Structure and properties of some nitro derivatives of N-methyl-N-phenylnitramine

Article abstract of DOI:10.1016/S0022-2860(00)00445-2

Ten mono-, di- and tri-nitro derivatives of N-methyl-N-phenylnitramine were prepared and investigated using spectral and electrooptical methods. Three of them, viz. N-(2, 5-dinitrophenyl)-N-methylnitramine (monoclinic, P2₁/c, a = 8.248(2), b = 11.655(2), c = 10.404(2) ?, β = 102.57(2)°), N-(2,3-dinitrophenyl)-N-methylnitramine (monoclinic, P2₁/c, a = 9.224(2), b = 7.222(2), c = 15.458(4) ?, β = 101.08(2)°)) and N-(3,5-dinitrophenyl)-N-methylnitramine (monoclinic, P2₁/n, a = 9.814(2), b = 12.000(2), c = 8.865(2) ?, β = 114.94(2)°) were examined by the X-ray diffraction method. The nitramino group is nearly planar with the short N(7)-N(8) bond and strongly electron deficient N(8) atom. The nitramino group is twisted vs. the aromatic ring, there is no conjugation between the nitro and nitramino groups across the ring. The nitramino group is an electron withdrawing substituent due to the inductive effect. The number and positions of the At-nitro groups have no influence on the N-nitro group. Its migration ability cannot be explained in terms of the interaction between the migration origin and the ring substituents. (C) 2000 Elsevier Science B.V.

Full text of DOI:10.1016/S0022-2860(00)00445-2

Journal of Molecular Structure 553 (2000) 9–18
www.elsevier.nl/locate/molstruc
Structure and properties of some nitro derivatives of
N-methyl-N-phenylnitramine
Z. Daszkiewicza, J.B. Kyzioła, W.W. Prez˙dob, J. Zaleskia,
*
aInstitute of Chemistry, University of Opole, 45-052 Opole, ul.Oleska 48, Poland
b
´
Institute of Chemistry, Pedagogical University, 25-020 Kielce, ul.Che˛cinska 5, Poland
Received 13 September 1999; received in revised form 17 December 1999; accepted 19 January 2000
Abstract
Ten mono-, di- and tri-nitro derivatives of N-methyl-N-phenylnitramine were prepared and investigated using spectral and
electrooptical methods. Three of them, viz. N-(2, 5-dinitrophenyl)-N-methylnitramine (monoclinic, P21/c, a ˆ 8:248ꢀ2†; b ˆ
ꢀ
11:655ꢀ2†; c ˆ 10:404ꢀ2† A; b ˆ 102:57ꢀ2†Њ†; N-(2,3-dinitrophenyl)-N-methylnitramine (monoclinic, P21/c, a ˆ 9:224ꢀ2†; b ˆ
ꢀ
7:222ꢀ2†; c ˆ 15:458ꢀ4† A; b ˆ 101:08ꢀ2†Њ†) and N-(3,5-dinitrophenyl)-N-methylnitramine (monoclinic, P21/n, a ˆ 9:814ꢀ2†;
ꢀ
b ˆ 12:000ꢀ2†; c ˆ 8:865ꢀ2† A; b ˆ 114:94ꢀ2†Њ† were examined by the X-ray diffraction method. The nitramino group is nearly
planar with the short N(7)–N(8) bond and strongly electron deficient N(8) atom. The nitramino group is twisted vs. the aromatic
ring, there is no conjugation between the nitro and nitramino groups across the ring. The nitramino group is an electron
withdrawing substituent due to the inductive effect. The number and positions of the Ar-nitro groups have no influence on
the N-nitro group. Its migration ability cannot be explained in terms of the interaction between the migration origin and the ring
substituents. ᭧ 2000 Elsevier Science B.V. All rights reserved.
