Synthesis, properties, and molecular structure of nitro-substituted N-methyl-N-nitroanilines

Article abstract of DOI:10.1134/S1070363206010142

Ten mono-, di-, and trinitro derivatives of N-methyl-N-nitroaniline were synthesized and studied by spectral, electrooptical, and quantum-chemical methods. Three of these derivatives, N-methyl-N,2,3-trinitroaniline, N-methyl-N,2,5-trinitroaniline, N-methyl-N,3,5-trinitroaniline, were also examined by the X-ray diffraction method. The N-nitroamino group in their molecules is almost planar, the N⁷-N⁸ bond is shortened, and the N⁸ atom is characterized by a strong deficit of electron density. The dihedral angle between the planes of the N-nitroamino group and the benzene ring is 56°-92°, which makes conjugation between these fragments impossible. The N-nitroamino group in the examined compounds acts as a weak electron donor with respect to the nitro groups in the aromatic ring; the mechanism of this effect is inductive. Pleiades Publishing, Inc. 2006.

Full text of DOI:10.1134/S1070363206010142

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 1, pp. 64 75.
Original Russian Text V.V. Prezhdo, A.S. Bykova, O.V. Prezhdo, Z. Daszkiewicz, J.B. Kyziol, J. Zaleski, 2006, published in Zhurnal Obshchei Khimii,
2006, Vol. 76, No. 1, pp. 69 80.
Pleiades Publishing, Inc., 2006.
Synthesis, Properties, and Molecular Structure
of Nitro-Substituted N-Methyl-N-nitroanilines
V. V. Prezhdo, A. S. Bykova, O. V. Prezhdo,
Z. Daszkiewicz, J. B. Kyziol, and J. Zaleski
Kharkov Polytechnical Institute, ul Frunze 21, Kharkov, 61002 Ukraine
Institute of Chemistry, Jan Kochanowski Technical Universitety of Kielce, Kielce, Poland
Institute of Chemistry, Technical University of Opole, Opole, Poland
G. Washington University, Seattle WA, USA
Received July 20, 2004
Abstract Ten mono-, di-, and trinitro derivatives of N-methyl-N-nitroaniline were synthesized and studied
by spectral, electrooptical, and quantum-chemical methods. Three of these derivatives, N-methyl-N,2,3-trinitro-
aniline, N-methyl-N,2,5-trinitroaniline, N-methyl-N,3,5-trinitroaniline, were also examined by the X-ray dif-
fraction method. The N-nitroamino group in their molecules is almost planar, the N7 N8 bond is shortened,
and the N8 atom is characterized by a strong deficit of electron density. The dihedral angle between the planes
of the N-nitroamino group and the benzene ring is 56 92 , which makes conjugation between these fragments
impossible. The N-nitroamino group in the examined compounds acts as a weak electron donor with respect to
the nitro groups in the aromatic ring; the mechanism of this effect is inductive.
DOI: 10.1134/S1070363206010142
Rearrangement of aromatic N-nitro amines into
C-nitro compounds can be promoted be various fac-
tors, including acid catalysis. Depending on the N-
nitro amine structure, different acidities of the
medium are required. N-Methyl-N-nitroaniline (I)
undergoes such rearrangement by the action of dilute
(0.1 M) sulfuric acid solution [1], while the rearran-
gement of N-methyl-N,2,3-trinitroaniline occurs only
in concentrated (78%) sulfuric acid at room tempera-
ture [2]. The difference in the reaction conditions
originates from the presence of nitro groups in the
aromatic ring. Presumably, substituents in the aro-
matic ring and their position affect migration of the
nitro group, which should be reflected in properties of
secondary N-nitroarylamines. On the other hand, the
results of X-ray diffraction study of N-nitro amine I
and its substituted derivatives showed that -electron
system of the nitroamino group is not involved in
conjugation with the benzene ring [3, 4]. Formalisti-
cally, this means that lone electron pair on the amino
nitrogen atom is delocalized toward the nitro group
and that it does not interact with -electrons of the
ring. As a result, para-substituted N-methyl-N-nitro-
anilines are characterized by considerably lower inter-
conjugated with the aromatic ring. For example,
values for N-methyl-N,4-dinitroaniline and N,N-di-
methyl-4-nitroaniline are 0.28 [5] and 1.48 D [6],
respectively.
It was interesting to estimate the effect of introduc-
tion of nitro groups (which are strong electron accep-
tors) into the aromatic ring on charge distribution in
the molecule, specifically to elucidate whether ac-
cumulation of nitro groups in the N-methyl-N-nitro-
aniline molecule will lead to competition for lone
electron pair on the amino nitrogen atom. These ef-
fects should be reflected in the dipole moments, molar
Kerr constants, spectral parameters, and molecular
structure. Therefore, we synthesized mono-, di-, and
trinitro derivatives II IX and examined their proper-
ties (Table 1).
In the IR spectra of para-substituted derivatives of
I, absorption band due to asymmetric stretching vibra-
tions of the N-nitroamino group was located at 1520
1
1570 cm [7]. The nitro group attached to the aro-
matic ring is more sensitive to para substituent: The
corresponding absorption band appears in the region
1
1490 1579 cm , depending on the electronic proper-
action moments
=
[5] than those intrin-
ties of the other substituent [10]. In the IR spectra of
compounds II XI, absorption bands belonging to N-
nitro and C-nitro groups either overlap or
exp
sic to, e.g., para-substituted N,N-dimethylanilines in
which n-electrons on the amino nitrogen atom are
64

SYNTHESIS, PROPERTIES, AND MOLECULAR STRUCTURE
65
H3C
NO2
NHCH3
NO2
NHCH3
NO2
N
H2SO4
NO2
O2N
+
II
NO2
N
NO2
NO2
NO2
H3C
H3C
N
NO2
O2N
NO2
VIII
VI
H3C
NO2
NHCH3
N
NHCH3
NO2
NHCH3
O2N
+
H2SO4
+
NO2
NO2
NO2
NO2
III
NO2
NO2
NO2
NO2
H3C
H3C
H3C
NHCH3
N
N
N
NO2
NO2
O2N
NO2
NO2
NO2
NO2
IX
V
VII
1
are displaced by 20 30 cm with respect to each
other (Table 1).
from interaction between the para substituents, it
cannot be compared with that observed, e.g., for N,N-
dimethyl-4-nitroaniline which absorbs in the visible
region [12]. A conclusion can be drawn that the
C-nitro and N-nitroamino groups are not involved in
donor acceptor interaction with each other.
