Vibrational spectrum and assignments of 2-(4-methoxyphenyl)-1H-benzo[d]imidazole by ab initio Hartree-Fock and density functional methods

Article abstract of DOI:10.1016/j.saa.2007.07.027

The room temperature attenuated total reflection Fourier transform infrared spectrum of the 2-(4-methoxyphenyl)-1H-benzo[d]imidazole has been recorded with diamond/ZnSe prism. The conformational behaviour, structural stability of optimized geometry, frequ

Full text of DOI:10.1016/j.saa.2007.07.027

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 109–116
Vibrational spectrum and assignments of 2-(4-methoxyphenyl)-1
H-benzo[d]imidazole by ab initio Hartree–Fock and
density functional methods
b
Hakan Arslana,∗, Oztekin Algul
¨
¨
a Department of Chemistry, Faculty of Arts and Science, Mersin University, 33343-Mersin, Turkey
b Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Mersin University, 33169-Mersin, Turkey
Received 1 May 2007; received in revised form 28 June 2007; accepted 12 July 2007
Abstract
The room temperature attenuated total reflection Fourier transform infrared spectrum of the 2-(4-methoxyphenyl)-1H-benzo[d]imidazole has
been recorded with diamond/ZnSe prism. The conformational behaviour, structural stability of optimized geometry, frequency and intensity of
the vibrational bands of the title compound were investigated by utilizing ab initio calculations with 6-311G** basis set at HF, B3LYP, BLYP,
B3PW91 and mPW1PW91 levels. The harmonic vibrational frequencies were calculated and scaled values have been compared with experimental
IR spectrum. The observed and the calculated frequencies are found to be in good agreement. The theoretical vibrational spectra of the title
compound were interpreted by means of potential energy distributions using VEDA 4 program. Furthermore, the optimal uniform scaling factors
calculated for the title compound are 0.9120, 0.9596, 0.9660, 0.9699, and 0.9993 for HF, mPW1PW91, B3PW91, B3LYP and BLYP methods,
respectively.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Ab initio; HF; DFT; FT-IR ATR spectrum; Benzimidazole
1. Introduction
oped. The most popular synthesis approaches generally involve
the condensation of an arylenediamine with a carboxylic acid
or its derivative under harsh dehydrating reaction conditions
[11–14]. Another method is the condensation of an aldehyde
with arylendiamine [15–21]. These reactions are often carried
out under high pressure and require for long reaction time.
Therefore, discovery of mild and practical routes for the syn-
thesis of benzimidazoles continues to attract the attention of
researches. Some methods using transition metal catalyzed cou-
pling reactions to construct the benzimidazole nucleus have also
been reported [22]. A method starting from arlenediamine and
orthoester in the presence of Yb(OTf)3 [23], zeolite [24], or sul-
famic acid [25,26] at high temperature was also used for the
synthesis of benzimidazole derivatives.
On the other hand, microwave irridation is extensively used
for the rapid synthesis of a variety of heterocyclic compounds.
Some new methods reported for synthesizing 2-substituted ben-
zimidazoles under microwave irridation require polyphosphoric
acid as catalyst [27,28] and SiO2 as solid support [29]. Recently,
Villemin et al. [30] and Loupy et al. [31] reported a fast and
convenient synthesis of benzimidazoles by condensation of
orthoesters with o-phenylenediamine in dry medium and using
The benzimidazole compounds are of significant importance
to medicinal chemistry because of the broad spectrum of their
biological and pharmaceutical properties. The benzimidazole
group is present in various drugs such as omeprazole, mebenda-
zole, astemizole and emedastine difumarate [1]. Furthermore,
the benzimidazole derivatives can act as ligands to transition
metals for modeling biological systems [2–6].
Benzimidazoles bearing o- or p-substituted phenyl moi-
ety at position 2 have different biological activity such as
antihelmenthic, antifungal, antituberculous, anti-inflammatory
and antitumor activity [7–9]. For instance, a series of 2-
phenylbenzimidazole-4-carboxamides have shown in vitro and
in vivo antitumor activity and DNA-binding affinity [10].
The synthesis of benzimidazoles has received much attention
owing to the varied biological activity exhibited. Due to their
great importance, many synthesis strategies have been devel-
∗
Corresponding author. Tel.: +90 532 7073122.