Keywords: Nitramines; Dipole moments; X-ray diffraction; FTIR spectra
1. Introduction
arylnitramines. On the other hand, rentgenostuctural
analyses of N-methyl-N-phenylnitramine and its ring
substituted derivatives indicated that nitramine p-
electron system is not conjugated with the aromatic
sextet [3,4]. That means that the formally unshared
electron pair on the amido nitrogen is delocalised
towards the N-nitro group and does not interact with
the p-electrons of the ring. Consequently, we have
observed that the dipole moments of the series of
nitramines obey the additivity rule, i.e. they are vector
sums of the contributions coming from the substituted
ring and the nitramino group [5]. Therefore, it may be
reasonably assumed that introduction of 1-3 nitro
groups, strong electron-withdrawing substituents, to
the aromatic ring, would change the charge distribu-
tion within the molecule. The shift of the nitrogen
The rearrangement of aromatic nitramines is an
acid catalysed reaction, however, requirements of
acidities are strongly dependent on the substrate. N-
Methyl-N-phenyl-nitramine can be rearranged in
dilute (0.1 M) sulphuric acid [1], while the rearrange-
ment of N-(2,3-dinitrophenyl)-nitramine only occurs
in a concentrated (78%) acid at room temperature [2].
Such a difference suggests that the nitramino group is
strongly influenced by the ring substituents. This
interaction, which determines the migration ability
of the N-nitro group, should be reflected with some
spectral and electrooptical properties of the secondary
* Corresponding author.
0022-2860/00/$ - see front matter ᭧ 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(00)00445-2

10
Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
Table 1
Crystal data and structure refinement for N-methyl-N-(2,3-dinitrophenyl)-nitramine (4) N-methyl-N-(2,5-dinitrophenyl)-nitramine (6) and N-
methyl-N-(3,5-dinitrophenyl)-nitramine (9)
Identification code
6
4
9
Empirical formula
Formula weight
Temperature
CH3NNO2C6H3(NO2)2
242.16
293(2) K
˚
Wavelength
0.71073 A
Crystal system,
Space group
Monoclinic
P21/c
P21/c
P21/n
˚
Unit cell dimensions a (A)
8.248(2)
11.655(2)
10.404(2)
102.57(2)
976.2(3)
1.648
9.224(2)
7.222(2)
15.458(4)
101.08(2)
1010.6(3)
1.592
9.814(2)
12.000(2)
8.865(2)
114.94(2)
946.7(3)
1.699
˚
b (A)
˚
c (A)
b (Њ)
3
˚
Volume (A )
Calculated density (Mg/m3)
Z
4
4
4
Absorption coefficient (mmϪ1
)
0.14(1)
F(000)
496
Theta range for data collection (Њ)
Index ranges
2.5–30.1
2.5–25.1
Ϫ 10 Ϲ h Ϲ 9
0 Ϲ k Ϲ 7
0 Ϲ l Ϲ 18
1670/1609
2.5–30.0
Ϫ 12 Ϲ h Ϲ 13
0 Ϲ k Ϲ 16
Ϫ 11 Ϲ h Ϲ 11
0 Ϲ k Ϲ 16
0 Ϲ l Ϲ 14
2955/2836
Ϫ 11 Ͻ ˆ l Ͻ ˆ 0
Reflections collected/independent
Refinement method
2859/2701
Full-matrix least-squares on F2
Number of parameters
Goodness-of-fit on F2
Final R indices (I Ͼ 2s(I)) R1
wR2
R indices (all data) R1
wR2
178
1.106
178
1.060
178
1.023
0.0375
0.0997
0.1203
0.1299
0.181/Ϫ0.144
0.0370
0.1022
0.0492
0.1110
0.197/Ϫ0.186
0.0354
0.1126
0.0714
0.1341
0.251/Ϫ0.232
Ϫ3
˚
Largest diff. peak and hole (e.A
)
lone pair towards the ring should be reflected in values
of dipole moments of the compounds, their spectral
properties and the overall geometry of the molecules.
We have prepared and examined ten one, two and
trinitro derivatives of N-methyl-N-phenylnitramine.
We present the results that have been obtained in
this article.
tion by the Halvestrand method [6]. The infrared
spectra were recorded on the Philips PU9804 FTIR
spectrometer in KBr pellets. The electronic spectra
were registered in methanolic solutions ꢀc ˆ
0:4 × 10Ϫ4 to 1:4 × 10Ϫ4 M† at 25ЊC using Beckman
DU 640B Spectrometer. The calculations of the dipole
moments were performed employing WinMopac 2.0
molecular orbital program [7].
