Conformational study of 2-arylazo-1-vinylpyrroles

Article abstract of DOI:10.1002/mrc.1934

Conformational study of 2-phenylazo-1-vinylpyrrole and 2-(4-bromophenyl) azo-5-methyl-1-vinylpyrrole was performed on the basis of the experimental measurements and high-level ab initio calculations of their ¹³C- ¹³C and ¹³

Full text of DOI:10.1002/mrc.1934

MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2007; 45: 142–151
Published online 3 December 2006 in Wiley InterScience
(
www.interscience.wiley.com) DOI: 10.1002/mrc.1934
Conformational study of 2-arylazo-1-vinylpyrroles
1
1∗
1
1
Yury Yu. Rusakov, Leonid B. Krivdin, Elena Yu. Senotrusova, Elena Yu. Schmidt,
1
1
1
2
Alexander M. Vasiltsov, Albina I. Mikhaleva, Boris A. Trofimov, Oleg A. Dyachenko,
Anatolii N. Chekhlov and Olga N. Kazheva
2
2
1
A. E. Favorsky Institute of Chemistry, Irkutsk, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, 664033 Irkutsk, Russia
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Semenov St. 1, 142432 Chernogolovka, Moscow District, Russia
2
Received 26 September 2006; Revised 24 October 2006; Accepted 26 October 2006
Conformational study of 2-phenylazo-1-vinylpyrrole and 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole
was performed on the basis of the experimental measurements and high-level ab initio calculations of
1
3
13
13
1
their C– C and C– H spin–spin coupling constants, showing marked stereochemical behaviour upon
the internal rotation of the vinyl group and the pyrrolyl moiety. In liquid phase, both compounds were
found to adopt predominant s-trans-s-trans conformation with the noticeable population (ca. 30%) of
the higher-energy s-cis-s-trans conformation in the latter compound. As follows from the X-ray data,
2
-phenylazo-1-vinylpyrrole crystallizes in s-trans-s-trans conformation while the crystalline molecular
structure of 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole is s-cis-s-trans. Copyright  2006 John Wiley
Sons, Ltd.
&
KEYWORDS: NMR; 13C NMR; X ray; spin–spin coupling constant; lone-pair effect; SOPPA; conformational analysis;
-arylazo-1-vinylpyrroles
2
INTRODUCTION
R2
R2
+
-
H
+ +
R3
R3
R1
N2
N
Aryl- and hetarylazopyrrole dyes have been attracting
much attention over the past decade owing to their
rapidly increasing role in the design of advanced polymer
materials and chemical optoelectronic devices possessing
R1
N
N
N
CH=CH2
CH=CH2
R1 = H, Alk, Ar, 2-furyl, 2-thienyl; R = H; R , R = (CH ) ; R = H, OAlk, NO , Br.
2
1
2
2
4
3
2
1
conducting and non-linear optical properties. In spite of
Scheme 1. Synthesis of 2-arylazo-1-vinylpyrroles.
recent spectacular strides in the chemistry and applications
of azopyrrolic dyes, very little is known about their vinyl
congeners. Meanwhile, the vinyl substituent could multiply
the potential of these compounds, imparting them diverse
multi-faceted extra reactivity including polymerizability. A
limited but important family of such compounds is the
long-known azo coupled bile pigments (serum bilirubin and
In the present communication, a detailed conformational
study of the two representative compounds from this series,
2
5
-phenylazo-1-vinylpyrrole (1) and 2-(4-bromophenyl)azo-
-methyl-1-vinylpyrrole (2), has been performed on the basis
of the experimental measurements and high-level ab initio
1
3
13
13
1
calculations of their C– C and C– H spin–spin coupling
constants.
2
related species). As a measure of their importance, the
synthesis of bilirubin-based C-vinyl arylazopyrroles helped
to elucidate the mechanism of anti-oxidation by bilirubin
and its metabolites as well as their important role as anti-
4
3
3
5
2
oxidants in controlling various oxidative stresses in humans.
N
Apart from this rather specific class of arylazo vinylpyrroles,
to the best of our knowledge, no similar dyes with vinyl
substituent in the pyrrole ring, especially at the nitrogen
R1
N
N
α
β
4
H
B
R2
atom, were known prior to the very recent publication by
HX
some of us reporting the synthesis of a representative series
of 2-arylazo-1-vinylpyrroles through the azo coupling of the
corresponding 1-vinylpyrroles with arenediazonium salts
HA
R1 = R = H (1); R = CH , R = Br (2).
2
1
2
(
Scheme 1).
3
Ł
RESULTS AND DISCUSSION
Correspondence to: Leonid B. Krivdin, A. E. Favorsky Institute of
Chemistry, Irkutsk, Siberian Branch of the Russian Academy of
Sciences, Favorsky St. 1, 664033 Irkutsk, Russia.
E-mail: krivdin office@irioch.irk.ru
˛
Internal rotation of the vinyl group around the C –N bond
2
and that of the pyrrolyl moiety around the C –N bond
Copyright  2006 John Wiley & Sons, Ltd.

Conformational study of 2-arylazo-1-vinylpyrroles
143
H C
3
N
N
N
N
N
N
s-cis-s-cis
s-cis-s-cis
Br
N
N
H C
N
3
N
N
N
Br
s-cis-s-trans
s-cis-s-trans
H C
N
N
N
3
N
N
N
s-trans-s-cis
s-trans-s-cis
Br
N
N
N
N
H C
3
N
N
Br
s-trans-s-trans
s-trans-s-trans
Scheme 2. Possible rotational conformations of 2-phenylazo-1-vinylpyrrole (1) and 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole
2).
