Polarity and structure of 2-(1-methylbenzimidazol-2-yl)-1-phenyl- and -1,2-diphenyl-1-nitroethenes

Article abstract of DOI:10.1134/S1070363212050192

Polarity of 2-(1-methylbenzimidazol-2-yl)-1-phenyl- and -1,2-diphenyl-1-nitroethenes was determined and their structure was studied using electronic and ¹H, ¹³C NMR spectroscopy, dipole moments measuring, XRD analysis, and quantum-ch

Full text of DOI:10.1134/S1070363212050192

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 5, pp. 911–920. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © E.A. Ishmaeva, Ya.A. Vereshchagina, D.V. Chachkov, O.S. Vasil’eva, E.S. Ostroglyadov, A.A. Nikonorov, I.A. Litvinov,
D.B. Krivolapov, A.Z. Alimova, V.M. Berestovitskaya, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 5, pp. 833–843.
Polarity and Structure of 2-(1-Methylbenzimidazol-2-yl)-
1-phenyl- and -1,2-Diphenyl-1-nitroethenes
E. A. Ishmaevaa, Ya. A. Vereshchaginaa, D. V. Chachkovb, O. S. Vasil’evac,
E. S. Ostroglyadovc, A. A. Nikonorovc, I. A. Litvinovd,
D. B. Krivolapovd, A. Z. Alimovaa, and V. M. Berestovitskayac
a Kazan (Volga Region) Federal University, ul. Kremlevskaya 18, Kazan, Tatarstan, 420008 Russia
e-mail: elenishmaeva@gmail.com
b Joint Supercomputer Center of the Russian Academy of Sciences (Kazan Branch),
Kazan, Tatarstan, Russia
c Herzen Russian State Pedagogical University, St. Petersburg, Russia
d Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences, Kazan,
Tatarstan, Russia
Received July 11, 2011
Abstract—Polarity of 2-(1-methylbenzimidazol-2-yl)-1-phenyl- and -1,2-diphenyl-1-nitroethenes was
1
determined and their structure was studied using electronic and H, 13C NMR spectroscopy, dipole moments
measuring, XRD analysis, and quantum-chemical calculations. It was shown that the 2-(1-methylbenzimidazol-
2-yl)-1-nitro-1-phenylethene has Z-configuration both in crystal and solution. The nitro group and
benzimidazole substituent in its molecule are removed from the plane of the double bond. For 1,2-diphenyl-1-
nitroethene E-structure is typical.
DOI: 10.1134/S1070363212050192
It is known that nitrogen-containing heterocycles
like indole, pyridine, and benzimidazole are potential
holders of biological activity [1] and are widely
distributed in nature. They are part of the molecules of
many drugs: diazolin, cardiamine, indopan, dibazol,
and others [2–5]. The convenient starting reagents for
the synthesis of compounds containing the mentioned
pharmacophoric heterocycles are the corresponding 2-
hetero-1-nitroethenes. Therefore, the study of structure
and properties of 2-hetero-1-nitroethenes is an urgent
task of modern organic chemistry.
Nitroalkene with N-methylbenzimidazolyl substi-
tuent I was isolated as a mixture of E- and Z-isomers
in a ratio of 5:1 from the synthesis carried out by
method [8] that we somewhat modified. At the recrys-
talization of the E-isomer from acetone or alcohol it
completely transformed into Z-isomer (Figs. 1, 2).
N
N
N
N
C6H5
NO2
NO2
We have previously investigated the structure of 2-
(indol-3-yl)-, 2-(pyridin-3-yl)- and 2-(1-methylbenz-
imidazol-2-yl)-1-nitroethenes [6, 7]. These highly con-
jugated systems have the E-configuration, the mole-
cules are almost flat.
H3C
H3C
2
2
1
1
HA
E-I
HA
Z-I
C6H5
The Z-isomer is quite stable and does not change in
time, while, unfortunately, we failed to separate the E-
isomer from the mixture.
This paper considers the disubstituted nitroalkenes:
we first obtained and studied 2-(1-methylbenzimi-
dazol-2-yl)-1-nitro-1-phenylethene I [8], as well as the
previously known 1,2-diphenyl-1- nitroethene II [9]
using a complex of physical methods and quantum-
chemical calculations.