The X-ray data collection were carried out on a
single crystal KM4 KUMA diffractometer using
Mo Ka radiation at room tempreature. Lattice para-
meters were refined from setting angles of 20–34
reflections in the 12Њ Ͻ 2u Ͻ 28Њ range. During data
collections, the v –u scan technique was used. Two
control reflections measured after the interval of 50
reflections indicated that the intensity variations were
negligible. The structures were solved by direct
2. Experimental
The dipole moments were determined at 25ЊC with
the use of Dipolmeter DM 01 (WTW, Germany). The
measurements of dielectric constants and densities
were performed in diluted solutions (to 0.005 mole
fraction of the solute) in benzene. The polarisation
of the molecules was extrapolated to the infinite dilu-

Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
11
Table 2
Table 2 (continued)
Atomic coordinates [ × 104] and equivalent isotropic displacement
2
3
˚
parameters [A × 10 ] for N-methyl-N-(2,3-dinitrophenyl)-nitra-
mine (4) N-methyl-N-(2,5-dinitrophenyl)-nitramine (6) and N-
methyl-N-(3,5-dinitrophenyl)-nitramine (9). Ueq is defined as one
third of the trace of the orthogonalized Uij tensor
x
y
z
Ueq
50(1)
54(1)
40(1)
60(1)
56(1)
O(13)
O(14)
N(15)
O(16)
O(17)
853(1)
811(1)
Ϫ3063(2)
Ϫ2151(2)
Ϫ4313(2)
7400(1)
6073(1)
8814(2)
10 427(2)
8753(2)
8528(2)
8534(2)
10 084(1)
10 667(1)
10 393(1)
x
y
z
Ueq
6
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
N(7)
N(8)
O(9)
O(10)
C(11)
N(12)
O(13)
O(14)
N(15)
O(16)
O(17)
4
3238(2)
1875(2)
288(2)
4264(2)
4857(2)
4446(2)
3408(2)
2828(2)
3234(2)
4643(1)
5629(1)
6109(1)
5959(1)
4069(3)
5961(2)
6641(2)
6153(1)
1727(2)
1333(2)
1273(1)
1692(2)
1937(2)
1524(2)
880(2)
39(1)
42(1)
51(1)
52(1)
45(1)
43(1)
46(1)
50(1)
63(1)
72(1)
75(1)
57(1)
98(1)
72(1)
61(1)
101(1)
80(1)
methods and refined by a full-matrix least squares
method using the shelx97 program [8]. The Lorentz
and polarisation corrections were applied. All
hydrogen atoms were located from the difference
Fourier synthesis. The non-hydrogen atoms were
refined anisotropically. The temperature parameters
for the hydrogen atoms were freely refined. The
details of the data collection and processing are listed
in Table 1, whereas the atomic coordinates and the
equivalent atomic displacement parameters are
presented in Table 2. A list of the calculated and
observed structure factors may be obtained from
authors on request.
29(2)
1382(2)
2978(2)
4909(2)
5346(2)
4292(2)
6775(2)
6090(4)
2079(2)
941(3)
3345(2)
1135(2)
Ϫ258(2)
2337(2)
651(2)
1036(2)
2109(2)
1589(2)
749(2)
1984(2)
3137(3)
2627(2)
2333(2)
3435(2)
Ϫ63(2)
Ϫ339(2)
Ϫ339(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
N(7)
N(8)
O(10)
O(9)
C(11)
N(12)
O(13)
O(14)
N(15)
O(16)
O(17)
9
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
N(7)
N(8)
O(9)
O(10)
C(11)
N(12)
7977(2)
7368(2)
6997(2)
7293(3)
7963(3)
8282(3)
8224(2)
9654(2)
9878(2)
10602(2)
7084(3)
7174(2)
6033(3)
8216(2)
6292(2)
5840(2)
6230(3)
53(3)
6868(1)
6932(1)
7719(1)
8443(2)
8382(2)
7598(2)
6029(1)
5959(1)
5343(1)
6505(1)
5439(2)
6142(1)
5630(1)
6050(2)
7793(2)
8461(2)
7190(2)
42(1)
40(1)
49(1)
68(1)
76(1)
1(1)
49(1)
51(1)
70(1)
66(1)
64(1)
55(1)
100(1)
94(1)
68(1)
107(1)
98(1)
The nitramines were prepared from the corre-
sponding nitro derivatives of N-methyl-aniline using
the well-known methods. The procedure of N-nitra-
tion is exemplified below.