The stretching vibration frequency of C-nitro
groups ranges from 1520 to 1560 cm , indicating that
the N(CH3)NO2 group is a stronger electron acceptor
than, e.g., halogen atom [10]. Symmetric stretching
vibrations of N- and C-nitro groups have different
frequencies (1280 1300 and 1340 1350 cm , respec-
tively). It is well known [11] that N-nitro groups
absorb at lower frequencies (by about 50 cm ) than
C-nitro groups. An exception is compound XI which
shows in the IR spectrum a strong absorption band at
1315 cm , i.e., beyond the typical range. Neverthe-
less, we can conclude that the number and position of
C-nitro groups do not affect vibration frequencies of
the N-nitro group, which occupy different regions,
1
Table 2 contains the experimental dipole moments
and molar Kerr constants of compounds II XI to-
gether with those calculated according to the vector-
and tensor additive schemes. Molecules II XI are
strongly polar; the dipole moments of some com-
pounds exceed 6 D. In these cases, molecular confor-
mation is to be known to analyze intramolecular inter-
action effects. The principal structural data for
aromatic nitro compounds were obtained by the X-ray
diffraction method [13]. These data together with the
results of theoretical calculations of the energy of
intramolecular interactions indicated that the dihedral
angle between the aromatic ring plane and the nitro
group is equal to 0 provided that no ortho substi-
tuents are present [14]. Molecular conformations of
ortho-substituted nitrobenzenes are determined by
steric interactions which can be estimated on the basis
1
1
1
1
1280 1300 and 1520 1560 cm .
The electronic absorption spectra of almost all of
the examined compounds contained a strong band
(3.96 < log < 4.40) with its maximum at
250 nm. Only in the spectrum of IV the correspond-
ing maximum is displaced to the red region (
240
=
max
283 nm). Even if this weak red shift would result
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 1 2006

66
PREZHDO et al.
of their physical properties [15 17]. It is important
that sterically hindered nitroaromatic compounds
whose steric and mesomeric interaction energies are
related to each other may be conformationally labile
[15]. Presumably, electronic effects of remote substi-
tuents (if they are capable of affecting the angle of
rotation of nitro groups) should be pronounced just in
such sterically hindered molecules [15].
While studying nitro derivatives of N-methyl-N-
nitroaniline, the main problem is to elucidate intramo-
lecular interactions between functional groups in their
Table 1. Melting points and IR and UV spectra of nitro-substituted N-methyl-N-nitroanilines II XI
1
IR spectrum, , cm
UV spectrum,
max, nm ( )
Comp. no.
Substitution pattern
mp,
C
s(NO2)
as(NO2)
I
44.5
258 (2770),
265 (2070)
245 (11200)
251 (13400)
283 (9100)
239 (10600)
234 (16600)
249 (14500)
227 (18500)
252 (9200)
244 (19400)
227 (25400)
II
2-NO2
3-NO2
4-NO2
2,3-(NO2)2
2,4-(NO2)2
2,5-(NO2)2
2,6-(NO2)2
3,4-(NO2)2
3,5-(NO2)2
2,4,6-(NO2)3
65 66
1295, 1345
1292, 1351
1294, 1344
1297, 1347
1284, 1346
1303, 1346
1292, 1348
1315, 1347
1285, 1352
1286, 1351
1530
1529
1521
III
IV
V
VI
VII
VIII
IX
X
72 73a
138 140b
102 104
113 114c
162 165
111 112
97 99
1549, 1564
1522, 1540
1525, 1555
1536
1524, 1545
1544
110 111
XI
131 132d
1541, 1556
a
b
c
d
Published data, mp, C:
71 73 [7];
139 [8];
111 113 [9]; and
127 [9].
Table 2. Experimental (benzene, 25 C) and calculated by the vector and tensor additive schemes dipole moments ( )
and molar Kerr constants (mK) of nitro-substituted N-methyl-N-nitroanilines II XI
a
Comp.
no.
P2
,
PD,
,
exp
D
sK2 1014 mKexp 1012
H
H
L
cm3
131.8
452.3
373.2
1026
cm3
L
II
27.01
10.34
12.31
4.739
10.56
4.195
29.15
9.434
17.39
5.497
9.751
3.151
23.01
7.466
17.73
5.745
9.764
3.321
9.116
2.374
1.082
0.040
0.965
0.274
1.466
0.582
1.126
0.160
1.361
1.728
0.866
0.492
1.298
0.343
1.238
0.624
1.235
0.400
2.258
1.585
50.76
50.76
50.76
57.01
57.01
57.01
57.01
57.01
6.55
4.43
3.97
6.88
5.22
4.00
6.09
5.35
0.0407
0.0393
0.0435
0.0317
0.0218
0.0522
0.0354
0.0388
0.0511
0.0613
0.732
0.0523
3.280
0.269
0.171
0.159
0.644
0.229
0.365
0.573
109.6
35.46
53.42
67.75
51.19
30.70
60.24
41.95
215.8
69.85
105.2
164.0
123.9
74.29
145.8
101.5
III
IV
V
VI
VII
VIII
IX
X
614.8
384.9
816.3
641.3
350.9
352.0
57.01
25.35
61.92
3.79
61.35
3.74
XI
35.93
103.2
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SYNTHESIS, PROPERTIES, AND MOLECULAR STRUCTURE
67
Table 2. (Contd.)
b
b
Comp.
no.