1,2-Diphenyl-1-nitroethene (nitrostylbene) II was
prepared according to the method [9] that we slightly
modified. It exists mainly as the E-isomer.
911

912
ISHMAEVA et al.
δ, ppm
δ, ppm
1
Fig. 1. 1H NMR spectrum of (Z)-2-(1-methylbenzimidazol-
2-yl)-1-nitro-1-phenylethene I.
Fig. 2. H NMR spectrum of a mixture E:Z = 5:1 of the 2-
(1-methylbenzimidazol-2-yl)-1-nitro-1-phenylethene I isomers.
1
in the H–13C HMQC spectrum of the Z-nitroethene I
C6H5
HA
NO2
C6H5
HA
C6H5
NO2
(Fig. 3) there is a correlation between the olefinic
proton HA (6.82 ppm) and C2 nucleus (106.14 ppm). A
similar correlation is also found in the spectrum of E-
forms: the cross-peaks between the proton HA
(8.17 ppm) and C2 nucleus (120.50 ppm).
C6H5
E
Z
Preference of the the Z-configuration in nitroalkene
I and E in the case of II is connected, apparently, with
lesser steric strain in these structures, and certain
contribution from the conjugation of aromatic rings
with the nitro group to the electronic organization of
the molecule II in this geometric form.
The validity of assignment of the chemical shifts of
carbon atoms С1 in the spectra of compounds I and II
is confirmed using the method of H–13C HMBC.
1
Thus, the H–13C HMBC spectrum of the Z-form of
1
nitroethene I (Fig. 4) shows a correlation between the
olefinic proton HA (6.82 ppm) and carbon nucleus C1
(130.37 ppm). A similar correlation is observed in the
1H–13C HMBC spectra between the proton HA
(8.17 ppm) and C1 nucleus (130.33 ppm) for the E-
forms.
The main test for assignment of the nitroalkene
molecules under considerations to E- or Z-series is the
chemical shift of olefinic protons signals in the H
1
NMR spectra: a downfield (8.17 ppm) shift of the
olefinic proton signal of the E-isomer (in which this
proton experiences a strong influence of the cis-located
nitro group), and a shift of related signal to rather
stronger field (6.82 ppm) in the spectrum of the Z-
isomer in which the olefinic proton is removed from
the nitro group and suffers obviously the anisotropic
effect of the benzene ring [10, 11] (Table 1, Figs. 1, 2).
To assess the polarity of the disubstituted nitro-
alkenes I and II we determined their dipole moments.
The coefficients in the calculating equations and the
orientational polarization are shown in Table 2.
Table 3 shows the values of dipole moments
calculated by the vector-additive scheme and theo-
retical dipole moments of the investigated nitro-
ethenes, as well as the relative energies of Ζ- and Ε-
isomers. For convenience, the experimental values are
repeated here. As is obvious from
In the 13C NMR spectrum (Table 1) of the Z-isomer
of compound I the signals of the carbon atoms in the
olefinic fragment appear at 130.37 (C1) and 106.14
ppm (C2), while in the spectrum of the E-form is
observed a downfield shift of the C2 signal (120.50
ppm). The correctness of interpretation of the 13C
NMR spectra is confirmed using the methods of two-
dimensional heteronuclear correlation spectroscopy
Tables 2 and 3, polarities of the studied nitroethenes
are quite high. Both compounds are brightly colored
and have a limited solubility, therefore the dielectric
permeabilities of both compounds were measured in
dioxane, for compound II also benzene. The dipole
1H–13C HMQC and H–13C HMBC (Figs. 3, 4). Thus,
1
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POLARITY AND STRUCTURE OF 2-(1-METHYLBENZIMIDAZOL-2-YL)-1-PHENYL-
913
Table 1. Spectral characteristics of 2-(1-methylbenzimidazol-2-yl)-1-nitro-1-phenylethene I and 1,2-diphenyl-1-nitroethene II
Ph
H
A
NO
R
2
Electronic
spectra, in
CH3CN
δH, ppm, CDCl3
δC, ppm, CDCl3
mp,
°С
Yield,
%
R
λmax
nm
,
R
HA
Me
R, Ph
С1
С2
Me
ε
N
Z-I
210–212
83
Bza: 7.30, 6.82 3.87 109.42, 120.92, 123.07, 130.37 106.14 30.19 260 13000
7.80
Ph: 7.50,
7.54;
124.01, 125.88, 129.34,
131.30, 143.65, 144.21,
153.85
337 37000
N
CH
3
E-I
155–157a
74–75
87
70
7.20–7.70
8.17 3.63 109.79, 121.06, 123.31, 130.33 120.50 30.63 352 23000
124.58, 128.58, 130.74,
135.86, 154.91
128.83, 129.35, 130.18, 149.71 134.97
130.66, 130.89, 131.24,
131.28
E-II
С6Н5
7.23, 7.50, 8.23
7.09, 7.33
–
–
226b 10700
318 11000
a
The melting point is given for a mixture of E:Z = 5:1. b The figures for compound II are close to those published in [21, 22].