Ϫ1671(3)
Ϫ2217(3)
Ϫ1073(5)
606(5)
1188(4)
655(3)
935(2)
1870(2)
171(2)
1686(4)
Ϫ2848(3)
Ϫ2763(3)
Ϫ3776(3)
Ϫ4013(4)
Ϫ4327(4)
Ϫ5118(3)
N-(3,5-Dinitrophenyl)-N-methylnitramine.
3,5-
Dinitro-N-methylaniline (1.58 g, 8.0 mmol, mp 158–
160ЊC) was dissolved in the solution of absolute nitric
acid (1.0 ml, 22 mmol) and hydroxamic acid (1.00 g)
in acetic anhydride (20 ml). The mixture was left at
room temperature for 2 h and evaporated in vacuum.
The residue was dissolved in methanol (20 ml) to
get rid of the residual anhydride, and evaporated.
The non-volatile residue was crystallised from the
benzene–hexane mixture yielding the crude
product (1.73 g, mp 94–98ЊC). It was recrystallised
from the methylene chloride-n-hexane mixture. N-
(3,5-Dinitrophenyl)-N-methylnitramine (1.68 g, 87%)
was obtained as light yellow rods melting at 111–
112ЊC. The crystals were suitable for the X-ray
analysis. MS, m/z (int.): 240 (Mϩ, 1), 196 (100),
150 (54), 104 (95), 91 (1), 75 (38), 63 (95). 1H-
NMR (DMSO-d6): 8.89, s, 3H (aromatic protons,
overlapped); 3.77, s, 3H (N-methyl group). 13C
NMR (DMSO-d6): 148.3 (C-3, C-5); 141.7 (C-1);
127.9 (C-2, C-6); 118.6 (C-4).
Ϫ3214(2)
Ϫ1929(2)
Ϫ1041(2)
Ϫ1357(2)
Ϫ2643(2)
Ϫ3578(2)
Ϫ4238(1)
Ϫ3727(2)
Ϫ2373(1)
Ϫ4659(2)
Ϫ5848(2)
312(1)
7208(1)
6741(1)
7414(1)
8511(1)
8928(1)
8314(1)
6564(1)
5833(1)
5747(1)
5291(1)
6794(2)
6925(1)
10 223(2)
10 182(2)
9706(2)
9243(2)
9285(2)
32(1)
33(1)
32(1)
34(1)
33(1)
35(1)
38(1)
40(1)
55(1)
55(1)
47(1)
36(1)
9772(2)
10 603(2)
11 894(2)
12 710(2)
12 156(2)
9847(3)
9650(2)

12
Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
Table 3
Characteristics of the nitro derivatives of N-methyl-N-phenylnitramine
No
Substituents
Melting point (ЊC)
IR, n (NO2), cmϪ1
UV (MeOH) lmax, nm (e)
Symmetric
Asymmetric
1
2
3
4
5
6
7
8
9
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
1549, 1564
1522, 1540
1525, 1555
1536
1524, 1545
1544
245 (11 200)
251 (13 400)
283 (9100)
239 (10 600)
234 (16 600)
248 (14 500)
227 (18 500)
252 (9200)
72–73a
138–140b
102–104
113–114c
162–165
111–112
97–99
110–111
244 (19 400)
227 (25 400)
10
131–132d
1541, 1556
a
b
c
d
Ref. [5] mp 71–73ЊC.
Ref. [10] mp 139ЊC.
Ref. [11] mp 111–113ЊC.
Ref. [11] mp 127ЊC.
3. Results and discussion
benzene ring is more sensitive to para-substituents;
the asymmetric band occurs at 1490–1570 cmϪ1
depending on the electronic properties of the second
group [12]. In the spectra of the compounds 1–10, the
frequencies of the N-nitro and C-nitro groups overlap
or are separated for 20–30 cmϪ1 only (see Table 3).
The equivocal assignment is not possible without 15N
labelling, however, the appearance of the C–NO2
band within 1520–1560 cmϪ1 indicates that the N-
methylnitramino group has the electron withdrawing
properties, comparable with those of halogens (cf.