E-mail address: arslanh@mersin.edu.tr (H. Arslan).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.07.027

¨
110
H. Arslan, O. Algu¨l / Spectrochimica Acta Part A 70 (2008) 109–116
Scheme 1. Synthesis reaction of the title compound.
montmorillonite KSF clay under mono-mode microwave irri-
dation. Penieres et al. [32] also obtained 2-alkylbenzimidazoles
using natural clay under infrared irridation in solvent-free con-
ditions.
our theoretical studies, in the present work we checked the rela-
tive performance of B3LYP, BLYP, B3PW91 and mPW1PW91
methods, as well as of HF for comparison, at the 6-311G**
level taking as a test compound 2-(4-methoxyphenyl)-1H-
benzo[d]imidazole (MPBI).
We have previously reported the synthesis of some biolog-
ically active 2-substituted benzimidazoles in connection with
our on-going project [2–5,33]. In continuation of our work on
bioactive benzimidazoles, in the present work, we have cal-
culated the vibrational frequencies and geometric parameters
of a benzimidazole derivative, 2-(4-methoxyphenyl)-1H-benzo
[d]imidazole, in the ground state to distinguish the fundamen-
tals from the experimentalvibrationalfrequenciesandgeometric
parameters, by using the Hartree–Fock (HF) [34], density func-
tional using Becke’s three-parameter hybrid functionals [35]
with the Lee, Yang, and Parr correlation functional methods
(B3LYP) [36], Becke’s exchange functional in combination with
the Lee, Yang and Parr correlation functional methods (BLYP)
[35,36], the Barone and Adamo’s Becke-style one-parameter
functional using the modified Perdew–Wang exchange and
Perdew–Wang 91 correlation method (mPW1PW91) [37,38],
Becke’s three-parameter exchange functional with Perdew and
Wang’s gradient-corrected correlation functional (B3PW91)
[35,39], with the standard 6-311G** basis set. Furthermore, we
interpreted the calculated spectra of in terms of potential energy
distributions (PEDs) and made the assignment of the experi-
mental bands due to PED analysis results. In continuation of
2. Experimental
2.1. Synthesis of
2-(4-methoxyphenyl)-1H-benzo[d]imidazole
In the present of the polyphosphoric acid, PPA, (5 mL),
the mixture of 4-methoxybenzoic acid (15 mmol) and 1,2-
phenylendiamine (10 mmol) was stirred and irridated in MW
(8 min) (100 W) (Scheme 1). After the reaction was completed,
the mixture was allowed to cool to room temperature and then
poured into 50 mL cold water. Stirring was continued for sev-
eral minutes and the mixture was neutralized with NaHCO3,
and then the solid products were filtered off. The crude prod-
ucts obtained were purified by recrystallization from EtOH/H2O
(1:1) and dried to give crystalline product in 74% yield mp
225 ◦C (mp 224–225 ◦C [14]). 1H NMR (CDCl3): δ 10.88 (br, s,
1H), 8.08 (d, J = 8.8 Hz, 2H), 7.74 (m, 2H), 7.48 (m, 2H), 7.24
(d, J = 8.8 Hz, 1H), 7.05–7.09 (m, 2H), 3.84 (s, 3H). 13C NMR
(400 MHz, DMSO-d6): δ 56.02, 115.06, 116.08, 122.45, 123.38,
128.70, 139.82, 152.04, 161.29. Anal. required for C14H12N2O
Fig. 1. The experimental and calculated (B3LYP/6-311G** level) FT-IR spectra of 2-(4-methoxyphenyl)-1H-benzo[d]imidazole.

¨
H. Arslan, O. Algu¨l / Spectrochimica Acta Part A 70 (2008) 109–116
111
Calc. C, 74.98; H. 5.39; N, 12.49; found C, 75.06; H, 5.48; N,
12.44%.
that the X-ray parameters [51] fairly well reproduce the geome-
try of the Conformer 1. Therefore, further in this paper, we focus
on this particular form of the title compound.
The optimized structure parameters of the title compound
calculated by ab initio and DFT methods listed in Table 2 are in
accordance with atom numbering scheme given in Fig. 2. The
crystal and molecular structure of the title compound have been
reported previously [51]. The geometric structure is monoclinic,
the space group P21/c, with the cell dimensions; a = 1◦1.354
2.2. Instrumentation
The room temperature attenuated total reflection Fourier
transform infrared (FT-IR ATR) solid state spectrum of the 2-
(4-methoxyphenyl)-1H-benzo[d]imidazole was recorded using
Varian FTS1000 FT-IR spectrometer with diamond/ZnSe prism
(4000–525 cm−1; number of scans: 250; resolution: 1 cm−1
(Fig. 1).