moment of the benzimidazole-containing nitroethene I
could not be determined in benzene because of its low
solubility.
obtained by XRD analysis of 2-(1-methylbenzimi-
dazol-2-yl)-1-nitro-1-phenylethene I were used (Table 4),
as well as the following dipole moments of bonds and
groups: m(Ph–Csp2) = 0.33 D (calculated from μexp
(CH2=CHC6H5) [12]), m(H–Csp2) = 0.70 D [13] m
(Csp2–NO2) = 2.81 D (calculated from the μexp
For calculation of the dipole moments using the
vector-additive scheme the values of bond angles
δ, ppm
δ, ppm
Fig. 3. 1H–13C HMQC spectrum of (Z)-2-(1-methylbenzimidazol-2-yl)-1-nitro-1-phenylethene I.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

914
ISHMAEVA et al.
δ, ppm
δ, ppm
Fig. 4. 1H–13C HMBC spectrum of (Z)-2-(1-methylbenzimidazol-2-yl)-1-nitro-1-phenylethene I.
(CH2=CHNO2) [12]), m(Het–Csp2) = 3.34 D (cal-
culated from the μexp of N-methylbenzimidazole [12]).
known, gives a fairly wide deviations of calculated
geometric parameters from the experimental data. On
the other hand, it reproduces experimental dipole
moments somewhat better than DFT, as was shown in
[19]. In turn, the DFT method gives some less
consistent values of the dipole moments for these
compounds, but agrees with the XRD data by the bond
lengths and angles (Tables 4–6).
Quantum-chemical calculations were carried out by
HF [14] and hybrid DFT methods B3LYP and
B3PW91 [15–17] using the basis set 6-31G(d) and 6-
311++G(df,p) (Table 3) within Gaussian 03 software
[18]. The simplest nonempirical HF method, as is
Table 2. The coefficients of the calculation equations and the orientation polarization of nitroethenes
Comp. no.
Solvent
Dioxane
Benzene
Dioxane
α
γ
Рor, cm3
1022.357
656.895
746.873
μ, D
7.07
5.67
6.05
24.669
16.868
21.387
2.045
1.345
1.155
I
II
Table 3. Dipole moments (D) and relative energies (ΔE, kJ mol–1) of Ζ- and Ε-isomers of 2-(1-methylbenzimidazol-2-yl)-1-
nitro-1-phenylethene I and 1-nitro-1,2-dphenylethene
μtheor
ΔE
ΔE
B3PW91/
6-311++G(df,p)
Comp.
no.
μcalc
μexp
μexp
μ
theorB3PW91/
μtheor
ΔE
Isomer
B3PW91/ B3PW91/
6-31G(d) 6-31G(d)
(vector) (benzene) (dioxane)
6-311++G(df,p)
HF/6-31G(d) HF/6-31G(d)
E
Z
E
Z
5.94
3.63
2.93
3.51
–
7.07
6.05
5.01
6.48
5.35
3.32
0.0
11.4
0.0
5.40
6.73
5.60
3.52
0.0
9.5
4.99
6.90
5.75
3.99
0.0
8.4
I
5.67
0.0
0.0
II
14.4
13.1
13.5
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

POLARITY AND STRUCTURE OF 2-(1-METHYLBENZIMIDAZOL-2-YL)-1-PHENYL-
915
Table 4. Bond angles (ω, deg) in molecule I
Analysis of the data in Table 3 shows, firstly, that
all used quantum-chemical methods reflect quite well
reflect the polarity of the compounds and secondly,
from the data follows that in the studied samples in
each case one form (Z or E) predominantes.