(
in 2-arylazo-1-vinylpyrroles result in four possible rotational
conformations of 1 and 2, namely, s-trans-s-trans, s-trans-s-cis,
s-cis-s-trans, and s-cis-s-cis (Scheme 2). As follows from the
As evident from the determined X-ray molecular struc-
tures of 1 and 2 (Fig. 4), the azo group in both compounds has
E-configuration, as expected. In azopyrrole 1, the –N N–
Ł
present MP2/6-311G calculations, of the four corresponding
moiety lies in the plane of the pyrrole and benzene rings (the
conformations, only the former three can be located as
true conformers providing no imaginary frequencies (as
confirmed by the harmonic vibrational frequency analysis).
On the other hand, all attempts to locate the fourth s-cis-
s-cis conformation as the stationary point on the rotational
potential energy surface, for both 1 and 2, proved to be
unsuccessful, resulting in the inevitable s-cis-s-cis ! s-
cis-s-trans conversion. Equilibrium structures optimized at
dihedral angles are 0.0 and 3.5°, respectively). The dihedral
angle between the vinyl group plane and the pyrrole ring
is 7.1°, with the antiperiplanar orientation to the azo group.
Thus, the whole molecule of 2-phenylazo-1-vinylpyrrole (1)
is essentially planar in crystalline state, providing the maxi-
mal conjugation and intra-molecular charge transfer through
the four interacting ꢀ-systems. In azopyrrole 2, the dihedral
angle between the azo group and the plane of the pyrrole
ring is also small, 2.4°. However, the azo group of 2 provides
Ł
the MP2/6-311G level and relative energies of the three
conformers of 1 and 2, namely, s-trans-s-trans, s-trans-s-cis,
and s-cis-s-trans, are shown in Figs 1 and 2 while the located
saddle points (transition states in the s-cis-s-cis ! s-cis-s-trans
conversion) of both 1 and 2 are presented in Fig. 3.
It is immediately obvious that both compounds, consid-
ered as isolated molecules, adopt predominant s-trans-s-trans
conformation with essential out-of-plane deviations of the
vinyl group (ca. 25° in 1 and ca. 38° in 2). On the other
hand, the second favorable conformer of 1 is s-trans-s-cis
a noticeable out-of-plane deviation with respect to the ben-
zene ring, 7.5°, while the dihedral angle between the planes
of the vinyl group and the pyrrole ring in 2 amounts to 20.6°,
which is essentially larger than that in 1. However, what
is most interesting is that in the crystalline phase of both
compounds the pyrrolyl moiety is s-trans, while the N-vinyl
group is s-trans in 1 and s-cis in 2. This is not so in the
isolated molecule of 2 adopting the predominant s-trans-s-
trans conformation, though with a noticeable population of
the second higher-energy s-cis-s-trans conformer, as follows
ꢀ
1
(
1.5 kcal mol ) while in the case of 2, it is s-cis-s-trans
ꢀ
1
Ł
with a much lower relative energy (0.5 kcal mol ). Accord-
ingly, the highest-energy third conformers of 1 and 2 are
from the present MP2/6-311G calculations (Fig. 2).
It is noteworthy that 1 and 2 show different conforma-
tional behaviour as isolated molecules and have different
stereochemical molecular structures in crystalline state. It
ꢀ
1
respectively, s-cis-s-trans (1.8 kcal mol ) and s-trans-s-cis
ꢀ
1
(
1.2 kcal mol ).
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc

144
Y. Y. Rusakov et al.
Figure 2. Rotational conformers of 2-(4-bromophenyl)azo-
Ł
5
-methyl-1-vinylpyrrole (2) optimized at the MP2/6-311G level
Figure 1. Rotational conformers of 2-phenylazo-1-vinylpyrrole
Ł
(relative energies are given in parentheses). Element colours:
carbon, yellow; nitrogen, cyan; bromine, red; hydrogen, grey.
(
1) optimized at the MP2/6-311G level (relative energies are
given in parentheses). Element colours: carbon, yellow;
nitrogen, cyan; hydrogen, grey.
high-level ab initio SOPPA-based calculations of J(C, C)
and J(C, H) spin–spin couplings in a number of organic
was thus a rewarding goal to perform conformational anal-
ysis of 1 and 2 in liquid phase on the basis of the NMR
data substantiated by the high-level ab initio calculations of
spin–spin coupling constants, providing important stereo-
chemical information on their structure.
1
0
11
molecules including polycycloalkanes, azomethines, five-
1
2
13,14
and six-membered heterocycles, and other compounds
demonstrated their high reliability and growing perspec-
tives in stereochemical studies, which encouraged us to use
SOPPA in the present paper.
Calculated J(C, C) and J(C, H) couplings in s-trans-s-trans,
s-trans-s-cis, and s-cis-s-trans conformers of 1 and 2 together
To study conformational behaviour of 1 and 2, we
performed experimental measurements together with theo-
retical calculations of J(C, C) and J(C, H) spin–spin coupling
constants showing marked stereochemical dependence upon
3
with their experimental values measured in CDCl solutions
˛
2
the internal rotation around the C –N and C –N bonds.
Carbon–carbon coupling constants were measured from the
INADEQUATE spectra while carbon–hydrogen couplings
were measured and unambiguously assigned by the HSQC
and HMBC experiments, as illustrated in Figs 5 and 6. The
calculations of spin–spin couplings in different conforma-
tions of 1 and 2 were performed at the Second Order Polariza-
are presented in Table 1. It follows that calculated total
values of all couplings in s-trans-s-trans conformer of both
compounds are in very good agreement with the experiment.
The FC contribution dominates in all cases; however, the
non-contact PSO contribution dramatically improves this
1
agreement in the case of all J(C, C) couplings, and hence it
should be taken into account without fail.