,
mKcalc
1012
,
,
mK
1012
Comp.
no.
,
mKcalc
1012
,
,
mK
1012
calc
D
1
D
calc
D
1
D
D
D
II
6.60
5.11
4.18
8.18
5.11
0.45
0.20
0.28
0.79
0.70
0.45
0.20
0.28
0.40
0.35
VII
4.34
7.27
6.90
4.18
4.34
0.57
0.60
1.05
0.34
0.81
0.28
0.30
0.52
0.17
0.40
236.0
71.33
107.7
199.1
142.6
20.25
1.48
89.56
171.0
129.0
62.69
122.4
15.27
25.18
27.47
1.34
III
IV
V
VIII
IX
X
2.55
35.12
18.73
VI
XI
19.17
a
b
For definitions of
,
,
,
,
, P , P ,
, mK ,
calc
, and mK, see text. Variation of the dipole moment per one nitro
L
H
H
L
2
D
calc
group in the aromatic ring.
molecules. Therefore, in the calculations of the dipole
moments and molar Kerr constants of compounds
II IX we used molecular conformations determined
on the basis of the X-ray diffraction data and dihedral
angles calculated by the B3LYP/6-31G* method
(Table 3). As a rule, the calculated dihedral angles
Table 3. Experimental (numerator, according to the X-ray diffraction data) and calculated (denominator, B3LYP/6-31G*)
dihedral angles used in the calculation of the dipole moments ( calc, D) and molar Kerr constants (mK 1012) of com-
pounds II XI by the vector and tensor additive schemes, respectively
Angle
II
III
IV
V
VI
VII
VIII
IX
X
XI [18]
C1N7N8O10
161.97(18)
178.12(16)
179.5(2)
168.4 167.0 168.5
171.9
8.1(3)
168.0 168.6
3.4(3)
13.6
3.0(2)
13.6
177.7(2)
168.8 168.6
116.89(2)
56.2 123.4
86.6(3)
82.4
116.89(2)
124.6 124.0
109.9(3)
97.0
149.27(2)
152.4 150.2
30.2(2)
28.8
180.0
0.0
173.4
7.7
166.7
10.5(4)
180.0
0.0
C11N7N8O10
C1N7N8O9
C11N7N8O9
N8N7C1C6
14.2
14.0
8.8
7.3
1.7(2)
12.3
20.4(3)
13.8
14.6
9.2
1.3(4)
14.5
6.9
9.8
174.3(2)
0.0
13.0
14.7
168.8(3)
0.0
168.3 172.6 173.8
60.4 60.2 55.8
92.4 143.2 144.3
169.5
66.7(3)
180.0
92.3
87.7
92.3
87.7
154.9
25.7
168.1
53.5
172.1
140.5(3)
180.0
65
67.0
86.6(3)
121.8
29.0(4)
87.8
87.7
92.2
87.7
C11N7C1C6
N8N7C1C2
86.8
82.5
147.5
129.3
29.7
34.2
43.6(4)
72.3(2) 115.9(2)
120.4 122.9 52.5
114.7
90.8(3)
55.2
147.0(3)
C11N7C1C2
C1C2N12O13
C1C2N12O14
C2C3N15O16
92.4
158.4
23.5
33.9 32.5
91.6
91.0(3)
96.6
148.8
128.9
86.3(2)
153.8
25
52.9
10.2(3)
25.2
25.6
178.7
31.8
137.0
178.2
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68
PREZHDO et al.
Table 3. (Contd.)
Angle
II
III
IV
V
VI
VII
VIII
IX
X
XI [18]
C2C3N15O17
171.7(2)
150.7
39.9
36.0
147.0
1.8
C3C4N15O16
C3C4N15O17
C4C5N15O16
1.0
23
0.4
0.0
179.2
0.8
180.0
179.4
5.3(3)
9.2(4)
1.2
174.61(18)
0.9
168.5(3)
C4C5N15O17
178.4
179.4
C5C6N15O16
C5C6N15O17
44
25.6
25.7
154.9
153.8
Table 4. Selected structural parameters: bond lengths ( ) and bond angles (deg) (experimenta/calculationb) of compounds
I, IV, V, VII, X, and XI
Bond or angle
N7 N8
I
IV
V
VII
X
XI
1.345(3)
1.346(3)
1.360(2)
1.352(2)
1.358(2)
1.348
1.3925
1.435(2)
1.3946
1.431(2)
1.3948
1.427(2)
1.3936
1.422(2)
1.3940
1.417(2)
1.3935
1.497
C1 N7
1.4306
1.445(3)
1.4276
1.498(4)
1.4272
1.457(3)
1.4265
1.445(3)
1.4203
1.459(2)
1.4830
1.466
C11 N7
1.4600
121.8(2)
1.4607
122.0(2)
1.4632
120.2(2)
1.4603
122.3(2)
1.4627
121.8(1)
1.4725
118.8
C1N7C11
C1N7N8
C11N7N8
N7N8O9
N7N8O10
O9N8O10
122.03
118.1(2)
121.88
118.8(2)
110.74
116.4(2)
121.56
117.8(1)
122.09
120.4(1)
119.02
117.8
119.04
118.6(2)
119.03
119.1(2)
117.27
118.0(2)
118.07
119.6(2)
121.11
117.0(1)
118.33
118.8
115.41
118.1(2)
116.01
117.8(3)
115.62
116.9(2)
116.67
117.6(2)
115.00
118.5(1)
115.90
117.5
117.93
117.6(2)
117.32
117.1(3)
116.72
117.3(2)
117.32
117.0(2)
118.30
117.6(1)
117.22
116.8
117.93
124.39(2)
115.68
125.1(2)
117.63
125.7(2)
117.22
125.3(2)
116.34
123.9(1)
115.90
125.7
126.12
126.25
126.00
125.96
125.70
126.00
a
b
Data of [3, 18, 20, 21].