Angle
C3N4C5
ω
Angle
C14C15C16
ω
103.7(4)
120.0(7)
C3N11C10
106.0(4)
127.6(4)
C15C16C17
119.3(6)
121.3(6)
C3N11C12
C16C17C18
C10N11C12
O20N19O21
O20N19C1
O21N19C1
N19C1C2
126.3(4)
125.1(6)
C13C18C17
C1C2H2
C3C2H2
C5C6H6
C7C6H6
C6C7H7
C8C7H7
C7C8H8
C9C8H8
C8C9H9
119.9(6)
117(4)
Attention merits the high polarity of compound I:
its μexp 7.7 D differs from the theoretical dipole
moments and even more from the values calculated by
the vector-additive scheme (5.94, 3.63 D). It is well
known [20] that the simultaneous presence of the
donor and acceptor groups in the vicinal positions of
an unsaturated compound (in our case, the
benzimidazole ring and the nitro group) can result in a
significant increase in the experimental dipole moment
117.4(5)
117.5(5)
119.4(5)
115(3)
121(5)
122(5)
N19C1C13
C2C1C13
C1C2C3
113.7(4)
126.9(5)
127.6(5)
114.1(4)
125.7(5)
116(5)
122(5)
123(5)
114(5)
121(5)
N4C3N11
N4C3C2
in comparison with the μcalc and μtheor
.
N11C3C2
N4C5C6
N4C5C10
C6C5C10
C5C6C7
C6C7C8
C7C8C9
120.2(5)
129.9(5)
110.3(5)
C10C9H9
N11C12H121
N11C12H122
N11C12H123
H121C12H122
H121C12H123
H122C12H123
122(5)
102(4)
109(5)
Note that for both compounds a considerable
exaltation between experimental and calculated using
vector-additive scheme dipole moments (both E- and
Z-isomers) is observed. For the isomers of compound I
it equals 1.13 and 3.44 D, respectively, for II, 3.12 and
2.54 D. Hence, the clear conclusion in favor of either
isomer of compound I is unfortunately impossible
from the dipole moments only. Such exaltation
indicates the presence of electron density transfer in
the unsaturated system in the direction of electron-
acceptor nitro groups. The moments of interaction
calculated as the vector magnitudes at the direction
from the benzimidazole ring to the nitro groups for
compound I are equal to 3.16 D (μexp in dioxane 7.7 D)
in E-isomer, and 3.47 D in the Z-isomer. For
compound II the moments of interaction are,
respectively: in the E-isomer from 4.3 D (experimental
moment in benzene 5.67 D) to 3.48 D (μexp in dioxane
6.5 D), in the Z-isomer 3.63 D (benzene) and 3.4 D
(dioxane). These are quite substantial values.
119.9(5)
117.3(6)
122.1(6)
121.5(5)
108(4)
129(6)
103(6)
105(7)
C8C9C10
116.6(6)
105.8(4)
C13C14H14
119(4)
119(4)
N11C10C5
C15C14H14
N11C10C9
C5C10C9
131.6(5)
122.6(5)
120.2(5)
121.6(5)
118.2(5)
121.3(6)
121(3)
C14C15H15
C16C15H15
C15C16H16
C17C16H16
C16C17H17
C18C17H17
C17C18H18
125(5)
115(5)
124(3)
117(3)
126(5)
113(5)
119(3)
C1C13C14
C1C13C18
C14C13C18
C13C14C15
C13C18H18
group and the benzimidazole ring. The characteristics
of compound II are close to literature data [21, 22].
