LYP/6-31G(d) (Gauge-Indepen-
dent Atomic Orbital) approach [31,32] with the program package
Gaussian 03W are used. In order to convert the 1H- and 13C-NMR
chemical shifts to TMS scale, the calculated absolute chemical
shielding of TMS are subtracted from these values. The calculated
absolute chemical shielding of TMS are 32.2 ppm and 189.84
ppm for B3LYP/6-31G(d), respectively.
Table 1
Crystal data and structure refinement parameters for the title compound (3).
Crystal data
Chemical formula
Mr
C15H17N5O
283.34
Cell setting, space group
Temperature (K)
a, b, c (Å)
Orthorhombic, Pbca
293
8.4234 (19), 32.3591 (3), 10.6577
(7)
2905.0 (7)
8
V (Å3)
Z
Dx(Mg cmꢀ3
)
1.296
Radiation type
Mo K
0.09
a
l
(mmꢀ1
)
Crystal form, colour
Prism, colourless
0.60 ꢁ 0.59 ꢁ 0.46
Crystal size (mm3)
Data collection
Diffractometer
STOE IPDS 2
Data collection method
No. of measured, independent and
observed reflections
Criterion for observed reflections
Rint
Scans method
43,108, 2750, 2312
I > 2r(I)
0.057
hmax
25.7o
Refinement
Refinement on
F2
R[F2 > 2
r
(F2)], wR(F2), S
0.039, 0.112, 1.08
2750 reflections
192
No. of reflection
3. Results and discussion
No. of parameters
H-atom treatment
Weighting scheme
Constrained to parent site
w = 1/
The synthesis of 4-(3-(1H-imidazol-1-yl)propyl)-5-p-tolyl-2H-
1,2,4-triazol-3(4H)-one (3) was obtained by the reaction of com-
pounds 1 and compound 2 (Scheme 1).The reaction pathway is
show that reaction started amino group of compound 2 attacked
carbonyl group of compound 1 with nucleophilic substitution
[r
2(F20)+(0.0652P)2 + 0.2022P]
P=(F20 þ 2F2c )/3
(D/r)
max
0.001
D
qmax
,
D
qmin (e Åꢀ3
)
0.13, ꢀ0.14
Scheme 1. Synthetic pathway for the preparation of the title compound (3).

R. Ustabaßs et al. / Journal of Molecular Structure 984 (2010) 137–145
139
reaction. Then, same amino group attack to imino carbon atom to
obtain triazol ring. Spectroscopic data of the product 3 confirmed
the success of the cyclization reaction. The EI–MS of compound 3
confirmed the proposed structure with a molecular ion peak at
m/z = 283.33. 1,2,4-Triazoles with exocyclic double bond can be
considered to exist in a tautomeric equilibrium between keto
(O@CANH) and hydroxy (HOAC@N) forms [33]. The IR datas indi-
cated the formation of compound 3 by the disappearance of CAO
stretching vibrations at 1235 cmꢀ1, and C@O belonging to the tria-
zole at 1710 cmꢀ1. The signal observed at 3383 cmꢀ1 in the IR spec-
tra of compound 3 was attributed to the NAH of triazol. In the 1H
NMR spectra, the existence of 3 was revealed by the disappearance
of form of the ester CH2O groups (4.36–4.40 ppm) in the precursor
(1) after the cyclization and the appearance of a new peak at
11.80 ppm integrating for one H-atom (exchangeable with D2O)
belonging to HAN [15]. More detailed information about the struc-
ture of compound 3 was provided by the 13C NMR spectra. The sig-
nals for the triazole C(8) and the C@O group C(9) are found at
146.49 and 155.63 ppm, respectively. FT-IR, 1H and 13C NMR spec-
tral datas of the title compound (3) show us that the compound ex-
ists as keto form.
3.1. Description of the crystal structure
The title compound (3) crystallizes in the orthorhombic, Pbca
space group with Z ¼ 8 in the unit cell. Fig. 1 shows ORTEPIII dia-
gram of the title compound (3) with the atom numbering scheme.
As revealed by X-ray structure analysis, each of tree rings in the ti-
tle compound (3) remains planar itself. The dihedral angles be-
tween triazol and benzene, triazol and imidazol rings are 53.58
(6)° and 15.62 (6)°, respectively. Methyl atom C1 deviates from
the benzene ring plane by 0.0309 (2) Å. The deviations from triazol
ring plane of atom O1 is ꢀ0.0361 (11) Å. The observed bond dis-
tances from X-ray analysis agree well with similar bonds reported
in the literature [34–36].