5
tion Propagator Approach (SOPPA) level taking into account
It is noteworthy that this agreement goes from bad
to worse when taking into consideration the other two
conformers, s-trans-s-cis and s-cis-s-trans. Indeed, this is
clearly seen when comparing the most critical couplings
showing marked stereochemical dependence in the different
all four coupling contributions, namely, Fermi contact (JFC),
spin-dipolar (JSD), diamagnetic spin-orbital (JDSO), and para-
magnetic spin-orbital (JPSO). Correlation-consistent basis set,
6
cc-pVDZ, augmented with two core s-functions of Woon and
7
1
Dunning on coupled carbons, cc-pVDZ-Cs, was applied, as
conformations of 1 and 2. For example: JꢁC-2, C-3ꢂ D
8
described elsewhere. Coupled hydrogens were assigned
72.05 Hz in s-trans-s-trans while it is 76.88 Hz in s-trans-
9
1
accordingly with the basis set aug-cc-pVTZ-J of Sauer et al.
s-cis conformations of 1 (exptl: 72.8 Hz); JꢁC
˛
, H
X
ꢂ D
including four tight s-functions and optimized for the cal-
culations of spin–spin coupling constants. Recently, the
182.08 Hz in s-trans-s-trans while it is 174.46 Hz in s-cis-
s-trans and 188.78 Hz in s-trans-s-cis conformations of 1
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc

Conformational study of 2-arylazo-1-vinylpyrroles
145
Figure 3. Saddle points (transition states in the s-cis-s-cis ! s-cis-s-trans conversion) of 2-phenylazo-1-vinylpyrrole (1) and
Ł
2
-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole (2) located at the MP2/6-311G level using the Newton–Rafson method (relative
energies with respect to the corresponding lowest-energy predominant conformations of 1 and 2 are given in parentheses). Element
colours: carbon, yellow; nitrogen, cyan; bromine, red; hydrogen, grey.
the most straightforward and understandable dihedral angle
dependences with respect to the internal rotations around
˛
2
the C –N and C –N bonds.
1
Indeed, J(C-2, C-3) increases by ca. 10 Hz when rotating
the pyrrolyl moiety around the C –N bond while going
2
from s-trans-s-trans (ϕ D 0°) to s-trans-s-cis (ϕ D 180°)
1
conformation, Fig. 7. The increase of J(C-2, C-3) in the
region of ϕ D 0–90° is due to the decrease of the negative
azo nitrogen lone-pair contribution while further increase
1
of J(C-2, C-3) in the range of ϕ D 90–180° should be
ascribed to the increase of the positive nitrogen lone-pair
contribution to this coupling. The nature of this interesting
1
effect, providing the marked difference between J(C-2,
C-3) in s-trans-s-trans and s-trans-s-cis conformations of
1
and 2, could be accounted for by the three different
contributions, namely, those of (i) the nitrogen lone-pair, (ii)
the carbon–carbon bonds containing coupling carbons, and
(iii) the carbon inner core orbitals. The first one relates to the
direct azo nitrogen lone-pair participation in the transmission
1
of spin–spin coupling giving a positive contribution to J(C-
2
, C-3) in s-trans-s-cis and a negative one in s-trans-s-trans
conformations (primary lone-pair effect), as was found by
Barone et al. who performed the dissection of 1J(C, C)
in acetoxime into orbital contributions involving those of
the nitrogen lone-pair by applying the Natural J Coupling
15
Figure 4. ORTEP diagrams of the X-ray molecular structures of
2-phenylazo-1-vinylpyrrole (1) and
2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole (2).
1
6
(
NJC) scheme based on the Natural Localized Molecular
1
7
Orbitals (NLMO) analysis of Reed and Weinhold. On the
other hand, the second and the third contributions originate
mainly in the charge transfer from the nitrogen lone-pair
to the antibonding orbital of the adjacent carbon-carbon (or
carbon–hydrogen) bond in trans orientation to the nitrogen
(
exptl: 183.1 Hz); 1JꢁC
ˇ
, H
A
ꢂ D 163.05 Hz in s-trans-s-trans
while it is 159.36 Hz in s-cis-s-trans conformations of 1
(
while it is 167.04 Hz in s-cis-s-trans conformations of 1
(
1
exptl: 164.1 Hz); JꢁC
ˇ
, H
B
ꢂ D 158.53 Hz in s-trans-s-trans
3
18
exptl: 157.2 Hz); JꢁC-2, H
X
ꢂ D 0.71 Hz in s-trans-s-trans
lone-pair, as explained in detail by Cuevas and Juaristi.
while it is 4.59 Hz in s-cis-s-trans conformations of 1 (exp:
.1 Hz), and so on. In much the same way, analogous
This charge transfer interaction, very similar to anomeric
effect, results in the substantial lengthening of the transoid
carbon–carbon bond and hence in the negative contribution
1
convincing examples could be presented for the second
azopyrrole 2.
1
to J(C-2, C-3) in s-trans-s-trans conformer (secondary lone-
Apparently, these results indicate that both compounds, 1
and 2, adopt a predominant s-trans-s-trans conformation, and
also that this unambiguously follows from the analysis of the
dihedral angle dependences of the most characteristic J(C, C)
and J(C, H) couplings in the model structure 1 presented in
pair effect).