Ref. [12]). In the region of the symmetric stretching
vibrations, the frequencies of the N-nitro (1280–
1300 cmϪ1) and C-nitro (1340–1350 cmϪ1) groups
can be distinguished according to the general rules;
this is well known that the bands of the former are
shifted towards lower wave numbers in respect to the
latter for ca. 50 cmϪ1 [13]. The only exception is the
nitramine 8, which displays the strong band at
1315 cmϪ1, i.e. outside of the typical region. In spite
of that, the final conclusion is that the number and
positions of the C-nitro groups do not influence the
frequencies of the N-nitro group which appear invari-
ably in the narrow regions of 1280–1300 and 1520–
3.1. Preparations
The compounds 1–10 are collected in Table 3. The
nitramines 1–9 were obtained from the corresponding
N-methylanilines by nitration with the mixed anhy-
dride (HNO3/Ac2O). The method, successfully
employed in the preparations of N-nitroazoles [9],
provides nitramines contaminated with N-acetyl deri-
vatives. The syntheses and purification of our
compounds were controlled using HPLC technique.
The nitramines 1 and 2 were rearranged in concen-
trated sulphuric acid, the isomers were separated
employing the flesh-chromatography method and N-
nitrated, as shown in Scheme 1.
N-Methyl-N-(3,5-dinitrophenyl)-nitramine (9) was
obtained from 3,5-dinitroaniline by the methylation.
and N-nitration in acetic anhydride. Tetryl (10) was
prepared from 2,4-dinitro-N-methylaniline by the
nitration with fuming nitric acid (d 1.52) in 80%
sulphuric acid.
3.2. Spectra
1560 cmϪ1
.
In the UV spectra, a strong (3.96 Ͻ log e Ͻ 4.40)
band with the maximum at 240–250 nm appears in
almost all cases; the only exception is the nitramine
3, where we observe a weak batochromic shift to
In the para-substituted N-methyl-N-phenylnitra-
mines, the asymmetric stretching vibration of the N-
nitro group lies in the narrow range of 1520–
1540 cmϪ1 [5]. The nitro group attached to the

Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
13
Scheme 1.
283 nm. Even if this weak batochromic shift is the
result of interaction between the parasubstituents, it
is not comparable with that observed in, e.g. N,N-
dimethyl-4-nitroaniline which absorbs in the visible
region. Consequently, we must conclude that the nitro
and nitramino groups are not the complementary
(donor and acceptor) ones.
6 Debye, the values calculated as the vector sum of
contributions from the C-nitro and nitramino groups
are even higher. The numbers collected in column A
were obtained assuming perpendicular conformation
of the nitramino group, with respect to the ring, and
the contribution of the C-nitro groups such as in nitro-
benzene [14]. In the case of sterically hindered substi-
tuents, it can be presumed that the contribution of the
C-nitro groups is decreased, due to the elimination of
the resonance interaction. In fact, the values in
column B are closer to the experimental ones; they
were obtained assuming that contributions of the C-
nitro groups are such as in nitromethane [15]. In the
case of 4 and 8, the agreement, between the calculated
3.3. Dipole moments, experimental
The experimental and calculated values of the
dipole moments of the title compounds are collected
in Table 4. The molecules (1–10) are intensely polar,
and their dipole moments exceed in some cases to

14
Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
Table 4
Dipole moments (in benzene, 25ЊC) of N-methyl-N-phenylnitramines substituted with the nitro groups (A: these values were calculated
assuming that the contribution from the N-methyl-N-phenylnitramine moiety is 4.34 Debye and that of the nitro group amounts 4.01 Debye,
the nitramino group is planar and perpendicular to the aromatic ring. B: the contribution of the nitro group in the vicinal position to the nitramino
or conjugated Ar-nitro group was diminished to 3.10 Debye due to the steric hindrance excluding conjugation [14])
No
Substituents
a
b
P2 (cm3)
mexp (Debye)
mcalc (Debye)
Dmcalc (Debye)
A
B
AM1
A
B
AM1
1
2
3
4
5
6
7
8
9
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
27.01
12.31
10.56
29.15
17.39
9.751
23.01
17.73
9.764
8.716
1.008
0.965
1.470
1.126
1.361
0.866
1.298
1.238
1.235
2.258
928.7
452.3
373.2
102.6
614.8
384.9
816.3
641.3
350.9
352.0
6.55
4.43
3.97
6.88
5.22
4.00
6.09
5.35
3.79
3.74
6.60
5.11
4.18
8.18
5.11
4.34
7.27
6.40
4.18
4.34
5.93
–
–
7.41
4.63
4.20
6.47
5.78
–
6.77
2.96
4.13
7.62
5.81
3.88
6.90
5.07
4.17
3.56
Ϫ0.05
Ϫ0.68
Ϫ0.21
Ϫ1.30
ϩ0.11
Ϫ0.34
Ϫ1.18
Ϫ1.05
Ϫ0.39
Ϫ0.60
ϩ0.62
–
–
Ϫ0.53
ϩ0.59
Ϫ0.20
Ϫ0.38
Ϫ0.43
–
Ϫ0.22
ϩ1.47
Ϫ0.16
Ϫ0.74
Ϫ0.59
ϩ0.12
Ϫ0.81
ϩ0.28
Ϫ0.38
ϩ0.18
10
3.96
Ϫ0.22
and experimental values, can be better (6.90 vs.