Calculated by the B3LYP/6-31G* method.
were in a satisfactory agreement with the data of
crystallographic data. Some deviations are likely to
result from packing effects, as follows, e.g., from
comparison of the p-dinitrobenzene structures in
crystal [13] and in the gas phase [19]. Figure 1 shows
the molecular structures of compounds IV, VI, and
XI. Selected structural parameters (bond lengths and
bond angles) of nitro-substituted N-methyl-N-nitro-
anilines are given in Table 4.
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SYNTHESIS, PROPERTIES, AND MOLECULAR STRUCTURE
69
(a)
(b)
O17
O13
N12
C11
O17
N15
O14
C11
N15
O10
C6
N7
O9
C5
C4
O16
C2
N8
O10
O16
C3
C4
C2
N7
O14
N8
C1
C3
O9
N12
C5
C6
O13
(c)
C11
N7
O17
O10
C9
N15
N8
O16
C1
C5
O9
C2
C4
C3
O13
O14
Fig. 1. Structure of the molecules of (a) N-methyl-N,2,3-trinitroaniline, (b) N-methyl-N,2,5-trinitroaniline, and (c) N-me-
thyl-N,3,5-trinitroaniline.
The data in Tables 3 and 4 indicate that the nitro-
amino group is almost planar, i.e., atoms of the
C2N NO2 fragment lie in one plane. The N7 N8 bond
in both unsubstituted N-methyl-N-nitroaniline (I) (as
well as in its chloro-substituted derivatives [22]) and
in all nitro derivatives is shortened [1.345(3)
1.360(2) ] as compared to the standard single N N
bond (1.48 ) but is considerably longer that the
nitrogen nitrogen bond in nitrous acid esters and azo
compounds (1.25 ) [23]. This means that one couple
of electrons among six electrons occupying a set of
four-center orbitals is transferred to an antibonding
orbital and that the aromatic sextet and electrons of
the nitroamino group give rise to two sets of multi-
center orbitals which are not conjugated with each
other. The dihedral angle between the planes of the
N NO2 fragment and the aromatic ring (N8N7C1C6
and N8N7C1C2) varies over a wide range: from 50.7
for the least sterically hindered compound IX to 87.8
for compounds VIII and XI; i.e., the N NO2 group in
arylnitroamines possessing two nitro groups in the
ortho positions is arranged orthogonally to the
benzene ring plane. Although molecules III, IV, IX,
and X lack nitro groups in the ortho positions, the
corresponding dihedral angles therein suggest the exi-
stence of steric interaction between the (CH3)NNO2
group and the aromatic ring and the absence of con-
jugation between their -electron systems. This is
consistent with the Carom NO2 bond length which
ranges from 1.417(2) to 1.435(2)
aches the standard ordinary Carom N bond length
equal to 1.45 [24].
and thus appro-
The bond lengths and bond angles characterizing
the nitro groups in the aromatic ring are typical of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 1 2006

70
PREZHDO et al.
aromatic nitro compounds [21]. The Carom NO2
bonds range from 1.466(3) to 1.476(2) , i.e., they are
longer by 0.05 than the Carom N bond between the
aromatic ring and the nitroamino group. The dihedral
angles formed by the Carom NO2 groups are given in
Table 3. The para-nitro groups in molecules IV, VI,
and XI, which suffer no steric effect from the neigh-
boring groups, lie in the benzene ring plane; the same
applies to the meta-nitro groups in molecules III and
X.
nitro group resulted only from the conjugation effect.
Taking into consideration a small magnitude of that
effect in nitrobenzene molecule [30] and the pattern
of variation of the nitro group polarity [31], we
presumed that the difference in the polarizability
ellipsoid axes of the NO2 group originates from dif-
ferent modes of hybridization of the corresponding
carbon atoms, and that this difference remains constant
for different steric orientations of aromatic NO2 group.
Thus, in the calculation of molar Kerr constants of
compounds II XI we used the NO2 polarizability
ellipsoids derived from the data for nitrobenzene:
b1 = 5.04 (along the symmetry axis of the NO2 group),
b2 = 2.60 (in the O N O plane), and b3 = 1.31
(orthogonal to the O N O plane) [27]. The parameters
of the N NO2 group were determined by us recently
[32], 3: b1 = 5.28, b2 = 5.79, b3 = 2.01. The param-
eters of other bonds and groups were taken from [27].
Table 2 lists the dipole moments and molar Kerr
constants determined on the basis of the above con-
siderations and molecular conformations defined by
the dihedral angles given in Table 3.
The structure of compounds possessing Carom NO2
bonds was studied in detail by Holden and Dickinson
[25]. In most cases, deviation of the nitro group from
the aromatic ring plane was attributed to low energy
of conjugation between the nitro group and aro-
matic
system. Depending on the nature, number,
and position of the other substituents, the dipole
moment of the nitro group varies over a wide range,
from 3.16 to 4.03 D [26]).
Taking into account the above structural features
of nitro compounds II XI, we calculated their dipole
moments ( calc) by the vector additive scheme [6]
and molar Kerr constants (mKcalc) by the tensor ad-
ditive scheme [27] (Table 2). The parameters for N-
methyl-N-nitroaniline (I) [7] having no nitro groups
in the aromatic ring were taken as initial parameters
for the calculation of dipole moments and molar Kerr
constants. As in [28, 29], we presumed that the aniso-
tropic polarizability of a nitro group attached to an
aromatic ring changes with variation of the degree of
acoplanarity (i.e., degree of conjugation between the
NO2 group and aromatic -electron system). The po-
larizability parameters of the nitro group in a com-
pletely conjugated system were derived from the data
for nitrobenzene. In the calculation of molar Kerr
constants for conformers with orthogonal orientation
of the NO2 group and aromatic ring planes, the para-
meters for nitromethane were used [27]. Therefore,
exaltations and dispersions of the polarizability ellip-
soid axes bi in going from aliphatic to aromatic
Analysis of the data in Table 2 shows that the
contribution of the dipole moment of the C-nitro
group to the total dipole moment of sterically
hindered molecules II, V IX, and XI as a rule de-
creases, presumably due to reduction of the degree of
conjugation between the nitro group and aromatic
ring. Depending on that factor, the dipole moment of
the nitro group may change from to 3.97 to 3.10 D
[26], which affects in turn the total dipole moment
of mono-, di-, and trisubstituted benzene derivatives.