It is the cooperation of these different intra-molecular
interactions that results in a dramatic difference of ca
10 Hz between J(C-2, C-3) in s-trans-s-trans and s-trans-s-
1
cis conformations of 1 and 2. Comparison of the measured
1
1
Figs 7–9. It appears that spin–spin couplings J(C-2, C-3),
values of JꢁC-2, C-3ꢂ D 72.8 Hz in 1 and 71.6 Hz in 2 with
3
3
and, on the other hand, JꢁC-2, H
X
ꢂ and JꢁC-5, H
X
ꢂ, display
those displayed in Fig. 7 suggests that in both compounds
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc

146
Y. Y. Rusakov et al.
Figure 5. INADEQUATE 13C NMR spectrum of 2-phenylazo-1-vinylpyrrole (1) in CDCl3 (101.61 MHz).
the pyrrolyl moiety is in s-trans orientation to the azo group.
Indeed, according to Fig. 7, this coupling is ca 73 Hz for
the s-trans orientation of the azo group in s-trans-s-trans
conformation while it is ca. 83 Hz (¾10 Hz larger!) for the
opposite s-trans-s-cis conformation.
provide a marked dihedral angle dependence with respect
to the internal rotation of the vinyl group around the C –N
˛
bond following the respective changes in the s-characters of
the corresponding C–H bonds.
Finally, we estimated the conformational ratios of both
3
3
On the other hand, JꢁC-2, H
X
ꢂ and JꢁC-5, H
X
ꢂ couplings
azopyrroles in liquid phase (solutions in CDCl ) on the
3
demonstrate classical Karplus-type dihedral angle depen-
dence with respect to the internal rotation of the vinyl group
basis of the statistical treatment of the calculated model
dihedral angle dependences presented in Figs 7–9 and
expanded into the Fourier series by ϕ in comparison
with the corresponding experimental values of J(C, C)
and J(C, H) couplings given in Table 1. The results are
as follows: 2-phenylazo-1-vinylpyrrole (1) exists almost
entirely as the s-trans-s-trans conformer with the ¾10%
population of the higher-energy s-cis-s-trans conformer while
around the C
˛
–N bond (Fig. 8), which can be expanded into
the Fourier series, Eqns (1) and (2):
3JꢁC-2, H
ꢂ D 1.92 ꢀ 2.15 cos ϕ C 1.36 cos 2ϕ
ꢂ D 2.27 C 0.69 cos ϕ C 1.46 cos 2ϕ
ꢁ1ꢂ
ꢁ2ꢂ
X
X
3JꢁC-5, H
2
-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole (2) provides
Again, comparison of the respective experimental values
of 3JꢁC-2, H
3
a ca 70 : 30 mixture of s-trans-s-trans and s-cis-s-trans con-
formations. This finding is substantiated by the pure
theoretical energy-based conformational analysis of both
azopyrroles (Fig. 10). According to these data, 2-phenylazo-
1-vinylpyrrole (1) and 2-(4-bromophenyl)azo-5-methyl-1-
vinylpyrrole (2) exist in the equilibrium mixture of s-trans-s-
trans and s-cis-s-trans conformations in the ratios of 96 : 4
and 69 : 31, which is in very good agreement with the
ꢂ and JꢁC-5, H ꢂ given in Table 1 with the
X X
former theoretical results suggests that in both compounds
the orientation of the vinyl group is essentially s-trans. This
assertion is substantiated by the dependence of the dihedral
angle of the three one-bond carbon–hydrogen couplings
1
1
1
˛ X ˇ A ˇ B
of the vinyl group, JꢁC , H ꢂ, JꢁC , H ꢂ, and JꢁC , H ꢂ,
depicted in Fig. 9, in comparison with the corresponding
experimental data (Table 1). The latter three couplings also
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc

Conformational study of 2-arylazo-1-vinylpyrroles
147
Figure 6. 13C/ H HMBC contour plot of 2-phenylazo-1-vinylpyrrole (1) in CDCl3 used to assign JꢁC-2, HXꢂ and JꢁC-5, HXꢂ.
1
3
3
corresponding results derived from the J(C, C) and J(C,
H) experimental data.
s-trans-s-trans conformation while in contrast the crystalline
molecular structure of 2 is s-cis-s-trans.
CONCLUDING REMARKS
EXPERIMENTAL
2
5
-Phenylazo-1-vinylpyrrole (1) and 2-(4-bromophenyl)azo-
-methyl-1-vinylpyrrole (2), the representative members of
NMR measurements
1
3C NMR spectra were recorded on a Bruker AVANCE
the 2-arylazo-1-vinylpyrroles series, show different confor-
mational behaviour as isolated molecules and in solution
and have different stereochemical molecular structures in
crystalline state. Both compounds, considered as isolated
molecules, adopt a predominant s-trans-s-trans conformation
with essential out-of-plane deviations of the vinyl group
400 MHz spectrometer in a 10-mm broadband probe at 300 K
3
in CDCl with hexamethyldisiloxane as an internal standard.