)
˚
˚
˚
(2) A, b = 10.562 (2) A, c = 9.868 (2) A, β = 112.22 (3) and
3
˚
V = 1095.5 (4) A . The structure parameters obtained by X-ray
single crystal diffraction method are given in Table 2. Also,
Table 2 compares the calculated geometric parameters with the
experimental data. Based on this comparison, the bond lengths
and angles calculated for the title compound showing good
agreement with experiment. However, according to our calcu-
lations, the optimized bond lengths obtained by DFT method
and bond angles by HF method show the best agreement with
the experimental values. The larges difference between experi-
mental and calculated DFT/B3LYP-6-311G** bond length and
2.3. Calculations details
The conformation analysis study was performed by Spartan
06 program package [40]. All the other calculations were per-
formed with the Gaussian 03W program package on a double
Xeon/3.2 GHz processor with 8 GB RAM [41]. The molecular
structure of the title compound, in the ground state, are opti-
mized by using HF, B3LYP, BLYP, mPW1PW91, and B3PW91
methods with the standard 6-311G** basis set. The vibra-
tional frequencies were also calculated with these methods.
The frequency values computed at these levels contain known
systematic errors [42]. These discrepancies can be corrected
either by the use of scaling equations [43,44] or directly scaling
the calculated wavenumbers with proper factor [45–48]. There-
fore, we have used the scaling factor values of 0.9051, 0.9679,
0.9934, 0.9631 and 0.9567 for HF, B3LYP, BLYP, B3PW91
and mPW1PW91, respectively [45–48]. We have also calcu-
lated optimal scaling factors for all investigated methods. The
assignment of the calculated wave numbers is aided by the ani-
mation option of GaussView 3.0 graphical interface for Gaussian
programs, which gives a visual presentation of the shape of
the vibrational modes [49]. Furthermore, theoretical vibrational
spectra of the title compound were interpreted by means of PEDs
using VEDA 4 program [50].
◦
˚
HF-6-311G** angle is 0.021 A and 1.88 , respectively.
3. Results and discussion
In this work, we performed full geometry optimization of the
title compound. To establish the most stable conformation as the
initial point for further calculations, the molecule was submit-
ted to a rigorous conformation analysis around the free rotation
bonds. This study was performed with the software Spartan 06
[40]. The structure of the title compound shows in Fig. 2 has
two conformations. Energetics, gathered in Table 1, show that
the Conformer 1 is the most stable. Also, comparison of the the-
oretical and experimental geometry of the title compound shows
Table 1
Energies of the different conformations of the title compound calculated at the
HF/6-311G** levela
Conformer
E (Hartree)
ꢀE (kcal/mol)
Dipole moment (D)
1
2
−720.82510
−720.81550
0.0000
6.0241
3.0038
4.8434
Fig. 2. Two stable conformers of the title compound calculated at HF/6-311G**
level and a view of the molecular structure of the MPBI, with displacement
ellipsoids drawn at the 50% probability level [51].
a
Total energies, E (with the zero-point vibrational energy correction).