The nitro group in molecules III, IV, and X lies in the
benzene ring plane (Table 3); therefore, the corres-
ponding
are small, reflecting only a weak interac-
tion between the C-nitro and nitroamino groups.
This interaction is mainly inductive since the nitro-
amino group is forced out from conjugation with the
benzene ring. In molecules II, V VIII, and XI, one
or two nitro groups are partially turned out from the
aromatic ring plane (the dihedral angle is 23.5 25.7 ).
In this case, conjugation between the nitro group and
aromatic ring is disrupted, which affects the total
1.0
1
0.8
0.6
dipole moment (Table 2): The
value is larger than
0.4
2
that found for molecules III, IV, and X. The effect of
the para-nitro group in molecules VI and XI may
interpreted in terms of competing conjugation which
makes the interaction between the 2-NO2 and 6-NO2
groups and the aromatic ring weaker, thus facilitating
their rotation due to steric repulsion [27]. The
0.2
0
3 4 2 3,5 2,6 2,5 2,4 2,3 3,4 2,4,6
PNNO
2
Fig. 2. Plots of (1) the interaction moment ( ) between
the C NO and nitroamino groups through the
maximal
value is observed for compound IX; both
2
aromatic ring and (2) the interaction moment per C NO
nitro groups in molecule IX are turned through an
2
group (
) vs. the number and position of C NO
angle of 40 with respect to the benzene ring plane.
1
2
groups (PN
).
Figure 2 illustrates the dependence of
on the
NO2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 1 2006

SYNTHESIS, PROPERTIES, AND MOLECULAR STRUCTURE
71
Table 5. Calculated dipole moments ( , D) and molar Kerr constants (mK 1012) of compounds II XI
Comp.
no.
Calculation
method
mK
3
3
3
3
3
3
x, D
y, D
z, D
, D bxx,
byy,
bzz,
bxy,
bxz,
byz,
1012
II
HF/6-31G*
5.299 5.052 2.980 7.905 18.739 15.113 8.862 0.204 1.642 0.578
1325
1745
1498
1007
595.2
305.7
1335
10.16
516.3
598.0
1077
769.7
2410
1838
367.0
1619
928.9
175.2
1359
B3LYP/6-31G* 4.419 4.552 2.636 7.134 20.763 16.594 9.547 0.663 1.516 0.676
HF/6-31G* 0.488 2.386 4.146 4.771 18.969 15.751 8.432 1.336 0.707 0.024
B3LYP/6-31G* 0.506 1.045 2.941 3.162 22.752 17.705 8.046 1.023 0.247 0.247
HF/6-31G* 1.978 3.081 2.698 4.548 20.590 13.996 9.041 0.759 0.596 2.014
B3LYP/6-31G* 2.299 3.169 1.735 4.282 26.027 16.059 8.091 0.516 0.326 1.426
HF/6-31G* 0.803 6.310 4.527 7.807 19.876 17.213 11.412 1.173 1.507 0.495
B3LYP/6-31G* 0.276 7.468 2.919 8.023 22.530 18.902 12.068 1.049 2.104 0.283
HF/6-31G* 0.384 5.156 3.323 6.146 22.567 17.232 9.449 0.201 1.366 0.680
B3LYP/6-31G* 0.236 4.805 2.836 5.584 26.654 18.646 10.094 0.016 1.203 0.799
HF/6-31G* 2.336 0.500 3.449 4.195 21.148 18.356 9.596 1.383 0.784 1.566
B3LYP/6-31G* 2.070 0.184 2.991 3.642 24.989 19.690 10.224 0.981 0.594 1.514
HF/6-31G* 6.626 2.552 0.000 7.100 20.740 10.076 17.632 0.570 0.000 0.000
B3LYP/6-31G* 5.858 2.430 0.000 6.342 22.892 10.782 20.190 0.697 0.000 0.000
HF/6-31G* 4.108 0.576 3.889 5.686 21.860 17.345 10.293 0.931 1.006 1.311
B3LYP/6-31G* 4.039 0.339 2.627 4.830 27.445 19.587 9.828 0.915 0.481 1.171
HF/6-31G* 1.999 1.188 3.920 4.558 21.767 18.119 9.371 0.369 1.339 0.201
B3LYP/6-31G* 1.994 2.571 2.518 4.114 25.548 21.669 8.804 0.427 0.748 0.548
HF/6-31G* 3.632 1.349 0.000 3.874 10.776 24.170 19.740 0.129 0.000 0.000
B3LYP/6-31G* 3.355 1.150 0.000 3.547 11.579 28.894 22.117 0.081 0.000 0.000
III
IV
V
VI
VII
VIII
IX
X
XI
1409
number and position of nitro groups in molecules of
the compounds under study. The general tendency is
that accumulation of nitro groups increases
not coincide but form a considerable angle [33]. Small
exaltations of the molar Kerr constants ( mK) may be
rationalized in terms of small
values and change
(curve 1). On the other hand,
values (i.e.,
per
of the anisotropic polarizability of the Carom NO2
group due to variation of the degree of its conjugation
with the aromatic -electron system. The C NO2
groups in molecules III, IV, and IX are coplanar to
the aromatic ring (Table 3), and the corresponding
mK values are minimal (Table 2). The maximal mK
values were obtained for compound IX, in the mole-
cule of which both C-nitro groups deviate from co-
planarity by an angle of 40 , and for compound V
where the C-nitro group is completely forced out from
conjugation with the aromatic ring (the dihedral angle
C1C2N12O13 is 91 ); therefore, the polarizability
ellipsoid parameters of the nitro group in V are
1
nitro group) for different compounds oscillate about
0.3 D, reflecting a weak interaction between C-nitro
and nitroamino group.