Carbon–carbon coupling constants were measured from the
1
3
natural-abundance C NMR spectra (101.61 MHz) using
1
9
the INADEQUATE pulse sequence of Bax et al. adjusted
for J D 70 Hz. Settings for the INADEQUATE experiments
(
ca 25° in 1 and ca 38° in 2). On the other hand, the sec-
were as follows: 90° pulse length, 12–14 µs; spectral width,
ꢀ
1
ond favorable conformer of 1 is s-trans-s-cis (1.5 kcal mol
)
10–15 kHz; acquisition time, 4–6 s; relaxation delay, 6–10 s;
characteristic delay ꢃ D 1/4J, 3.6 ms; digital resolution
0.05–0.1 Hz per pt; accumulation time, 12 h. One-bond
carbon–hydrogen coupling constants were measured from
while in the case of 2, it is s-cis-s-trans with a much lower rela-
ꢀ
1
tive energy (0.5 kcal mol ). Accordingly, the highest-energy
third conformers of 1 and 2 are, respectively, s-cis-s-trans
ꢀ
1
ꢀ1
13
(
1.8 kcal mol ) and s-trans-s-cis (1.2 kcal mol ). In liquid
the proton-coupled C NMR spectra (101.61 MHz) using the
phase, both compounds adopt predominant s-trans-s-trans
conformation with considerable population (ca 30%) of the
second s-cis-s-trans conformation in 2, as follows from the
experimental measurements together with theoretical calcu-
lations of J(C, C) and J(C, H) spin–spin coupling constants
providing marked stereochemical dependences upon the
internal rotation around the C –N and C –N bonds in 2-
arylazo-1-vinylpyrroles. This result is in line with the pure
theoretical energy-based conformational analysis of both
azopyrroles. On the basis of the X-ray data, 1 crystallizes in
same spectral widths, acquisition times, relaxation delays,
and digital resolutions as in the INADEQUATE experiments,
and their assignment was confirmed by the C/ H HSQC
1
3
1
spectra. Vicinal carbon–hydrogen coupling constants were
1
3
1
measured from the C/ H HMBC spectra acquired with
64 ð 8 k complex points in t
1 2
and t for spectral widths of
˛
2
13
1
5000 Hz in t
1
ꢁ Cꢂ and 500 Hz in t
2
ꢁ Hꢂ using the following
settings: acquisition time, 4 s; relaxation delay, 6 s; digital
1
3
1
resolution, 0.1 Hz per pt in F1 ( C) and 0.05 Hz in F2 ( H);
total acquisition time, 4 h.
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc

148
Y. Y. Rusakov et al.
Table 1. Spin-spin coupling constants 13C–13C and 13C– H of 1 and 2 calculated at the SOPPA level in comparison with
1
experimental valuesa
Cmpd.
Conformer
Coupling constant
JDSO
JPSO
JSD
JFC
J
Exp.
1
1
s-trans-s-trans
J(C-2, C-3)
J(C-3, C-4)
J(C-4, C-5)
JꢁC˛, Cˇꢂ
JꢁC˛, HXꢂ
JꢁCˇ, HAꢂ
0.32
0.24
0.25
0.17
0.97
0.56
0.63
0.15
ꢀ0.47
0.32
0.24
0.25
0.18
0.95
0.58
0.66
ꢀ0.40
0.14
0.31
0.24
0.25
0.18
0.98
0.57
0.64
0.07
ꢀ0.40
0.33
0.25
0.29
0.19
1.00
0.59
0.68
0.16
ꢀ0.38
0.33
0.25
0.29
0.18
1.02
0.59
0.68
ꢀ0.36
0.14
0.32
0.25
0.29
0.19
1.02
0.60
0.69
0.09
ꢀ6.03
ꢀ4.97
ꢀ6.14
ꢀ8.20
ꢀ0.11
0.43
0.41
ꢀ0.25
0.22
ꢀ6.08
ꢀ4.97
ꢀ6.12
ꢀ8.23
0.05
1.72
0.78
1.42
3.33
0.22
0.22
0.22
0.00
0.00
1.71
0.78
1.41
3.39
0.13
0.20
0.29
ꢀ0.01
0.01
1.54
0.75
1.41
3.36
0.29
0.22
0.22
0.02
ꢀ0.05
1.70
0.74
1.33
3.27
0.23
0.22
0.24
0.00
ꢀ0.01
1.70
0.71
1.33
3.32
0.25
0.22
0.23
ꢀ0.01
0.01
1.52
0.72
1.33
3.39
0.28
0.22
0.22
0.02
ꢀ0.04
76.04
63.40
69.78
83.75
181.00
161.84
157.27
0.81
72.05
59.45
65.31
79.05
182.08
163.05
158.53
0.71
72.8
1
– b
1
64.1
77.6
183.1
164.1
157.2
1.1
1
1
1
1JꢁCˇ, HBꢂ
3
JꢁC-2, HXꢂ
JꢁC-5, HXꢂ
J(C-2, C-3)
J(C-3, C-4)
J(C-4, C-5)
JꢁC˛, Cˇꢂ
JꢁC˛, HXꢂ
JꢁCˇ, HAꢂ
3
4.53
4.28
4.7
1
s-cis-s-trans
s-trans-s-cis
s-trans-s-trans
s-cis-s-trans
s-trans-s-cis
75.76
63.21
69.86
84.03
173.33
158.18
165.92
4.82
71.71
59.26
65.4
79.37
174.46
159.36
167.04
4.59
1
1
1
1
1
0.40
0.17
0.18
1JꢁCˇ, HBꢂ
3
JꢁC-2, HXꢂ
JꢁC-5, HXꢂ
J(C-2, C-3)
J(C-3, C-4)
J(C-4, C-5)
JꢁC˛, Cˇꢂ
JꢁC˛, HXꢂ
JꢁCˇ, HAꢂ
3
ꢀ0.22
ꢀ6.02
ꢀ4.92
ꢀ6.20
ꢀ8.36
ꢀ0.21
0.38
0.34
ꢀ0.15
0.19
ꢀ5.98
ꢀ4.98
ꢀ6.20
ꢀ8.31
ꢀ0.12
0.36
0.27
ꢀ0.24
0.17
ꢀ6.08
ꢀ5.02
ꢀ6.19
ꢀ8.42
0.01
0.32
0.11
0.17
3.03
2.96
1
81.05
63.51
68.95
82.83
187.72
160.57
157.86
ꢀ0.22
3.84
75.07
63.18
69.64
82.55
180.39
159.91
158.37
0.63
76.88
59.58
64.41
78.01
188.78
161.74
159.06
ꢀ0.28
3.58
71.12
59.19
65.06
77.7
1
1
1
1
1
1JꢁCˇ, HBꢂ
3
JꢁC-2, HXꢂ
JꢁC-5, HXꢂ
J(C-2, C-3)
J(C-3, C-4)
J(C-4, C-5)
JꢁC˛, Cˇꢂ
JꢁC˛, HXꢂ
JꢁCˇ, HAꢂ
3
1
2
71.6
– b
1
1
64.4