¨
H. Arslan, O. Algu¨l / Spectrochimica Acta Part A 70 (2008) 109–116
112
Table 2
Optimized and experimental geometries of the title compound in the ground state
Parameters
Calculated
HF
Experimental [51]
DFT
B3LYP
BLYP
B3PW91
mPW1PW91
˚
Bond lengths (A)
R(1,2)
R(1,6)
R(2,3)
R(2,28)
R(3,4)
R(3,11)
R(4,5)
R(5,6)
R(11,12)
R(12,13)
R(12,28)
R(13,14)
R(13,15)
R(14,16)
R(15,18)
R(16,20)
R(18,20)
R(20,23)
R(23,24)
1.387
1.380
1.392
1.378
1.390
1.381
1.379
1.400
1.286
1.472
1.367
1.394
1.385
1.375
1.385
1.392
1.388
1.342
1.401
1.393
1.391
1.415
1.382
1.399
1.381
1.389
1.407
1.315
1.463
1.384
1.405
1.399
1.384
1.390
1.401
1.400
1.360
1.422
1.402
1.391
1.389
1.413
1.377
1.397
1.376
1.386
1.405
1.314
1.460
1.379
1.402
1.397
1.382
1.388
1.399
1.398
1.354
1.415
1.390
1.387
1.410
1.375
1.395
1.375
1.384
1.403
1.311
1.459
1.375
1.400
1.395
1.380
1.386
1.397
1.395
1.351
1.412
1.394(2)
1.387(2)
1.412(2)
1.380(2)
1.399(2)
1.397(2)
1.382(2)
1.404(2)
1.328(2)
1.468(2)
1.363(2)
1.394(2)
1.398(2)
1.388(2)
1.378(2)
1.390(2)
1.398(2)
1.363(2)
1.430(2)
1.402
1.429
1.392
1.409
1.391
1.399
1.416
1.331
1.468
1.399
1.416
1.412
1.394
1.399
1.411
1.410
1.376
1.442
Bond angles (◦)
A(2,1,6)
A(1,2,3)
A(1,2,28)
A(3,2,28)
A(2,3,4)
A(2,3,11)
A(4,3,11)
A(3,4,5)
116.80
122.57
132.85
104.58
119.96
109.97
130.07
118.04
121.26
121.36
105.72
124.71
112.82
122.47
122.43
119.36
118.21
121.08
121.34
120.16
119.77
119.43
115.90
124.67
119.04
106.90
116.78
122.55
133.00
104.44
119.64
110.28
130.08
118.14
121.41
121.47
105.79
124.77
112.02
123.21
122.90
119.05
118.06
121.10
121.39
120.24
119.83
119.39
115.81
124.81
118.59
107.47
116.77
122.57
133.01
104.41
119.55
110.44
130.01
118.17
121.45
121.49
105.77
124.89
111.79
123.33
122.99
119.11
117.91
121.17
121.46
120.24
119.84
119.39
115.56
125.06
118.29
107.59
116.71
122.63
132.98
104.39
119.61
110.35
130.04
118.10
121.45
121.50
105.61
124.62
112.15
123.23
123.00
118.90
118.10
121.08
121.37
120.23
119.83
119.38
115.88
124.74
118.26
107.50
116.70
122.63
132.97
104.39
119.63
110.34
130.03
118.09
121.45
121.50
105.58
124.58
112.23
123.19
122.97
118.86
118.17
121.04
121.34
120.22
119.81
119.42
115.91
124.67
118.19
107.46
116.91(15)
122.56(15)
132.14(15)
105.29(14)
119.41(15)
109.75(14)
130.84(15)
118.18(15)
121.75(15)
121.19(15)
104.46(13)
125.02(14)
113.36(14)
121.61(14)
120.55(15)
120.54(14)
118.88(15)
121.20(15)
120.40(15)
119.20(15)
120.16(15)
120.14(15)
115.41(15)
124.44(15)
117.43(13)
107.13(13)
A(4,5,6)
A(1,6,5)
A(3,11,12)
A(11,12,13)
A(11,12,28)
A(13,12,28)
A(12,13,14)
A(12,13,15)
A(14,13,15)
A(13,14,16)
A(13,15,18)
A(14,16,20)
A(15,18,20)
A(16,20,18)
A(16,20,23)
A(18,20,23)
A(20,23,24)
A(2,28,12)
The values of some thermodynamic parameters (such as
zero-point vibrational energy, total energy, thermal correction
to energy, etc.) of the title compound are listed in Table 3. It is
clear that, the zero-point vibrational energy is lower by the DFT
method than by the HF method. Additionally, total energy were
displayed the same trend.
We have calculated the theoretical vibrational spectra of 2-(4-
methoxyphenyl)-1H-benzo[d]imidazole by using HF, B3LYP,
BLYP, B3PW91 and mPW1PW91 methods with 6-311G**
basis set. Theoretical and experimental results of the title com-
pound are shown in Table 4 and supplementary materials in
TableS1–S4. Thevibrationalbandsassignmentshavebeenmade
by using both the animation option of GaussView 3.0 graphi-
cal interface for Gaussian programs [49] and VEDA 4 program
[50]. All the calculated spectra are in a good agreement with the
experimentalone. AllDFTmethodsaresuperiortoHFmethodin
terms of realistic reproduction of both band intensity distribution
and general spectral features.

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H. Arslan, O. Algu¨l / Spectrochimica Acta Part A 70 (2008) 109–116
113
Table 3
Some thermodynamic parameter for the title compound
Thermodynamic parameter
HF
DFT
B3LYP
BLYP
B3PW91
mPW1PW91
Total energy (a.u.)