Molar Kerr constants are more sensitive to intra-
molecular interactions than dipole moments, for the
former are determined not only by variations in the
dipole moments but also by transformation of the
bond polarizability ellipsoids, which accompanies
such interactions [27, 33]. One of the most important
parameters characterizing interactions between atoms
which are not linked through a covalent bond is devia-
tion of the polarizability parameter of a molecule from
that calculated by the additivity scheme, i.e., without
taking into account these interactions. In the general
case, the existence of such interactions follows from
exaltation of the molar Kerr constant: mK = mKexp
mKcalc, where mKexp is the experimental molar Kerr
constant, and mKcalc is that calculated by the tensor-
additivity scheme from known molecular conforma-
tion [34]. The molar Kerr constants of all the ex-
amined nitro-substituted N-methyl-N-nitroanilines are
negative, i.e., the directions of the largest polarizabi-
lity axis and the dipole moment of their molecules do
3
similar to those of the Csp NO2 group in nitro-
methane (b1 = 3.4, b2 = 2.8, b3 = 2.3 3) [27], and the
polarizability exaltation attains is maximal value:
b1 = 1.64, b2 = 0.2, b3 = 0.99 3).
Table 5 contains the dipole moments and molar
Kerr constants of compounds II XI, calculated by the
HF/6-31G* and B3LYP/6-31G* quantum-chemical
methods with full geometry optimization; the princi-
pal geometric are given in Tables 3 and 4. The cal-
culated dipole moments (Table 2) agree satisfactorily
with the experimental data. For compounds II, IV, VI,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 1 2006

72
PREZHDO et al.
VIII, and X, the experimental data matched best those
calculated by the B3LYP/6-31G* method, and for the
other compounds, by HF/6-31G*. While comparing
experimental and calculated dipole moments, it should
be kept in mind that the dipole moments measured in
nonpolar solvents are always smaller by 0.3 0.5 D
than the data obtained for the gas phase (so-called
solvent effect) [35]. Just the same pattern was ob-
served with the experimental and calculated dipole
moments of compounds II XI. Compound V was
characterized by the largest difference (>1 D) between
the experimental and calculated dipole moment, and
differences were also found between the geometric
parameters (specifically dihedral angles) determined
experimentally and calculated by quantum-chemical
methods. Differences in the angles of rotation of the
2-NO2 and 3-NO2 groups with respect to the benzene
ring plane ranged from 21.0 to 37.9 . Taking into
account the fan-like structure of such sterically hin-
dered molecules [21], the error in determination of the
moment of conjugation between the nitro group and
benzene ring may be fairly large.
aromatic ring exerts some effect on the N NO2 group,
which leads to variation of the charge on N7, depend-
ing on the number and position of C NO2 groups in
the molecule: The charge on N7 is minimal in absolute
value if one or two C NO2 groups are present in the
ortho position with respect to the N NO2 group.
Decrease of the charge on N7 is accompanied by in-
crease of the charge on N8, the latter attaining its
maximal value for the 2,4,6-trinitro derivative. The
charge on C1 is also fairly sensitive to the nitro
substitution pattern in the aromatic ring: It changes
from 0.2685 for compound II to 0.3288 for IV
(B3LYP/6-31G* calculations). HF/6-31G* calcula-
tions give a different series of charge variation on C1:
The minimal value is obtained for compound III
(0.2532), and the maximal, for XI (0.3916). The
charges on C11, O9, and O10 turned out to be less
sensitive to the effect of C-nitro groups; as a rule,
variations only in the second decimal point were ob-
served, regardless of the number and position of nitro
groups in the aromatic ring. These data support our
previous conclusion [20] that n electrons on the amino
nitrogen atom are involved mainly in conjugation with
electrons of the N-nitro group rather than with the
aromatic ring; as a result, the nitroamino group
becomes less sensitive to various interactions.
An analogous pattern was observed for the calcu-
lated (Table 5) and experimental molar Kerr constants
(Table 2) of compound V. In this case, the difference
is even greater since the dipole moment contribution
to the molar Kerr constant is supplemented by the
anisotropic polarizability contribution which is es-
pecially sensitive to the molecular geometry. Com-
parison of the angles of rotation of the C NO2 and
N NO2 groups in the 2,5- and 3,5-dinitro derivatives,
determined from the crystallographic data and cal-
culated by quantum-chemical methods (Table 3),
shows that the difference for sterically unhindered
positions 3 and 5 attains 11 . The nitro group not only
is strongly polar, but also is characterized by a fairly
high anisotropic polarizability ( = 0.6 3.08 3) [27];
therefore, even a small angle (5 10 ) of rotation of
that group strongly affects the molar Kerr constant
[15]. Moreover, the experimental molar Kerr constants
depend to a considerable extent on the solvent nature.
As a rule, molar Kerr constants measured in a solvent
are lower than in the gas phase even if donor acceptor
interaction between the solvent and the solute is
lacking (i.e., there are only universal interactions) [36].
The above reasons make it impossible to compare the
calculated (Table 5) and experimental molar Kerr
constants (Table 2).
Thus, the nitroamino group can be regarded as an
independent functional group possessing a four-center
-orbital system. It acts as a weak electron donor with
respect to Carom NO2 groups according to the inductive
mechanism. No conjugation exists between
elec-
trons of the nitroamino group and the aromatic ring.