77.3
178.7
160.9
160.9
2.3
1
1
181.5
161.08
159.56
0.55
1
1JꢁCˇ, HBꢂ
3
JꢁC-2, HXꢂ
JꢁC-5, HXꢂ
J(C-2, C-3)
J(C-3, C-4)
J(C-4, C-5)
JꢁC˛, Cˇꢂ
JꢁC˛, HXꢂ
JꢁCˇ, HAꢂ
3
4.47
4.25
3.9
1
74.82
63.29
69.58
83.04
173.77
158.16
164.63
4.12
70.77
59.23
65.01
78.12
175.05
159.29
165.65
3.92
1
1
1
1
1
1JꢁCˇ, HBꢂ
3
JꢁC-2, HXꢂ
3
JꢁC-5, HXꢂ
ꢀ0.22
ꢀ5.98
ꢀ4.92
ꢀ6.25
ꢀ8.48
ꢀ0.21
0.32
0.25
ꢀ0.13
0.13
1.87
1.80
1
1
J(C-2, C-3) J(C-3, C-4)
80.05
63.13
69.25
82.87
186.55
159.40
157.83
ꢀ0.24
3.54
75.91
59.18
64.62
77.97
187.64
160.54
158.99
ꢀ0.26
3.33
1
J(C-4, C-5)
JꢁC˛, Cˇꢂ
JꢁC˛, HXꢂ
JꢁCˇ, HAꢂ
1
1
1
1JꢁCˇ, HBꢂ
3
JꢁC-2, HXꢂ
JꢁC-5, HXꢂ
3
ꢀ0.30
a
All couplings and coupling contributions are in Hz.
Not measured owing to signal overlapping.
b
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc

Conformational study of 2-arylazo-1-vinylpyrroles
149
1
Figure 7. Dihedral angle dependence of J(C-2, C-3) in
2-phenylazo-1-vinylpyrrole (1) calculated at the SOPPA level.
1
Figure 9. Dihedral angle dependences of JꢁC˛, HXꢂ,
1
1
JꢁCˇ, HAꢂ, and JꢁCˇ, HBꢂ in 2-phenylazo-1-vinylpyrrole (1)
calculated at the SOPPA level.
synthesis, the non-hydrogen atoms were refined anisotropi-
3
Figure 8. Dihedral angle dependences of JꢁC-2, HXꢂ and
2
cally by the full-matrix procedure on F using the SHELXL-97
3
JꢁC-5, HXꢂ in 2-phenylazo-1-vinylpyrrole (1) calculated at the
24
package. Hydrogen atoms were found experimentally and
SOPPA level.
refined isotropically.
Computational details
Geometric optimizations were performed with the GAMESS
Synthesis
2
0
21
Ł
code, at the MP2 level, using the 6-311G basis set of
Both azopyrroles, 1 and 2, were prepared according to the
following general procedure. To a 0 C solution of aromatic
amine (10 mmol) and aqueous HCl (3 ml) in water 15 (ml),
2
2
°
Pople and coworkers without symmetry constraints, i.e.
assuming the C symmetry point group. Calculations of
spin–spin coupling constants have been carried out using the
1
a 0
°
C solution of NaNO (0.69 g, 10 mmol) in water (10 ml)
2
2
3
5
°
DALTON package at the SOPPA level with the correlation-
was added and the mixture was stirred at 0 C for 0.5 h. The
6
,7
consistent basis sets of Dunning and coworkers and Sauer
resulting diazonium salt solution was neutralized (pH ¾7)
9
23
et al., either taken from the Dalton Basis Sets Library
3
with dry NaHCO (3.0 g, 36 mmol). After stirring for 10 min,
the solution obtained was poured into a 0 C solution of 1-
vinylpyrrole (10 mmol) in ethanol (10 ml). The mixture was
stirred at 0 °C for 2 h. The precipitate was filtered off and
dried in vacuo. In cases when the solid did not precipitate, the
°
without modifications or slightly modified by adding or
removing polarization, core, and tight or diffuse functions,
8
1
as specified elsewhere. The SOPPA calculations of J(C, C)
1
and J(C, H) were performed within the C
1
point group as
well, and all compounds were adopted in their equilibrium
conformations located at the MP2/6-311G level.
reaction mixture was extracted with Et O ꢁ15 ð 3 mlꢂ. The
2
Ł
extract was dried with K CO and distilled off. The products
2
3
2 3
were purified by column chromatography (Al O , eluent – n-
X-ray experiments
The X-ray diffraction data were collected on an Enraf-Nonius
CAD-4 diffractometer with graphite-monochromatized Mo-
K˛ radiation at room temperature (ω2Â -scanning). Crys-
hexane) or recrystalization from n-hexane. Upon storage of
the azo coupling products, 1 and 2, at ambient temperature
for several months, neither changes in their UV/vis spectra
ꢀ
1
1
nor appearance of redundant signals in their H NMR spectra
talline structures were solved by direct methods and Fourier
were observed, which evidences their stability.
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc

150
Y. Y. Rusakov et al.
Figure 10. Dihedral angle dependence of the relative energies (a), (b) and statistical distribution of the rotational conformations (c),
Ł
(
d) of 1 and 2 calculated at the MP2/6-311G level.
2
-Phenylazo-1-vinylpyrrole (1)
Acknowledgements
1
Crimson crystals, mp 72–74 °C. H NMR ꢁCDCl
ꢂ υ: 7.88 (m,
Financial support from Russian Foundation for Basic Research
(Grant No. 05-03-32231) is acknowledged.