6.88 Debye) and 5.22 vs. 5.35 Debye) assuming that
both vicinal nitro groups are not conjugated with the
ring.
to the C–C–N–N torsion angle. Considering that
Dm ˆ Ϫ0:39 Debye in this case, we must conclude
that the interaction between substituents in 3 and 9
must be of inductive nature, if any.
The experimental dipole moment of 1 is nearly the
same as the value calculated, assuming perpendicular
conformation of the molecule, i.e. that the torsion
angle along the Ar–N bond amounts 90Њ. The result
seems to be reasonable for the first sight, considering
the steric hindrance around the nitramino group. The
high values of Dm in the case of 7 and 10 (the
compounds substituted in positions 2 and 6) indicate,
that the agreement between the experimental and
calculated values maybe rather incidental.
The results indicate the lack of any strong interac-
tions between the nitro and nitramino groups across
the ring, however, the Dm values are very large in
most cases. It prompted us to examine the molecular
structure of selected nitramines from the series,
employing the X-ray diffraction method. Our aim
was to calculate the dipole moments basing on the
factual geometry of these molecules.
3.4. Crystal structure
The calculated dipole moment of 2 exceeds the
experimental value for 0.68 Debye; in such a mole-
cule, the dipole moment must be very sensitive to its
conformation. Rotation of the methylnitramino group
by 10Њ from its perpendicular position decreases the
calculated value to 4.57 Debye (3.33 Debye when the
torsion angle along the Ar–N bond decreases from 90
to 60Њ placing the nitramino group far off the C-nitro
substituent). On the contrary, in the para substituted
nitramine 3, rotation along the C–N does not influ-
ence the dipole moment since the vector of the C-nitro
group is collinear with the rotation axis. The value
Dm ˆ Ϫ0:21 Debye may be, therefore, considered
as the moment of interaction between the nitro and
nitramino groups. However, the dipole moment of
symmetrically substituted 9 should be also insensitive
The following compounds have been selected for
crystal structure determination:
• N-methyl-N-(2,3-dinitrophenyl)-nitramine
characterised by the largest dipole moment;
• N-methyl-N-(3,5-dinitrophenyl)-nitramine
(4),
(9),
which possesses the second smallest experimental
dipole moment since the crystal structure of tetryl
(10) is known [15];
• N-methyl-N-(2,5-dinitrophenyl)-nitramine (6), to
compare its geometry with that of 4.
The molecular structures of 4, 6 and 9, showing the
atomic numbering scheme, are presented in Fig. 1(a)–
(c). The bond lengths and angles within the aromatic
rings and the nitramino groups are collected in Table

Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
15
5. The Table 6 contains the data on the geometry of
the C-nitro groups.
In further discussion we will compare mainly the
geometry of fist four compounds. The structure deter-
mination of tetryl has been carried out over 20 years
ago and before such a comparison it should be rede-
termined on modern facilities. The nitramino group is
almost planar, the atoms of the C2N–NO2 group are
situated on the same plane. The N(7)–N(8) bond is
˚
short (1.346(3)–1.360(2) A), indicating a high bond
order which is not influenced with the ring substitu-
ents. Consequently, the aromatic sextet and the nitra-
mine p-electron sextet are two independent sets of
multicenter orbitals, which are not conjugated to
each other. The mean torsion angle along the Ar–
NNO2 bond varies between 42.6 and 72.3Њ. In crystal
lattice, the nitramino group is therefore twisted from
the perpendicular position to the ring for ca. 18–47Њ.