As for the estimates of energy, the minimum energy
for compounds I and II corresponds to the E-isomer
(Table 3). While for compound II the energy preference
of E-isomer is in agreement with the theo-retical
values of the dipole moments obtained by different
quantum-chemical methods (Table 3), the existence of
compound I as the E-isomer is surprising since in it a
substantial steric strain is expected. On the other hand,
theoretical value of the dipole moment of Z-isomer of
benzimidazole derivative I well repro-duces experi-
mental dipole moment of this compound (Table 3). To
understand this problem, we performed calculations of
the model compound, 1,2-diphenyl-ethene (III). As
expected, the minimum energy corresponds to the
trans-isomer III, while the cis-isomer is less favorable
by 20 kJ mol–1. This fact suggests that nitro group can
play an important role in reducing the energy for the E-
In addition to the above exaltation, the redistri-
bution of electron density in both compounds was
confirmed by the study of their electronic spectra. The
electronic spectrum of Z-isomer of nitroalkene I
contains a long-wavelength absorption band at λmax
337 nm (ε 37 000 l mol–1 cm–1) (Table 1). The blue
shift (15 nm) of this band compared with the similar
band in the spectrum of E-form of I [λmax 352 nm
(23000)], as well as of the simplest analog, the (E)-2-
(1-methylbenzimidazol-2-yl)-1-nitroethene [λmax 367 nm
(12000)] [6] points to the fact that at the realization of
the Z-configuration of the molecule the conjugation is
less effective due to the cis-arrangement of the nitro
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

916
ISHMAEVA et al.
Table 5. Bond lengths (Å) in molecule I according to the XRD and the quantum-chemical calculationsa
122
H
121
H
12
123
C
15
H
H
2
14
9
H
H
H
15
C
11
14
N
C
16
2
9
H
16
C
C
10
3
C
C
C
8
13
8
H
C
1
C
C
17
5
4
C
C
N
18
C
7
19
17
20
C
N
H
6
O
C
18
21
7
H
O
H
6
H
Bond
O20–N19
O21–N19
N4–C3
XRD
B3PW91/6-31G(d)
1.222 [0.004]
1.217 [0.005]
1.318 [0.003]
1.371 [0.015]
1.389 [0.026]
1.378 [0.007]
1.446 [0.016]
1.480 [0.015]
1.346 [0.014]
1.469 [0.008]
1.444 [0.014]
1.402 [0.002]
1.416 [0.017]
1.386 [0.017]
1.410 [0.012]
1.389 [0.017]
1.396 [0.009]
1.404 [0.016]
1.404 [0.014]
1.390 [0.014]
1.395 [0.005]
1.394 [0.036]
1.391 [0.000]
average [0.012]
B3LYP/6-31G(d)
1.227 [0.001]
1.222 [0.010]
1.320 [0.001]
1.375 [0.011]
1.394 [0.031]
1.383 [0.012]
1.452 [0.010]
1.486 [0.021]
1.347 [0.015]
1.472 [0.005]
1.447 [0.011]
1.403 [0.003]
1.418 [0.019]
1.389 [0.020]
1.412 [0.014]
1.392 [0.020]
1.398 [0.011]
1.407 [0.019]
1.407 [0.017]
1.392 [0.016]
1.397 [0.007]
1.396 [0.038]
1.393 [0.002]
average [0.014]
B3PW91/6-31G(d) (dimer) B3PW91/6-311++G(df,p)
1.226(8)
1.212(9)
1.321(7)
1.386(7)
1.363(7)
1.371(7)
1.462(7)
1.465(7)
1.332(8)
1.477(7)
1.458(7)
1.400(8)
1.399(7)
1.369(8)
1.223 [0.003]
1.218 [0.006]
1.319 [0.002]
1.373 [0.013]
1.388 [0.025]
1.378 [0.007]
1.445 [0.017]
1.478 [0.013]
1.346 [0.014]
1.469 [0.008]
1.443 [0.015]
1.403 [0.003]
1.417 [0.018]
1.386 [0.017]
1.410 [0.012]
1.389 [0.017]
1.396 [0.009]
1.404 [0.016]
1.404 [0.014]
1.390 [0.014]
1.395 [0.005]
1.394 [0.036]
1.391 [0.000]
average [0.012]
1.214 [0.012]
1.211 [0.001]
1.313 [0.008]
1.368 [0.018]
1.385 [0.022]
1.375 [0.004]
1.444 [0.018]
1.484 [0.019]
1.340 [0.008]
1.465 [0.012]
1.441 [0.017]
1.397 [0.003]
1.412 [0.013]
1.382 [0.013]
1.405 [0.007]
1.385 [0.013]
1.392 [0.005]
1.399 [0.011]
1.399 [0.009]
1.386 [0.010]
1.390 [0.000]
1.390 [0.032]
1.386 [0.005]
average [0.011]
N4–C5
N11–C3
N11–C10
N11–C12
N19–C1
C1–C2
C1–C13
C2–C3
C5–C6
C5–C10
C6–C7
C7–C8
C8–C9
C9–C10
C13–C14
C13–C18
C14–C15
C15–C16
C16–C17
C17–C18
1.398(10)
1.372(9)
1.387(8)
1.388(8)
1.390(8)
1.376(8)
1.390(9)
1.358(11)
1.391(8)
a In brackets the difference is shown between the calculated and experimental values, in parentheses the error of experimental determination.