Zero-point vibrational energy (kcal/mol)
Thermal correction to energy (kcal/mol)
−721.072115
155.00243
162.89582
−725.632093
144.73524
153.19891
−725.361665
140.07461
148.82204
−725.345957
143.30651
153.74736
−725.453406
146.32204
154.70745
Entropy (cal/mol K)
Total
Translational
Rotational
113.508
42.123
32.759
38.625
117.975
42.123
32.803
43.048
119.673
42.123
32.850
44.700
117.772
42.123
32.790
42.858
117.448
42.123
32.780
42.544
Vibrational
Dipole moment (D)
3.0038
2.9374
3.0069
2.9729
2.9595
culated band at 1136 cm−1 is attributed to CH3 rocking vibration
[59].
Although some vibrational analysis results for benzimida-
zole derivatives or its metal complexes can be found in the
literature [52–57], we cannot found any theoretical or experi-
mental vibrational data for 2-phenyl substituted benzimidazole
derivatives. Generally, the vibrational spectrum of benzimida-
zole derivatives is very complex. Benzimidazole derivatives
are not soluble in the common solvents which are used in
infrared spectrum recording studies. Therefore, the vibrational
spectra of the benzimidazole derivatives are recorded from
solid phase. It is clear that, the solid phase of the compounds
includes various crystal interactions. So, some of the vibra-
tional bands are observed different wavenumbers from the gas
phases. Benzimidazole derivatives are known to be strongly
associated through intermolecular hydrogen bonding. As an
example, title compound has an intermolecular N1–H1· · ·N2
The characteristic region of the benzimidazole derivatives
spectrum is 1500–1650 cm−1. The vibrational frequencies and
intensities for all substituted benzimidazole derivatives in this
range differ from the position of the substituent [58]. Gener-
ally, two bands around 1620 and 1590 cm−1 observed in this
range for benzimidazole derivatives. The observed vibrational
frequencies (1623 and 1585 cm−1) are generally intense because
of the conjugation between the benzene and imidazole rings. In
addition, the vibrational frequencies in this range vary with the
electronegativity of the substituent. The title compound shows
good agreement all these results since the 4-methoxy phenyl
group in position 2 is less apt to influence the vibrational fre-
quencies in this range. Also, we obtained another vibrational
frequency at 1612 and 1556 cm−1 which is come from 2-substi-
tution.
The benzimidazoles show strong vibrational bands in the
1500–1400 cm−1 region. These vibrational frequencies can be
attributed to skeletal in plane vibrations. The title compound
show two bands at 1476 and 1404 cm−1. These results confirmed
by Sundaraganesan et al. [54].
The identification of νC–N vibrations is a difficult task, since
the mixing of vibrations is possible in this region. However,
with the help of the animation option of GaussView 3.0 graphi-
cal interface for Gaussian programs and VEDA 4 program, the
νC–N vibrations are identified and assigned in this study. The IR
bands appearing at 1533 and 1501 cm−1 are assigned to νC N
vibrations and 1351 and 1268 cm−1 are assigned to νC–N vibra-
tions with the δCH for the title compound. All these results agree
with Sundaraganesan et al. [54].
˚
˚
hydrogen bond (H1· · ·N2 = 2.15 A, N1· · ·N2 = 3.005 (2) A
and N1· · ·H1—N2 = 173◦). These hydrogen bonds link the
molecules into chains running along the c axis. Free νNH stretch-
ing frequency usually is observed at about 3400 cm−1 [58].
The spectrum of the title compound show strong bands in
3200–2400 cm−1 which indicate polymeric association through
intermolecular hydrogen bonding. The νCH stretching vibrations
of the ring also occur in this range and cannot be distinguished
from the νNH stretching frequency.
The characteristic νCH stretching vibrations of heteroaro-
matic structure are expected to appear in 3000–3100 cm−1
frequency ranges. The νCH stretching vibrations of the title com-
pound were assigned to four bands observed at 3097, 3084,
3073, and 3060 cm−1 in the infrared spectrum. The B3LYP cal-
culated wavenumbers of these bands very well reproduced the
experimental ones. The difference between experimental and
calculated νCH is about 4, 6, 4, and 8 cm−1
.
The vibrational spectra of 2-substituted benzimidazoles show
a very intensive band around the 741 cm−1. This vibrational
mode is the most intensive in this region. It may be ascribed to
the out-of-plane γCH bending frequency. This result confirmed
by Sullivan [60].