Considering that the length of the Ar–NNO2 bond,
˚
1.417(2)–1.431(2) A, is close to the typical Car–NN
˚
single bond (1.43 A [16]); it may be concluded that
the C–C–N–N torsion angle is determined by the
weak intermolecular interactions in the crystal lattice.
The bond lengths and angles within the C-nitro
groups are typical of aromatic nitro compounds
[16]. The C–NO2 bond length equals to 1.466(3)–
˚
˚
1.476(2) A and it is for ca. 0.05 A longer than the
analogous C–N bond between the aromatic ring and
the nitramino group. Another interesting feature is the
torsion angle along the C–N bond of the Ar–NO2
group, as shown in Table 6. The para-nitro group in
3 is almost coplanar with the aromatic ring, so is the
meta-nitro group in 6. In the 9 molecule, both metha
nitro groups are slightly more twisted to the ring
plane: for 10.4 and 18.8Њ. The most overcrowded
nitramine 4 presents a rather peculiar geometry. The
C-nitro group in the orthoposition is perpendicular to
the ring while the meta nitro group is nearly coplanar
with the ring (9.3Њ).
The problem of conjugation between an aromatic
ring and the nitro substituents was studied by Holden
and Dickinson [17]. They have found that in most
cases, the nitro groups are deviated from coplanarity
Fig. 1. Molecular structure of: (a) N-methyl-N-(2,3-dinitrophenyl)-
nitramine (4); (b) N-methyl-N-(2,5-dinitrophenyl)-nitramine (6);
(c) N-methyl-N-(3,5-dinitrophenyl)-nitramine (9); showing atomic
numbering scheme. Thermal ellipsoids at 50% probability.

16
Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
Table 5
Selected structural parameters of the nitro derivatives of N-methyl-N-phenyl-nitramine; N-methyl-N-(4-nitrophenyl)-nitramine, N-methyl-N-
(2,3-dinitrophenyl)-nitramine (4), N-methyl-N-(2,5-dinitrophenyl)-nitramine (6), N-methyl-N-(3,5-dinitrophenyl)-nitramine (9) and N-methyl-
N-(2,4, 6-trinitrophenyl)-nitramine The geometry of the aromatic ring and the C-nitro groups
˚
Bond lengths (A) and angles (Њ) in the N-methyl-N-phenylnitramine derivatives
4 [4] 2,5 (6) 2,3 (4) 3,5 (9)
2,4,6 [15]
Aromatic ring
C(1)– C(2)
C(2)– C(3)
C(3)– C(4)
C(4)– C(5)
C(5)– C(6)
C(6)– C(1)
1.383(3)
1.390(2)
1.378(3)
1.394(2)
1.397
1.393
1.365
1.377
1.393
1.385
1.387(4)
1.379(4)
1.377(4)
1.389(4)
1.377(3)
1.372(3)
1.377(3)
1.368(3)
1.374(2)
1.375(2)
1.382(3)
1.375(4)
1.373(4)
1.368(4)
1.379(3)
1.378(2)
1.375(2)
1.373(2)
1.381(2)
1.388(2)
Nitramino groups
C(1)– N(7)
N(7)– N(8)
N(7)– C(11)
N(8)– O(9)
1.431(2)
1.346(3)
1.448(4)
1.238(3)
1.225(2)
1.422(2)
1.352(2)
1.445(3)
1.225(2)
1.223(2)
1.427(2)
1.360(2)
1.457(3)
1.224(2)
1.216(2)
1.417(2)
1.358(2)
1.459(2)
1.220(2)
1.222(2)
1.497
1.348
1.466
1.232
1.230
117.8
118.8
118.8
117.5
116.8
125.7
65
N(8)– O(10)
C(1)– N(7)– N(8)
C(1)– N(7)– C(11)
C(11)– N(7)– N(8)
N(7)– N(8)– O(9)
N(7)– N(8)– O(10)
O(9)– N(8)– O(10)
C–C–N–N (average)
118.8(2)
117.8(1)
116.4(2)
120.4(1)
122.0(2)
119.1(2)
117.8(2)
117.1(3)
125.1(2)
72.3
122.3(2)
119.6(2)
117.6(2)
117.0(2)
125.3(2)
63.9
120.2(2)
118.0(2)
116.9(2)
117.3(2)
125.7(2)
65.4
121.8(1)
117.0(1)
118.5(1)
117.6(1)
123.9(1)
42.6
Table 6