isomers of compounds I and II as compared with their
Z-isomers. Unfor-tunately, it is impossible to reveal
effective con-jugation in the molecules of these
compounds based on the analysis of bond lengths: no
significant changes are observed in the bond lengths
C=C, =C–N, and =C–C< while comparing E- and Z-
isomers of compounds I and II. It should be noted that
most often reflection of conjugation on bond lengths
occurs in the presence of a strong electron-releasing
substituent in vicinal position to the nitro group, for
example, piperidino-, or p-dimethyl-amino-groups or
electron-rich heterocycles indole, pyr-role, etc. [23].
Apparently, the effect of the energy reducing in I,
as expected, is the result of a combination of electronic
and steric factors. Indeed, in the case of Z-isomers, the
nitro group is almost perpendicular to the plane of the
double bond C=C, in the case of E-isomers they are
coplanar. According to the method B3LYP/6-31G*,
the angle of rotation of cyclic fragments in the trans
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POLARITY AND STRUCTURE OF 2-(1-METHYLBENZIMIDAZOL-2-YL)-1-PHENYL-
917
Table 6. Torsion angles in molecule I by the XRD data (τ, deg)
position to the nitro group [1-methylbenzimidazol-2-yl
for I and phenyl for II] to the plane of the double bond
is less in the E-isomer compared with Z isomers (6°/1°
in I, and 26°/17° in II). On the contrary, the aromatic
ring in the cis-position to the nitro group further
deviates from the plane of the double bond (33°/65° in
I and 32°/57° in II]; for III this value is 35°), which
contributes to a substantial decrease in steric strain.
Angle
τ
Angle
τ
C3N4C5C6
180.0(6)
1.0(6)
C1C2C3N11
C1C2C3N4
–161.8(6)
21.0(10)
–1.6(6)
1.3(8)
C3N4C5N10
C5N4C3N11
C5N4C3C2
0.0(6)
N4C5C10N11
C10C5C6C7
C6C5C10C9
N4C5C10C9
C6C5C10N11
N4C5C6C7
177.4(5)
179.7(5)
–178.9(6)
1.5(6)
C12N11C10C5
C3N11C10C9
C3N11C10C5
C10N11C3N4
C12N11C3N4
C10N11C3C2
C12N11C3C2
C12N11C10C9
O21N19C1C13
O20N19C1C13
O20N19C1C2
O21N19C1C2
C2C1C13C14
N19C1C13C18
N19C1C2C3
C13C1C2C3
C2C1C13C18
N19C1C13C14
–0.4(8)
178.8(5)
179.3(5)
–177.6(6)
–1.5(10)
0.7(11)
0.3(10)
–0.5(9)
180.0(6)
178.3(6)
1.3(9)
X-ray diffraction analysis of (Z)-2-(1-methylbenz-
imidazol-2-yl)-1-nitro-1-phenylethyl I indicates that
this nitroalkene molecule in the crystal also has Z-con-
figuration (Fig. 5). Tables 4–6 show the bond lengths,
bond and torsion angles in the molecule of compounds
I. Nitro group is substantially removed from the plane
of the double bond: the torsion angles are O20N19C1C2
75.9(7)° and O21N19C1C2 105.5(6)°. The benzimida-
zole heterocycle is much less turned: angle C1C2C3N is
4 21.0(10)° and C1C2C3N11 is 161.8 (6)°. The rotation
of the phenyl substituent is characterized by the torsion
angles N19C1C13C18 25.9(8)° and C2C1C13C14 26.1(9)°.