C3
C1
C2
C5
N3
C7
C4
N2
C6
C8
C9
N1
The crystal structure is stabilized by intermolecular interactions
and p–p stacking interaction. In crystal structure of the title com-
C14
N4
O1
C10
pound (3), there are three intermolecular hydrogen bonds (Table
2). The donor and acceptor distances are 2.816(2) (2) Å for
N2AH2AN5 [symmetry code: x, y, z + 1], 3.437 (2) Å for
C12AH12AO1 [symmetry code: ꢀx + 1/2, ꢀy + 1, zꢀ1/2] and
3.401(2) Å for C13AH13AO1 [symmetry code: ꢀx, ꢀy + 1, ꢀz; ];
respectively. Figs. 2a, 2b and 2c show forming of the sheet struc-
tures along the different directions. On the other hand, there is
C15
C12
C11
N5
C13
two intermolecular
p–p stacking interaction occurring between
Fig. 1. An ORTEP drawing of the title compound (3), with the atom numbering
scheme. Displacement ellipsoids are drawn at the 30% probability level.
the triazole rings and imidazole rings [(Cg1ꢂ ꢂ ꢂCg1 = 4.213 (13) Å;
symmetry code: ꢀ1/2 + x, y, 1/2 ꢀz); (Cg2ꢂ ꢂ ꢂCg2 = 4.265 (14) Å;
symmetry code: ꢀ1/2 + x, y, 3/2 ꢀz)]. Intermolecular hydrogen-
bonding and
p–p stacking interactions in the crystal structure
Table 2
are the most important feature in terms of supramolecular envi-
ronment of the title compound (3).
Hydrogen-bond geometry (Å, °).
DAHꢂ ꢂ ꢂA
DAH
Hꢂ ꢂ ꢂA
Dꢂ ꢂ ꢂA
DAHꢂ ꢂ ꢂA
C13AH13ꢂ ꢂ ꢂO1i
C12AH12Bꢂ ꢂ ꢂO1ii
N2AH2ꢂ ꢂ ꢂN5iii
0.93
0.97
0.86
2.53
2.54
1.99
3.401 (2)
3.437 (2)
2.816 (2)
157
154
162
3.2. Optimized geometry and conformational analysis
The first step for computational studies of the title compound
(3) was to determine the optimized geometry. The molecular
geometry without any restrictions from the results of X-ray diffrac-
Note: D: donor, A: acceptor. Symmetry transformations used to generate equivalent
atoms. (i) ꢀx, ꢀy + 1, ꢀz; (ii) ꢀx + 1/2, ꢀy + 1, zꢀ1/2; (iii) x, y, z + 1.
Fig. 2a. The compound (3) linked by C13-H13ꢂꢂꢂO1i (i: ꢀx, ꢀy + 1, ꢀz) hydrogen bond along the ab plane.

140
R. Ustabaßs et al. / Journal of Molecular Structure 984 (2010) 137–145
tion experimental were obtained. The second step, B3LYP (Becke’s
three parameter hybrid functional using the LYP correlation func-
tional) calculations at basis set 6-31G(d) [37].
The selected bond lengths, bond angles and torsion angles are
listed in Table 3 and compared with the experimental data of the
title compound (3). When the X-ray structure of the title
compound (3) is contrasted with its DFT optimized counterpart
(Fig. 3), it can be easily seen that they are slightly different each
other. Because, experimental results are based on the molecules
in the solid state while theoretical calculations are based on the
isolated molecules in the gas-phase. The RMSE fit of the atomic
position of the title compound (3) to those of its DFT optimized
counterpart is 0.0543 Å. As compared to experimental and
calculated results, the biggest deviation of the bond lengths is
ii
O1
C12
a
b
0
c
Fig. 2b. The compound (3) linked by C12-H12BꢂꢂꢂO1ii (ii: ꢀx + 1/2, ꢀy + 1, z ꢀ 1/2) hydrogen bond along the c axes.
c
N5iii
N2
0
b
a
Fig. 2c. The compound (3) linked by N2-H2ꢂꢂꢂN5iii (iii: x, y, z + 1) hydrogen bond along the c axes.

R. Ustabaßs et al. / Journal of Molecular Structure 984 (2010) 137–145
141
Table 3
profiles versus the selected torsion angles T1 and T2 are shown
in Fig. 4. The respective values of the selected degrees of torsional
freedom, T1 and T2 are 51.55(19)° and 99.86(16)° in X-ray struc-
ture, whereas the corresponding values in DFT optimized geometry
are 45.62° and 116.96°, respectively. These calculated values are in
good agreement with the experimental values.