The presence of nitro groups in the aromatic ring of
N-methyl-N-nitroaniline derivatives almost does not
affect the geometric parameters of the nitroamino
group. The moment of interaction between the C- and
N-nitro groups through the aromatic ring depends on
the number and position of the former. Nitro groups
in the aromatic ring weakly affect charge distribution
over the nitroamino group. Taking into account the
weak effect of aromatic nitro groups on the nitroamino
group, we presume that the ability of nitro-substituted
N-methyl-N-nitroanilines to undergo acid-catalyzed
rearrangement weakly depends on the interaction of
the nitroamino group with other substituents in the
aromatic ring.
EXPERIMENTAL
The nitroamino group is strongly polar. According
to the results of quantum-chemical calculations, a
large positive charge resides on N7 while all neigh-
boring atoms possess a negative charge (Table 6).
Analysis of the charge distribution pattern over the
N7, N8, C1, C11, O9, and O10 atoms shows that the
Dielcometric measurements were performed at
25 C using a WTW DMO-1 setup (Germany). The
dielectric constants ( ) and densities ) of dilute solu-
tions (up to 5 10 M) of compounds II XI in
benzene were measured. The P2 values (molar
3
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 1 2006

SYNTHESIS, PROPERTIES, AND MOLECULAR STRUCTURE
73
Table 6. Charges on atoms in the molecules of nitro-substituted N-methyl-N-nitroaniline, calculated by the HF/6-31G*
(numerator) and B3LYP/6-31G* methods (denominator)
Atom
C1
II
III
IV
V
VI
VII
VIII
IX
X
XI
0.2655 0.2971
0.2991 0.2532
0.3161 0.1842
0.2330 0.1600
0.1590 0.2685
0.1768 0.1490
0.1295 0.1423
0.2068 0.1595
0.1196 0.1550
0.1793 0.2272
0.1533 0.0918
0.2075 0.1348
0.3712 0.3859
0.5415 0.5483
0.6618 0.6435
0.8638 0.8492
0.4259 0.4175
0.5128 0.5053
0.4096 0.4076
0.4913 0.4990
0.3092 0.3163
0.2772 0.2837
0.3649 0.3840
0.5016 0.5221
0.3943 0.3926
0.4451 0.4636
0.3729 0.3775
0.4744 0.4671
0.3288
0.2966
0.1699
0.2055
0.1599
0.1752
0.2858
0.1599
0.1655
0.1785
0.1259
0.1768
0.3884
0.5543
0.6440
0.8494
0.4133
0.5028
0.4061
0.4995
0.3163
0.2829
0.3795
0.5215
0.3905
0.4663
0.3933
0.4626
0.2671
0.2925
0.3100
0.2519
0.2636
0.2190
0.1336
0.1621
0.1394
0.2114
0.1256
0.1337
0.3839
0.5700
0.6560
0.8588
0.4192
0.4970
0.4046
0.4852
0.3081
0.2759
0.3564
0.5183
0.3636
0.4210
0.3399
0.4390
0.3664
0.5058
0.3650
0.4468
0.3624
0.4465
0.2924
0.3251
0.3100
0.2269
0.1873
0.1456
0.2791
0.1477
0.1369
0.1437
0.1677
0.2232
0.3759
0.5435
0.6639
0.8668
0.4187
0.4787
0.3981
0.5094
0.3128
0.2829
0.3696
0.5079
0.3868
0.4688
0.3542
0.4330
0.3875
0.5274
0.3762
0.4526
0.3821
0.4592
0.2774
0.2973
0.3300
0.2621
0.1676
0.1904
0.1499
0.1704
0.2930
0.1740
0.1912
0.1820
0.3769
0.5462
0.6638
0.8657
0.3997
0.4903
0.4217
0.5112
0.3127
0.2804
0.3659
0.5005
0.3810
0.4310
0.3592
0.4606
0.3863
0.5238
0.3772
0.4533
0.3790
0.4544
0.2754
0.3654
0.2840
0.1989
0.1346
0.1440
0.1420
0.2213
0.1346
0.1440
0.2840
0.1989
0.3699
0.5633
0.7016
0.9111
0.4137
0.4957
0.4377
0.5176
0.3190
0.2811
0.3590
0.4905
0.3736
0.4316
0.3629
0.4535
0.3541
0.4905
0.3629
0.4535
0.3736
0.4316
0.3294
0.2870
0.1894
0.1764
0.2698
0.2308
0.2798
0.2377
0.1632
0.1907
0.1088
0.1456
0.3967
0.5597
0.6479
0.8504
0.3959
0.4874
0.4090
0.5016
0.3224
0.2913
0.3969
0.5010
0.3777
0.4424
0.3758
0.4309
0.3655
0.5008
0.3629
0.4359
0.3862
0.4347
0.3061
0.2386
0.1705
0.1247
0.2659
0.1347
0.1723
0.1234
0.2549
0.1339
0.1214
0.1050
0.3944
0.5471
0.6492
0.8534
0.3962
0.4890
0.4082
0.5023
0.3208
0.2868
0.3901
0.5275
0.3736
0.4609
0.3862
0.4513
0.3911
0.5262
0.3777
0.4560
0.3758
0.4532
0.2950
0.3916
0.2790
0.1893
0.1619
0.1090
0.2742
0.1393
0.1619
0.1090
0.2700
0.1893
0.3729
0.5636
0.7040
0.9138
0.4049
0.4845
0.4333
0.5167
0.3224
0.2847
0.3647
0.4956
0.3567
0.4265
0.3611
0.4426
0.3930
0.5318
.3687
C2
C3
C4
C5
C6
N7
N8
O9
O10
C11
N12
O13
O14
N15
O16
O17
N18
O19
O20
0.4469
0.3687
0.4469
0.3647
0.4966
0.3567
0.4426
0.3611
0.4265
polarization of a solute, extrapolated to infinite dilu-
tion) were calculated according to Hedestrand [37].