3
3
3
2
(
H
H, H
m, 2H, H
), 6.45 (m, 1H, H
NMR ꢁCDCl ꢂ υ: 153.46 (C
), 129.07 (C ), 122.33 (C
3 (C-3), 99.66 (C ). IR (KBr, ꢄmax cm ): 3165–3105, 1630,
535, 1501, 1475, 1450, 1410, 1360, 1345, 1305, 1280, 1230,
180, 1125, 1045, 1005, 955, 905, 880, 800, 765, 710, 675, 650,
80, 550, 500, 450. Calcd (%): C, 73.07; H, 5.62; N 21.30. Found
o
), 7.87 (dd, 1H, H
), 7.43 (m, 1H, H
), 5.38 (d, 1H, H
X
, JB–X 16.0 Hz, JA–X 8.8 Hz), 7.52
m
p
), 7.36 (m, 1H, H
5
), 6.79 (m, 1H,
1
3
3
4
B
A
,), 4.97 (d, 1H, H ). C
REFERENCES
3
i
), 145.73 (C-2), 129.97 (C
p
), 129.84
1
. (a) Yokomichi N, Seki K, Tada S, Yamabe T. Synth. Met. 1995; 69:
77; (b) Zotti G, Zecchin S, Schiavon G, Berlin A, Pagani GA,
Canavesi A, Casalbore-Miceli G. Synth. Met. 1996; 78: 51;
c) Chyla A, Kucharski S, Sworakowski J, Bie n´ kovski M. Thin
(
C
˛
m
o
), 120.73 (C-5), 112.14 (C-4), 100.
5
ꢀ
1
0
1
1
5
ˇ
(
Solid Films 1996; 284–285: 496; (d) Nero JD, Laks D. Synth.
Met. 1999; 101: 440; (e) Zhu Z, Wang Y, Lu Y. Macromolecules
2003; 36: 9585; (f) Wagner-Wysiecka E, Luboch E, Kowalczyk M,
(
11 3
%): C, 73.24; H, 5.70; N 21.17. C12H N .
Biernat JF. Tetrahedron 2003; 59: 4415; (g) Facchetti A, Abbotti A,
Beverina L, van der Boom ME, Dutta P, Evmenenko G,
Marks TJ, Pagani GA. Chem. Mater. 2002; 14: 4996; (h) Wang Y,
Ma J, Jiang Y. J. Phys. Chem. A 2005; 109: 7197.
2
-(4-Bromophenyl)azo-5-methyl-1-vinylpyrrole (2)
1
Orange needles, mp 72–74 °C. H NMR ꢁCDCl
ꢂ υ: 7.62 (d,
3
2. Heirwegh KPM, van Hees GP, Leroy P, van Roy FP, Jansen FH.
3
3
2
1
1
H, H
o
, Joꢀm 8.8 Hz), 7.53 (d, 2H, H
m
), 7.31 (dd, 1H, H
X
, JB–X
Biochem. J. 1970; 120: 877.
3. Yamaguchi T, Shhiji I, Sugimoto A, Komoda Y, Nakajima H.
Biochim. Biophys. Acta 1996; 1289: 110.
3
3
6.1 Hz, JA–X 9.3 Hz), 6.71 (d, 1H, H
3
, J3–4 3.9 Hz), 6.13 (d,
H, H
4
), 5.40 (d, 1H, H
B
), 5.16 (d, 1H, H
A
), 2.41 (s, 3H, Me).
), 147.01 (C-2), 135.53 (C-5),
), 123.01 (C ), 112.09 (C-4),
), 100.93 (C-3), 14.55 (Me). IR (KBr, ꢄmax cm ):
4
. Trofimov BA, Schmidt EYu, Mikhaleva AI, Vasiltsov AM,
Zaitsev AB, Smolyanina NS, Senotrusova EYu, Afonin AV,
Ushakov IA, Petrushenko KB, Kazheva ON, Dyachenko OA,
Smirnov VV, Schmidt AF, Markova MV, Morozova LV. Eur. J.
Org. Chem. 2006; 17: 4021.
1
3
C NMR ꢁCDCl
32.16 (C
08.17 (C
3
ꢂ υ: 152.57 (C
i
1
1
3
1
8
5
m
), 129.55 (C
˛
), 123.58 (C
o
p
ꢀ
1
ˇ
127, 3055, 2911, 1643, 1582, 1567, 1535, 1474, 1433, 1416,
388, 1344, 1303, 1293, 1206, 1182, 1150, 1062, 1026, 1004, 960,
86, 831, 812, 783, 774, 762, 706, 510, 492, 458. Calcd (%): C,
3.81; H, 4.17; Br, 27.54; N 14.48. Found (%): C, 53.97; H, 4.09;
5. (a) Nielsen ES, Jørgensen P, Oddershede J. J. Chem. Phys. 1980;
73: 6238; (b) Packer MJ, Dalskov EK, Enevoldsen T, Jensen HJAa,
Oddershede J. J. Chem. Phys. 1996; 105: 5886; (c) Bak KL, Koch H,
Oddershede J, Christiansen O, Sauer SPA. J. Chem. Phys. 2000;
112: 4173.
3
Br, 27.51; N 14.33. C13H12BrN .
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc

Conformational study of 2-arylazo-1-vinylpyrroles
151
6
. (a) Dunning TH Jr. J. Chem. Phys. 1989; 90: 1007; (b) Kendall RA,
Dunning TH Jr, Harrison RJ. J. Chem. Phys. 1992; 96: 6796;
9193; (c) Grayson M, Sauer SPA. Mol. Phys. 2000; 98: 1981;
(d) Provasi PF, Aucar GA, Sauer SPA. Int. J. Mol. Sci. 2003; 4:
231; (e) Barone V, Provasi PF, Peralta JE, Snyder JP, Sauer SPA,
Contreras RH. J. Phys. Chem. A 2003; 107: 4748.