As can be seen in Fig. 4, the low energy domains for T1 are lo-
cated at ꢀ130° and 50° having energy of 45.20 and 45.00 kcal/
mol, while they are located at ꢀ90° and 80° having energy of
45.48 and 44.96 kcal/mol, respectively, for T2. Energy difference
between the most favorable and unfavorable conformers, which
arises from rotational potential barrier calculated with respect to
the two selected torsion angles, is calculated as 89.79 kcal/mol
for T1 and as 51.47 kcal/mol for T2, when both selected degrees
of torsional freedom are considered.
Selected molecular structure parameters.
Parameters
Experimental
B3LYP 6-31G(d)
Bond lengths (Å)
N1AC8
N1AC9
N1AC10
N2AC9
N2AN3
O1AC9
N4AC13
N3AC8
1.3744 (16)
1.3896 (16)
1.4571 (16)
1.3453 (18)
1.3850 (16)
1.2274 (17)
1.3410(18)
1.3052 (17)
1.366 (2)
1.3927
1.4035
1.4676
1.3735
1.3739
1.2271
1.3700
1.3085
1.3767
1.3757
1.536
N5AC15
C15AC14
C12AC11
1.344 (2)
1.510 (2)
Bond angles (°)
C8AN1AC9
C8AN1AC10
C9AN1AC10
N3AC8AN1
N4AC12AC11
Torsion angles (°)
C10AN1AC8AC7
C8AN1AC10AC11
N1AC8AC7AC6
C10AN1AC8AN3
N3AN2AC9AO1
107.64 (11)
130.88 (11)
121.36 (11)
111.64 (12)
111.50 (12)
107.79
130.68
121.46
111.33
113.97
As compared to the rotation around the torsion angle along the
C8AC7 bond (T1) and the torsion angle along the N1AC10 bond
(T2), it can be said that this high potential barrier observed for
T1 is due to steric hindrances between benzene ring and the imida-
zol ring. Even so, it can be stated that the contribution to molecular
energy of torsion angle T1 is more than T2.
9.5 (2)
6.14
116.96
45.62
99.86 (16)
51.55 (19)
ꢀ175.06(13)
ꢀ178.31 (15)
ꢀ175.18
ꢀ177.70
3.3. Vibrational spectra
Harmonic vibrational frequencies calculated by using DFT/
B3LYP with 6-31G(d) basic set are given in Table 4, together with
Fig. 3. Atom-by-atom superimposition of the structures calculated (red) over the X-
ray structure (black) for the title compound (3). (For interpretation of the references
to colour in this figure legend, the reader is referred to the web version of this
article.)
0.032 Å at C15AC14 and the biggest deviation of the bond angles is
2.47° at N4AC12AC11. In the optimized geometry, the dihedral an-
gles between triazol and benzene, triazol and imidazol rings are
44.35°
and
19.55°,
respectively.
The
torsion
angles
C10AN1AC8AC7, C8AN1AC10AC11 and N1AC8AC7AC6 obtained
from DFT are 6.14°, 116.96° and 45.62°, respectively.
In order to define the preferential position of imidazol and ben-
zene rings, conformational analysis was carried out using PM3
computations as a function of the selected degrees of torsional
freedom T(N1AC8AC7AC6), T1 and T(C8AN1AC10AC11), T2 var-
ied from ꢀ180° to and 180° in step of 10°. The calculated energy
Fig. 4. Molecular energy profiles of the optimized counterpart of the title
compound (3) against the selected degrees of torsional freedom T(N1AC8AC7AC6),
T1, and T(C8AN1AC10AC11), T2, respectively.

142
R. Ustabaßs et al. / Journal of Molecular Structure 984 (2010) 137–145
Table 4
Comparison of the experimental and calculated vibrational frequencies (cmꢀ1).
Assignmentsa
Experiment
B3LYP/6-31G(d)
m
m
m
m
m
m
(NAH)
3383
3155–3116
3001
2971
1710
1515
1453
1351
1233
1105
977
3539
3166–3133
3009
2955
1759
1501
1452
1348
1217
1105
981
ring(CAH)
as(CAH3)
s(CAH2)
(C = O)
(C = C) +
(CAH2) +
(CH2ACH2) +
m
c
(C = N) +
ring(CAH)
(CAN) +
cring(CAH)
a
x
m
c
(NAH)
m(CAN) + d(CAH2)
cring(CAH) + d(CAH2) +
m(CAN)
x
x
x
x
(CAH3) + cring(CAH)
ring(CAH) +
ring(CAH)
ring(CAH) +
x
(CAH3)
823
776
737
811
772
710
x
(CAH3)
a
m, stretching; b, bending;
a
, scissoring;
c
, rocking;
x, wagging; d, twisting; s,
symmetric; as, asymmetric.