The values of NH = d /dN2 (where N2 is the mole
fraction of a solute), = d /dN2, P2 , PD = 1.1RD (RD
mined using a setup and procedure described in [33].
The refractive indices (nD) were measured on an IRF-
23 refractometer. To calculate molar Kerr constants
(mK), the measured data were treated by the procedure
described in [38]. Concentration dependences of the
measured parameters of solutions were expressed in
is molar refraction), and
are given in Table 2.
exp
The dipole moments were calculated ( calc) according
to the vector additive scheme using the data of [6, 28,
29]. The Kerr constants of solutions (B) were deter-
the following forms:
=
1(1 +
2),
=
1(1 +
L
2), n = n1(1 +
2), B = B1(1 + 2), where
L
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 1 2006

74
PREZHDO et al.
is the weight concentration of a solution, and
,
,
REFERENCES
1
n1, and B1 are the corresponding solvent param1eters.
1. White, W.N., Hathway, C., and Huston, D., J. Org.
Chem., 1970, vol. 35, no. 3, p. 737.
The data were extrapolated to infinite dilution by
graphical methods. The values of
, L, , , and mK
are given in Table 2. Tensor additLive calculations of
the molar Kerr constants (mKcalc) were performed
using the data of [27, 32]. Ab initio quantum-chemical
calculations were performed with the aid of the
GAUSSIAN-98 software.
2. Ridd, J.H. and Scriven, E.F.V., J. Chem. Soc., Chem.
Commun., 1972, no. 2, p. 641.
3. Anulewicz, R., Krygowski, T.M., Gawiniecki, R., and
Rasala, D., J. Phys. Org. Chem., 1993, vol. 6, p. 257.
4. Ejsmont, K., Kyziol, J.B., Daszkiewicz, Z., and
Bujak, M., Acta Crystallogr., Sect. C, 1998, vol. 54,
no. 5, p. 672.
The IR spectra were recorded in KBr on a Philips
PU-9804FTIR spectrometer. The electronic absorption
spectra were measured from solutions in methanol on
a Beckman DU-640B spectrophotometer. X-Ray dif-
fraction studies were performed at room temperature
on a KUMA KM-4 diffractometer ( MoK radiation);
the experimental conditions and crystallographic data
were reported in detail previously [21]. The dihedral
angles are given in Table 4.
5. Prezhdo, V.V., Daszkiewicz, Z., Kyziol, J.B., Byko-
va, A.S., and Prezhdo, O.V., Zh. Org. Khim., 2000,
vol. 36, no. 3, p. 429.
6. Minkin, V.I., Osipov, O.A., and Zhdanov, Yu.A.,
Dipol’nye momenty v organicheskoi khimii (Dipole
Moments in Organic Chemistry), Leningrad: Khimiya,
1968.
7. Daszkiewicz, Z., Nowakowska, E., Prezhdo, V.V.,
and Kyziol, J.B., Polish J. Chem., 1995, vol. 69,
p. 1436.
N-Nitro amines II X were synthesized from the
corresponding nitro-substituted N-methylanilines by
nitration with a mixture of nitric acid and acetic
anhydride. This procedure was successfully used pre-
viously to obtain N-nitroazoles [39]. The progress of
reactions and the purity of products were monitored
by gas liquid chromatography. Nitro amines I and II
were subjected to rearrangement in concentrated sul-
furic acid, and the products were separated by thin-
layer chromatography and subjected to nitration as
shown in Scheme 1. N-Methyl-N,3,5-trinitroaniline
(X) was synthesized by methylation of 3,5-dinitro-
aniline, followed by nitration in acetic anhydride. N-
Methyl-N,2,4,6-tetranitroaniline (XI) was synthesized
by nitration of N-methyl-2,4-dinitroaniline with
8. Hughes, E.D. and Jones, G.T., J. Chem. Soc., 1950,
no. 10, p. 2678.
9. Glazer, J., Hughes, E.D., Ingold, C.K., James, A.T.,
Jones, G.T., and Roberts, E., J. Chem. Soc., 1950,
no. 10, p. 2657.
10. Avram, M. and Mateescu, Gh.D., Infrared Spec-
troscopy. Application in Organic Chemistry, New
York: Wiley, 1972, pp. 307 311.
11. Colthup, N.D., Daly, L.H., and Wiberley, S.E., Intro-
duction to Infrared and Raman Spectroscopy, New
York: Academic, 1964, pp. 286 287.
12. Gowenlook, B.G., Ptab, J., and Young, V.M., J. Chem.
Soc., Perkin Trans. 2, 1997, no. 5, p. 915.
fuming nitric acid (d425 = 1.52 g cm ) in 80% sulfuric
3
13. Kitaigorodskii, A.I., Zorkii, P.M., and Bel’skii, V.K.,
Struktura organicheskogo veshchestva. Dannye
rentgenostrukturnykh issledovanii (Structure of Or-
ganic Compounds. X-Ray Diffraction Data), Moscow:
Nauka, 1980.
acid. As an example, the procedure for the preparation
of N-methyl-N,3,5-trinitroaniline (X) is given below.
N-Methyl-3,5-dinitroaniline (mp 158 160 C), 1.58 g,
was dissolved in 1 ml of 100% nitric acid, a solution
of 1.00 g of hydroxamic acid in 20 ml of acetic an-
hydride was added, and the mixture was kept for 2 h
at room temperature and was distilled under reduced
pressure. The nonvolatile residue was recrystallized
from benzene hexane to obtain 1.73 g of compound
X with mp 94 98 C. The product was recrystallized
once more from methylene chloride n-hexane. Yield
1.68 g (87%), slightly yellowish sticks with mp 111
112 C. Some crystals were suitable for X-ray analysis.
Mass spectrum, m/z (Irel, %): 240 (1) [M]+, 196 (100),
150 (54), 104 (95), 91 (1). 1H NMR spectrum
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