(c) Woon DE, Dunning TH Jr. J. Chem. Phys. 1993; 98: 1358.
7
. Woon DE, Dunning TH Jr. J. Chem. Phys. 1995; 103: 4572.
. (a) Krivdin LB, Sauer SPA, Peralta JE, Contreras RH. Magn.
Reson. Chem. 2002; 40: 187; (b) Sauer SPA, Krivdin LB. Magn.
Reson. Chem. 2004; 42: 671; (c) Krivdin LB. Magn. Reson. Chem.
8
15. Barone V, Peralta JE, Contreras RH, Sosnin AV, Krivdin LB.
Magn. Reson. Chem. 2001; 39: 600.
16. Peralta JE, Contreras RH, Snyder JP. J. Chem. Soc., Chem.
Commun. 2000; 20: 2025.
2004; 42: S168; (d) Krivdin LB. Magn. Reson. Chem. 2005; 43: 101.
9
. Provasi PF, Aucar GA, Sauer SPA. J. Chem. Phys. 2001; 115: 1324.
17. Reed AE, Curtiss LA, Weinhold F. Chem. Rev. 1988; 88: 899.
18. Cuevas G, Juaristi E. J. Am. Chem. Soc. 2002; 124: 13088.
19. Bax A, Freeman R, Kempsell SP. J. Am. Chem. Soc. 1980; 102:
4849.
1
1
0. Krivdin LB. Magn. Reson. Chem. 2005; 43: 101.
1. (a) Krivdin LB, Scherbina NA, Istomina NV. Magn. Reson. Chem.
2005; 43: 435; (b) Scherbina NA, Istomina NV, Krivdin LB.
Russ. J. Org. Chem. 2005; 41: 1103; (c) Krivdin LB, Larina LI,
Chernyshev KA, Rozentsveig IB. Magn. Reson. Chem. 2005; 43:
20. Schmidt MW, Baldridge KK, Boatz JA, Elbert ST, Gordon MS,
Jensen JH, Koseki S, Matsunaga N, Nguyen KA, Su SJ,
Windus TL, Dupuis M, Montgomery JA. J. Comput. Chem. 1993;
14: 1347.
937; (d) Krivdin LB, Nedolya NA. Tetrahedron Lett. 2005; 46:
7367; (e) Krivdin LB, Larina LI, Chernyshev KA, Rulev AYu.
Magn. Reson. Chem. 2006; 44: 178; (f) Krivdin LB, Larina LI,
Chernyshev KA, Keiko NA. Aust. J. Chem. 2006; 59: 211.
21. Møller C, Plesset MS. Phys. Rev. 1934; 46: 618.
22. Krisnan R, Binkley JS, Seeger R, Pople JA. J. Chem. Phys. 1980; 72:
12. Rusakov YuYu, Krivdin LB, Schmidt EYu, Mikhaleva AI,
Trofimov BA. Magn. Reson. Chem. 2006; 44: 692.
650.
23. A˚ gren H, Angeli C, Bak KL, Bakken V, Christiansen O, Cimi-
1
3. (a) Wiggelsworth RD, Raynes WT, Sauer SPA, Oddershede J.
Mol. Phys. 1997; 92: 77; (b) Wiggelsworth RD, Raynes WT,
Sauer SPA, Oddershede J. Mol. Phys. 1998; 94: 851; (c) Sauer SPA,
raglia R, Coriani S, Dahle P, Dalskov EK, Enevoldsen T, Fer-
nandez B, Haettig C, Hald K, Halkier A, Heiberg H, Hel-
gaker T, Hettema H, Jensen HJA, Jonsson D, Joergensen P, Kir-
pekar S, Klopper W, Kobayashi R, Koch H, Ligabue A, Lut-
naes OB, Mikkelsen KV, Norman P, Olsen J, Packer MJ, Peder-
sen TB, Rinkevicius Z, Rudberg E, Ruden TA, Ruud K, Salek P,
Sanchez de Meras A, Saue T, Sauer SPA, Schimmelpfennig B,
Sylvester-Hvid KO, Taylor PR, Vahtras O, Wilson DJ. Dalton,
A Molecular Electronic Structure Program, Release 2.0. 2005; see
http://www.kjemi.uio.no/software/dalton/dalton.html.
ˇ
Møller CK, Koch H, Paidarov a´ I, Spirko V. Chem. Phys.
998; 238: 385; (d) Wiggelsworth RD, Raynes WT, Kirpekar S,
1
Oddershede J, Sauer SPA. J. Chem. Phys. 2000; 112: 3735;
Wiggelsworth RD, Raynes WT, Kirpekar S, Oddershede J,
Sauer SPA. J. Chem. Phys. 2001; 114: 9192; (e) Sauer SPA,
Raynes WT, Nicholls RA. J. Chem. Phys. 2001; 115: 5994.
14. (a) Kirpekar S, Sauer SPA. Theor. Chem. Acc. 1999; 103:
1
3
46; (b) Sauer SPA, Raynes WT. J. Chem. Phys. 2000; 113:
121; Sauer SPA, Raynes WT. J. Chem. Phys. 2001; 114:
24. Sheldrick GM. SHELXL 97, Program for the Refinement of Crystal
Structures. University of G o¨ ttingen: G o¨ ttingen, Germany, 1997.
Copyright  2006 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2007; 45: 142–151
DOI: 10.1002/mrc