Fig. 6. Correlation graphic of calculated and experimental frequencies of the title
compound (3).
their experimental results. The FT-IR spectrum of the title com-
pound (3) is shown in Fig. 5. As can be seen in Table 4, The NAH
graphics given in Fig. 6. The correlation graphics in Fig. 6 shows
that experimental fundamentals are found to have a good correla-
tion with calculations. Our estimations on NAH stretching mode
contain ꢃ4.0% error on an average for B3LYP level. The other modes
in our results are estimated in a smaller error range.
stretching mode, calculated as 3539 cmꢀ1
, was observed at
3383 cmꢀ1 in the FT-IR spectrum. This difference between experi-
mental and calculated NAH stretching vibrations (156 cmꢀ1) can
be due to N2AH2ꢂ ꢂ ꢂN5 strong intermolecular hydrogen bond, that
calculations do not take into consideration. In the literature, the
some NAH stretching modes observed for the different substitu-
ent-triazole ring are 3470 cmꢀ1 [38] and 3417 cmꢀ1 [39] as exper-
imentally, and 3501 cmꢀ1 for B3LYP/6-311G(d,p) level [39] and
3566 cmꢀ1 [40] for B3LYP/6-31G(d). The CAH aromatic stretching
modes were calculated as 3166–3133 cmꢀ1, that were observed
at 3155–3116 cmꢀ1 (Table 4). The stretching C@O vibration gives
rise a band at 1710 cmꢀ1 in the infrared experimental spectrum,
while the calculated value is predicted 49 cmꢀ1 higher, at
1759 cmꢀ1. This difference given for C@O stretching vibration
can be explained by the existence of the CAHꢂ ꢂ ꢂO intermolecular
hydrogen bonds given in Table 2, because isolated molecules are
taken into consideration in calculations. The two bands attributed
3.4. NMR spectra
GIAO 1H and 13C chemical shift values (with respect to TMS) cal-
culated by the B3LYP method with 6-31G(d) basis set were com-
pared to the experimental 1H and 13C chemical shift values. The
results are given in Table 5.
Table 5
Theoretical and experimental 1H and 13C isotropic chemical shifts (with respect to
TMS, all values in ppm) for the title compound (3).
Atom
Experimental (ppm)
(DMSO-d6)
Calculated (ppm)
B3LYP/6-31G(d)
to the C@N stretching vibrations, obtained at 1575 and 1515 cmꢀ1
,
were calculated as 1566 and 1501 cmꢀ1, respectively (Table 4). The
above conclusions are in good agreement with the similar triazole
compounds [40,41].
C1
C2
C3
C4
C5
C6
C7
C8
21.11
124.73
127.81
127.81
129.71
129.71
140.31
146.49
155.63
60.53
30.20
43.65
140.11
119.62
129.92
2.36
22.14
134.34
124.24
123.07
123.54
121.74
119.92
141.74
143.25
40.34
30.59
42.45
127.05
113.14
121.67
1.95
Experimental frequencies of the title compound (3) were
compared with calculated vibrational frequencies by correlation
C9
C10
C11
C12
C13
C14
C15
H1A
H1B
H1C
H2
2.36
2.36
11.80
7.29
2.56
2.62
6.80
7.26
H3
H4
7.29
7.25
H5
7.44
7.63
H6
7.44
7.04
H10A
H10B
H11A
H11B
H12A
H12B
H13
H14
H15
3.93
3.93
2.15–2.20
2.15–2.20
3.63
3.63
7.57
7.12
6.87
3.66
3.65
1.43
3.01
3.23
3.70
6.9
5.03
6.29
Fig. 5. FT-IR spectrum of the title compound (3).

R. Ustabaßs et al. / Journal of Molecular Structure 984 (2010) 137–145
143
1H chemical shift values (with respect to TMS) have calculated
to be 7.63–1.43 ppm at B3LYP/6-31G(d) level, whereas the experi-
mental results are observed to be 11.80–2.15 ppm shown in Fig. 7.