A general better performance of B3LYP, BLYP, B3PW91
and mPW1PW91 versus HF can be quantitatively characterized
by using the mean absolute deviation, root mean square values
and coefficients of correlation (cc) between the calculated and
observed vibration frequencies and given in Tables 4 and S1–S4.
The root mean square (RMS) values were obtained in this study
For the assignments of CH3 group frequencies, eight fun-
damental vibrations can be associated to CH3 groups. Three
stretching, one umbrella, three deformations and one rocking
vibration mode designated the motion of the methyl group. The
CH3 asymmetric and symmetric stretching frequency is estab-
lished at 3047, 2954, and 2897 cm−1 in infrared spectra. These
assignments were supported by the literature [59]. The three
methyl hydrogen deformation modes are also well established
in the spectra. We have observed the methyl deformation mode
at 1469, 1449, and 1188 cm−1 in the infrared spectrum. The cal-

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H. Arslan, O. Algu¨l / Spectrochimica Acta Part A 70 (2008) 109–116
114
Table 4
Vibrational wavenumbers obtained for the title compound at B3LYP/6-311G** levela
Number Wave number
Experimental Unscaled
IR Inten.
Abs.
Red mass Force Constant Assignments, PED (%)d
Scaledb
Scaledc
Rel.
1
2
3
4
5
6
7
8
9
–
3105
3097
3097
3097
3084
3073
3060
3060
3047
2954
2897
1623
1612
1585
1556
1533
1501
1476
1469
1449
1436
1423
1404
1373
1351
1317
1300
1277
1268
1252
1225
1207
1188
1182
1151
1127
1116
1110
1067
1029
1009
996
3669
3211
3198
3196
3195
3185
3173
3164
3164
3136
3065
3006
1664
1655
1624
1613
1578
1531
1517
1505
1493
1480
1475
1455
1424
1389
1343
1334
1318
1302
1286
1251
1249
1205
1197
1171
1171
1140
1135
1097
1060
1029
1024
990
3559
3114
3101
3100
3099
3090
3077
3068
3068
3042
2973
2915
1614
1605
1575
1564
1530
1484
1471
1460
1448
1435
1431
1411
1381
1347
1302
1293
1278
1263
1248
1213
1212
1169
1161
1136
1136
1106
1101
1064
1028
998
3551
3108
3095
3093
3092
3083
3071
3062
3062
3036
2967
2909
1611
1602
1572
1561
1527
1481
1468
1457
1445
1432
1428
1408
1378
1345
1299
1291
1276
1260
1245
1211
1209
1167
1159
1133
1133
1103
1098
1062
1026
996
39
7
5
10
2
1
2
5
7
3
3
2
1.08
1.09
1.09
1.09
1.10
1.09
1.09
1.09
1.09
1.10
1.11
1.03
6.63
5.85
6.35
6.73
4.27
2.57
3.21
1.09
1.05
1.28
2.59
2.87
2.89
4.75
3.71
1.51
2.89
4.23
3.77
2.67
1.98
1.40
1.17
1.15
1.27
1.38
1.45
2.58
6.93
2.13
2.71
1.34
1.27
7.76
1.32
1.37
6.02
1.54
1.71
5.02
1.32
5.29
3.49
2.09
2.15
4.01
6.72
6.23
6.75
3.76
8.57
6.65
6.56
6.57
6.59
6.54
6.46
6.41
6.41
6.37
6.13
5.51
10.81
9.44
9.87
10.32
6.26
3.54
4.36
1.46
1.37
1.66
3.32
3.58
3.45
5.41
3.94
1.58
2.96
4.22
3.67
2.46
1.82
1.20
0.98
0.93
1.03
1.05
1.10
1.83
4.59
1.33
1.67
0.77
0.72
4.27
0.69
0.71
2.95
0.67
0.73
2.05
0.52
2.00
1.25
0.70
0.70
1.19
1.69
1.50
1.58
0.77
νNH (100)
νCH, sym, ring 1, (99)
νCH, asym, ring 1, (99)
νCH, asym, ring 1, (79)
νCH, sym, ring 3, (87)
νCH, asym, ring 3, (94)
νCH, asym, ring 3, (91)
νCH, asym, ring 1,3, (95)
νCH, asym, ring 1,3, (97)
νCH, asym, CH3, (92)
νCH, asym, CH3, (100)
νCH, sym, CH3, (96)
νC=C, ring 3, (47)
νC C, ring 1, (41)
νC C, ring 2,3, (12) + δCNC (13)
νC C, ring 1, (41)