–1.0(6)
–179.1(5)
–178.5(5)
3.4(8)
C5C6C7C8
C6C7C8C9
C7C8C9C10
C8C9C10C5
C8C9C10N11
C1C13C18C17
C18C13C14C15
C1C13C14C15
C14C13C18C17
C13C14C15C16
C14C15C16C17
C15C16C17C18
C16C17C18C13
–0.7(10)
73.8(7)
–104.9(6)
75.9(7)
–105.5(6)
26.1(9)
–179.6(6)
–2.6(9)
0.2(11)
–0.4(11)
–1.0(11)
2.5(11)
25.9(8)
Figures 6 and 7 show interactions and packing of
the molecules in the crystal of compound I. The crystal
packing can be described as stacking, the molecules in
the stacks are arranged parallel. Between the layers
there are C–H···O interactions involving hydrogen atom
of benzimidazole ring and oxygen atom of the nitro group.
4.7(9)
–174.5(5)
–154.9(6)
–153.1(5)
dioxa-6-aza-cycloethanes), indicating that the
configuration (or conformation), in crystal is not
necessarily retained in solution [24].
Consequently, the results of the performed experi-
ment indicate the existence of 2-(1-methylbenz-
imidazol-2-yl)-1-nitro-1-phenylethene I in solution and
in solid phase as a Z-isomer. On the other hand, the
correctness of the results of quantum-chemical calcula-
tions carried out by different methods and pointing to
the minimum energy in the gas phase for the E-isomer,
is also doubtless. By the way, in the synthesis this
compound is formed preferably in the E-forms. There
is a dual situation: on the one hand all the used physi-
cal methods confirm the Z-structure, on the other hand,
a minimum of energy corresponds to the E-isomer.
Obviously, in the case of I the estimated value of
the minimum energy for the E-isomer does not prove
that just the E-isomer must exist. However, this
problem certainly requires further detailed study.
Thus, as a result of a complex study performed (1H
and 13C NMR and electronic spectroscopy, dipole
moments, XRD analysis, and quantum-chemical
calculations) the fine structure of substituted
nitroethenes, 2-(1-methylbenzimidazol-2-yl)-1-phenyl-
and 1,2-diphenyl-1-nitroethenes was studied, the
polarity was revealed, the geometry was determined,
and for the benzimidazole derivative the conforma-
tional features were analyzed in the arrangement of the
substituents at the carbon–carbon double bond.
In this regard, we can assume that this is a rare case
of contribution of additional interactions in the
preferred geometry of compound I that occur with the
participation of the solvent or at the formation of
crystal packing. In contrast to compound II, in the
molecule (and in the crystal) of compound I the
nitrogen atoms of the benzimidazole ring may play a
certain role. It should be noted that the literature
contains scarce data on the difference in the spatial
structure of compounds in the crystal and solution (in
particular, an example is 2-sila- and 2-phospha-1,3-
EXPERIMENTAL
1
1
1H, 13C–{1H}, H–13C HMQC, and H–13C HMBC
NMR spectra were obtained on a Jeol ECX400A
spectrometer [400 MHz (1H), 100 MHz (13C)].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

918
ISHMAEVA et al.
Fig. 5. Geometry of the molecule I in crystal.
Fig. 6. C–H···O interactions in crystals of I.
Chloroform-d1 was used as a solvent, the signal of
residual protons of the solvent were used as internal
reference. The electron absorption spectra were re-
corded on a Shimadzu UV2401PC spectrophotometer
using quartz cells, solvent acetonitrile.
Quantum-chemical calculations by HF [14] and
hybrid DFT methods B3LYP and B3PW91 [15–17]
were performed using the 6-31G(d) and 6-311++G(df, p)
basis sets (Table 3) with the Gaussian 03 software
[18]. The correspondence of the found stationary
points to the minima was proved by calculation of
second derivatives. In all cases the ownvalues of the
Hessian matrix were positive.