The C(1)H3 protons of the title compound gave a singlet at
2.36 ppm. This statement was calculated at 1.95–2.62 ppm at
B3LYP level. The CAH signals of imidazole ring were observed at
7.57, 7.12 and 6.87 ppm. The NAH hydrogen in the 1,2,4-triazole
ring appears at 11.80 ppm, while this signal is observed computa-
tionally at 6.80 ppm (Table 5). This considerable difference be-
tween experimental and calculated chemical shifts is due to
N2AH2ꢂ ꢂ ꢂN5 strong intermolecular hydrogen bond, such as in
the IR spectrum, since the theoretical calculations are based on iso-
lated molecules in the gas-phase. In different substituent-1,2,4-tri-
azole, the H chemical shift of NAH were observed to be 11.33–
13.56 ppm [42]. In the 13C NMR spectra of the title compound,
the signals observed at 146,49 ppm and 155,63 ppm due to C8
and C9 atoms of the triazole ring were calculated as 141.74 and
143.25 ppm, respectively. Table 5 shows the other calculated
chemical shift values. As can be seen from Table 5, calculated 1H
and 13C chemical shift values of the title compound are generally
agreement with the experimental 1H and 13C shift data.
3.5. Molecular electrostatic potential
MEP at the B3LYP/6-31G(d) optimized geometry was calculated.
MEP is shown in Fig. 8. Following the approach previously reported
[43]. Here, the values of the MEP, which belong to the surface built
by the points with an electronic density q(r) = 0.001 a.u, were used.
Fig. 8. Molecular electrostatic potential map calculated at B3LYP/6-31G(d) level.
The negative (red and yellow) and the positive (blue) regions in the
MEP were related to electrophilic reactivity and nucleophilic reac-
tivity, respectively. As can be seen in Fig. 8, the negative regions of
the title compound (3) were observed around the carbonyl O1
atom, N5 atom of imidazole ring and N3 atom. If compared, the
negative V(r) values are ꢀ0.073 a.u. for N5 atom, ꢀ0.059 a.u. for
O1 atom and ꢀ0.044 a.u. for N3 atom. V(r) value for N5 atom is
found in the most negative region, where the others are in less
Fig. 7. The 1H NMR spectra of the title compound (3).

144
R. Ustabaßs et al. / Journal of Molecular Structure 984 (2010) 137–145
negative region. A maximum positive region localized on the
N2AH2 bond has value of +0.072 a.u. indicating a possible site
for nucleophilic attack. Considering these calculated results, the
MEP map shows that the negative potential sites are on electroneg-
ative, and positive potential sites around hydrogen atoms, respec-
tively. These sites give the information about the region from
where the compound can have intermolecular interactions. So,
Fig. 8 confirms the existence of intermolecular NAHꢂ ꢂ ꢂN and
CAHꢂ ꢂ ꢂO interactions.
compound (3). The considerable differences between experimental
and calculated results of IR and NMR can be attributed to the exis-
tence of NAHꢂ ꢂ ꢂN and CAHꢂ ꢂ ꢂO type intermolecular hydrogen
bonds in the crystal structure. The MEP map shows that the nega-
tive potential sites are on oxygen atoms as well as the positive po-
tential sites are around the hydrogen atoms and so MEP map
confirms the existence of intermolecular NAHꢂ ꢂ ꢂN and CAHꢂꢂꢂO
interactions. HOMO–LUMO gap with 4.97 eV indicates that the ti-
tle compound (3) has a good stability and a high chemical
hardness.
3.6. Frontier molecular orbitals
5. Supplementary data
The distributions and energy levels of the frontier molecular
orbitals (FMOs) were computed at the B3LYP/6-31G(d) level for
the title compound (3) and are shown in Fig. 9. As can be seen from
Fig. 9, while LUMO + 1 is principally delocalized among the atoms
of imidazol group, LUMO is delocalized among the atoms of both
triazol and imidazol groups. HOMO ꢀ 1 orbitals mainly localized
on the triazol and imidazol fragments, and HOMO is mainly local-
ized on the benzene fragment. Both the highest occupied molecu-
lar orbitals (HOMOs) and the lowest-lying unoccupied molecular
orbitals (LUMOs) are mainly localized on the rings indicating that
CCDC-757066 contains the supplementary crystallographic
data for the compound reported in this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retriev-
ing.html [or from the Cambridge Crystallographic Data Centre
(CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)
1223–336033; e-mail: deposit@ccdc.cam.ac.uk].
Acknowledgements
the HOMO–LUMO are mostly the
p-antibonding type orbitals
This study was supported by grants from Karadeniz Technical
University (Project No: 2007.111.002.11) and the scientific and
technological research council (TUBITAK Project No: 107T065) of
Turkey.
[44]. The magnitude of the energy separation between the HOMO
and LUMO is 4.97 eV. This large HOMO–LUMO gap is an indication
of a good stability and a high chemical hardness for the title com-
pound (3), means high excitation energies for many of excited
states.
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