νCN (13) + νCC (19)
νCN (12)
νCC (16) + δCH (25)
δCH3 , deform. (86)
δCH3 , deform. (93)
δCH3 , umbrella (71)
6
21
27
12
11
7
26
39
67
20
118
9
14
6
164
24
87
8
21
23
89
32
65
7
2
50
5
395
6
2
4
98
1
1
6
9
3
77
6
0
0
0
0
0
2
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
7
10
17
5
30
2
3
1
42
6
22
2
5
6
22
8
17
2
1
13
1
100
2
0
1
25
0
0
1
2
1
19
1
0
0
0
0
0
0
1
0
12
0
δCH (19) + δCNC (10) + νCC (11)
3
νCC (23) + δCH (21)
δCH (14) + δCNH (16)
νCN (22) + νCC (10) + δCNC (10) + δCH (11)
νCC (23) + δCH (10), ring 1
δCH (66), ring 1
νCC (14) + δCH (11), ring 1
νCN (33) + νCC (17) + δCH (10), ring 3
νCO (35)
νCC (10) + νCN (12) + δCH (33), ring 3
νCC (11) + δCNH (33)
δCH3 , deform. (78)
δCH (67), ring 1
δCH (53), ring 3
δCH3 , rock. (63)
νCC (10) + δCH (39), ring 1
νCC (25) + δCH (32), ring 3
νCN (30) + δCNH (15)
νO–CH (72)
3
δCNC (13) + δCCC (12) + δCCN (16)
δCCC (66)
γCH, (88), ring 1
γCH, (71), ring 3
νCN (16) + δCNC (27)
γCH, (94), ring 1
γCH, (78), ring 3
δCCC (30) + δCCN (36)
γCH, (81), ring 3
993
961
949
938
913
909
885
833
825
808
793
777
757
732
723
687
991
959
947
936
911
907
883
831
823
807
791
775
756
730
722
686
959
933
924
922
901
899
844
834
812
786
763
745
741
734
707
637
979
967
941
937
912
859
851
833
818
801
781
754
746
709
654
640
1
48
0
6
17
7
60
16
0
3
8
γCH, (54), ring 1 + γC, (17), C20
νCC (22) + δNCN (14)
γCH, (83), ring 3
1
4
2
15
4
0
1
2
1
νCC (10) + νCO (15)
τCC (18) + τCN (25) + γC (27)
γCH, (45), ring 3 + γC, (14), C12
γCH, (40), ring 3 + τCC (13)
τCC (55), ring 1 + γC, (17), C12
δCCC (43) + δCCO (11)
νCC (10) + δCCC (19), ring 1
νCC (36) + δCNC (34)
635
621
611
572
633
619
610
571
627
615
582
630
590
2
0
0
γCH (10) + τCC (39) + γC (21)

¨
H. Arslan, O. Algu¨l / Spectrochimica Acta Part A 70 (2008) 109–116
115
Table 4 (Continued )
Number
Wave number
IR Inten.
Abs.
Red mass
Force Constant
Assignments, PED (%)d
Experimental
Unscaled
Scaledb
Scaledc
Rel.
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
556
549
521
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
564
542
534
476
445
435
410
383
343
281
266
256
233
221
146
92
547
526
518
462
432
422
398
371
333
272
258
248
225
214
142
90
546
525
517
461
431
421
397
370
332
272
257
248
225
213
142
89
10
26
28
3
17
25
24
1
3
0
1
4
0
0
4
1
2
0
5
2
7
7
1
4
6
6
0
1
0
0
1
0
0
1
0
0
0
1
5.69
3.84
2.72
4.48
2.77
1.82
1.90
5.54
4.36
3.16
5.95
4.68
1.37
3.60
4.74
3.87
4.76
4.91
3.69
1.07
0.67
0.46
0.60
0.32
0.20
0.19
0.48
0.30
0.15
0.25
0.18
0.04
0.10
0.06
0.02
0.02
0.01
0.00
δCCC (23) + δCCN (13) + δCCO (23)
δCCN (18) + δCCC (13)
γC (37)
δCCO (15) + δCCC (29)
τCN (10) + γC (42)
τCN (44) + γC (17)
τCN (40) + τCC (27)
τCC (35) + τCN (14) + γC (10)
δCCC (27) + δCOC (17)
τCO (14) + τCC (18) + γC (12)
δCCC (26)
τCC (17) + τCN (39) + γC (29)
τCO (48)
δCCO (26) + δOCO (25)
τCC (31) + τCO (22)
τCO (55)
86
45
17
83
44
17
83
44
17
δCCN (34) + δCCC (35)
τCC (13) + γC (29)
τCC (84)
–
r
0.9999
41.86
0.9999
8.58
0.9999
47.79
Mean absolute
deviation
RMSmol
RMSover
Scaling factor
51.60
45.86
1.0000
10.15
9.02
0.9699
53.24
47.33
0.9679
a
Harmonic frequencies (in cm−1), IR intensities (km mol−1), reduced masses (amu) and force constants (m dyn A−1).