To determine the experimental values of dipole
moments the second Debye method was applied,
which is based on measuring the dielectric permeability
of dilute solutions of substances in a nonpolar solvent
[25]. The solvent for measuring dielectric permeability of
solutions of I was dioxane, for compound II benzene
and dioxane. Measurements were carried out at 25°C
on a BI-870 instrument (Brookhaven Instruments
Corporation), the accuracy was ±0.01. The coefficients
of equations for the calculations and the orientational
polarization are listed in Table 2. The refractive
indices of solutions were determined on a RA-500
refractometer (Kyoto Electronics), the accuracy was
±0.0001.
The calculations were performed in the Kazan
branch of the Joint Supercomputer Center of Russian
Academy of Sciences ( http://wt.knc.ru).
XRD analysis of a single crystal of compound I
was performed at the Department of diffraction of the
Multiple-access Center for collective use at the
Laboratory of diffraction research methods in the
Arbuzov Institute of Kasan Scientific Center of
Russian Academy of Sciences.
Crystals of I were obtained by crystallization from
acetone. Composition C16H13N3O2, M 279.29, mono-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 5 2012

POLARITY AND STRUCTURE OF 2-(1-METHYLBENZIMIDAZOL-2-YL)-1-PHENYL-
919
Fig. 7. Packing of molecules of I in the crystal.
clinic. At 20°C, a = 7.469(5), b = 6.566(4), c = 27.92(2) Å,
β = 94.500(8)°, V = 1364(2) Å3, dcalc = 1,359 g cm–3,
Z = 4, space group P21/c.
20.2 ml of ice water were added and the stirring was
continued for 2 h. The precipitate formed was filtered
off, washed on the filter with water, alcohol, and ether,
and dried in air. The substance I was obtained as a
mixture of isomers, E:Z = 5:1. Yield 0.9 g (87%), mp
155–157°C. The mixture of isomers was recrystallized
from 50 ml of methanol. At a short-term boiling the
methanolic solution in the process of recrystallization
E–Z isomerization occurred. Yield of I-Z isomer 0.86
g (83%), mp 210–212°C (from methanol).
The cell parameters and intensities of 10202 reflec-
tions, of which 2723 were independent with I ≥ 2σ
(Rint = 0.0603) were measured on a Bruker Smart Apex
II CCD automatic diffractometer (MoKα radiation,
graphite monochromator, λ = 0.71073 Å, ω-scanning,
measuring range: –9 ≤ h ≤ 9, –8 ≤ k ≤ 8, –34 ≤ l ≤ 34,
2.20° ≤ θ ≤ 26.00°). The extinction was accounted for
semiempirically using the SADABS software [26]
(μCu = 0.93 cm–1). The structure was solved by the
direct method and refined by least-squares method
initially in isotropic, then in anisotropic approximation
(for all non-hydrogen atoms), using the SHELXTL
[27] and WinGX [28] software. The hydrogen atoms
were revealed from the difference series of electron
density and refined isotropically. The final values of
divergence factors are: R = 0.1071, Rw = 0.2905 for
2723 independent reflections with F2 ≥ 4σ, GOOF =
1.108, number of refined parameters 244. Collection,
indexing, and data processing were performed with the
APEX2 software [29]. Analysis of intermolecular
interactions of molecules and figures were made using
the PLATON software [30]. The coordinates of atoms
of the structure and their temperature parameters are
deposited in the Cambridge database of crystal data.
1,2-Diphenyl-1-nitroethene II. The reaction mix-
ture consisting of 2 ml of methanol, 5.6 ml phenyl-
nitromethane, 0.23 g of methylamine hydrochloride,
0.07 g of sodium hydrogen carbonate, and 4.8 ml of
benzaldehyde, was stirred at 18–20°C for 72 h. The
resulting precipitate was filtered off and washed on the
filter with methanol. Yield of II 7.5 g (70%), mp 74–
75°C (from methanol). (published mp 74–75°C [9]).
ACKNOWLEDGMENTS
This work was performed under the financial
support by the Russian Foundation for Basic Research
(grant no. 10-03-00098) and the Government of St.
Petersburg (grant no. 2.5/07–06/039, PSP no. 10517).
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