Scaling factor = 0.9699 (calculated in this study).
Scaling factor = 0.9679 [46].
˚
b
c
d
ν, stretching; δ, bending; ipb, in-plane bending; γ, out-of-plane bending; τ, torsion; sym, symmetric; asym, asymmetric; ring 1: C13–C14–C16–C20–C18–C15;
ring 2: C12–N11–C3–C2–N28; Ring 3: C2–C3–C4–C5–C6–C1; PED less than 10% are not shown.
using the Eqs. (12) and (13) from Ref. [45]. The cc values for all
three DFT methods were bigger than 0.9998, whereas for HF it
was 0.9996: these values are very close to those reported for the
literature data [61–70].
These results indicate that the DFT calculations approximate
the observed fundamental frequencies much better than the HF
results. Furthermore, the B3LYP method calculations approx-
imate the observed fundamental frequencies much better than
the other investigated DFT methods results. The small differ-
ence between experimental and calculated vibrational modes
is observed. We note that the experimental results belong
to solid phase and theoretical calculations belong to gaseous
phase.
Finally, one should mention scaling factors, which are crucial
for IR spectral predictions. To calculate optimal scaling fac-
tors, we employed a least-square procedure using the Eq. (10)
from Ref. [45]. Only single (uniform) scaling factors were calcu-
lated, without discrimination for different vibrations. The values
obtained are 0.9120, 0.9596, 0.9660, 0.9699, and 0.9993 for HF,
mPW1PW91, B3PW91, B3LYP and BLYP, respectively. They
are very close to those recommended by the literature [45–48]
for the same levels of theory. Thus, for future IR spectral pre-
dictions for unknown derivatives of the title compound, one
can recommend scaling factors of 0.912, 0.960, 0.966, 0.970,
and 0.999 for HF, mPW1PW91, B3PW91, B3LYP, and BLYP,
respectively.
4. Conclusions
The ground state geometries were optimized using the HF,
B3LYP, BLYP, B3PW91 and mPW1PW91 methods with the
6-311G** basis set. The vibrational frequencies were also cal-
culated with these methods. IR spectrum of the title compound
computed is in a good agreement with its observed FT-IR spec-
trum. The correlation between the calculated and experimental
vibration frequencies is characterized by the coefficients of big-
ger than 0.9998 for all three DFT methods and 0.9996 for HF.
Optimal uniform scaling factors calculated for the title com-
pound are 0.9120, 0.9596, 0.9660, 0.9699, and 0.9993 for HF,
mPW1PW91, B3PW91, B3LYP and, BLYP, respectively. For IR
spectrum predictions for the title compound type derivatives, any
of the three hybrid functions can be equally successfully used.
Taking into account small variations of the scaling factors for the
derivatives of the title compound, for future IR spectral predic-
tions for unknown compounds of this class, one can recommend
scaling factors of 0.912, 0.960, 0.966, 0.970, and 0.999 for HF,
mPW1PW91, B3PW91, B3LYP, and BLYP, respectively.
Acknowledgements
This work was supported by the Mersin University
Research Fund (project no: BAP.ECZ.F.TB. (HA) 2006-1 and
BAP.ECZ.F.MB. (OA) 2006-3).
¨

¨
116
H. Arslan, O. Algu¨l / Spectrochimica Acta Part A 70 (2008) 109–116
Appendix A. Supplementary data
Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain,
O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C.
Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala,
Q. Cui, K. Morokuma, P. Salvador, J.J. Dannenberg, D.K. Malick, A.D.
Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G.
Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.
Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng,
A. Nanayakkara, C. Gonzalez, M. Challacombe, P.M.W. Gill, B. John-
son, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M. Head-Gordon,
E.S. Replogle, J.A. Pople, Gaussian 03 Revision C. 02, Gaussian Inc.,
Pittsburgh, PA, 2003.
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.saa.2007.07.027.
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