Selected structural parameters of the nitro derivatives of N-methyl-N-phenyl-nitramine; N-methyl-N-(4-nitrophenyl)-nitramine, N-methyl-N-
(2,3-dinitrophenyl)-nitramine (4), N-methyl-N-(2,5-dinitrophenyl)-nitramine (6), N-methyl-N-(3,5-dinitrophenyl)-nitramine (9) and N-methyl-
N-(2,4, 6-trinitrophenyl)-nitramine. The geometry of the Ar-nitro groups
˚
Bond lengths (A) and angles (Њ) in the N-methyl-N-phenylnitramine derivatives
4 [4]
para
2,5 (6)
meta
2,3 (4)
meta
3,5 (9)
meta
2,4,6 [15]
para
C–N
N–O
N–O
C–N–O
C–N–O
O–N–O
O–N–C–C (av.)
1.472(2)
1.221(2)
1.218(2)
1.476(2)
1.212(2)
1.212(2)
1.466(3)
1.207(3)
1.220(3)
1.467(2)
1.217(2)
1.216(2)
1.488
1.216
1.211
116.8
117.9
125.4
23
118.1(2)
118.0(2)
117.7(3)
118.0(1)
118.6(2)
123.2(2)
2.5
117.9(2)
124.1(2)
4.8
118.4(2)
123.9(3)
9.3
117.8(1)
124.1(1)
10.4
–
ortho
ortho
meta
ortho, ortho
C–N
N–O
N–O
C–N–O
C–N–O
O–N–O
O–N–C–C (av.)
–
–
–
–
–
–
–
1.465(2)
1.216(2)
1.211(2)
1.470(3)
1.203(3)
1.191(2)
1.472(2)
1.220(2)
1.214(2)
1.497, 1.485
1.214, 1.216
1.202, 1.213
116.9, 115.9
118.6, 117.2
124.5, 126.9
25, 44
119.5(2)
118.3(2)
117.7(1)
116.7(2)
123.8(2)
29.9
116.6(2)
125.0(3)
90.0
118.0(1)
124.3(1)
18.8

Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
17
with the aromatic ring due to the small value of the
in some cases.
stabilisation energy, emerging from the conjugation
between the nitro group and the aromatic sextet.
Consequently, the aromatic nitro substituent is not
so rigid as it used to be considered and some distor-
tions must be expected not only in a crystal lattice, but
also in solutions.
There is a strong separation of charges (^0.6e) in
the N-nitro group. Contrary to the mesomeric forms
presented above, the N(7) nitrogen atom is negatively
(Ϫ0.25e) charged on the expense of both substituents.
Such a charge distribution is consistent with the
results of more advanced QM studies carried out on
a simple model molecule [18,19]. It is responsible for
the contribution of the N-methyl-N-phenylnitramine
moiety into the dipole moments. The other source of
the dipole is the aryl nitro substituents, in which the
charge distribution is similar to that in the N-nitro
groups. It is not influenced with the torsion angles,
i.e. the partial charges on the nitrogen and oxygen
atoms are the same in coplanar and twisted groups.
The orientation of these vectors determines the
magnitude of the dipole moment. The estimated
value for 2 is significantly lower than calculated,
presuming perpendicular conformation, but much
higher than the dipole moment predicted (AM1) for
the optimised structure with the torsion angle of 118Њ
along the C(1)–N(7) bond. The result indicates that the
orientation of the nitramino group with respect to the
ring is statistical without any preferable conformation.
Rotation along the C–N bonds cannot account for
the large Dm values in the case of overcrowded nitra-
mines 4 and 7. There is a difference between the opti-
3.5. Dipole moments, calculated by the AM1 method
Considering large values of (Dm((Table 4, columns
A and B), we have calculated the dipole moments of
the nitramines 1–10 using the AM1 method [7]. The
compounds 3, 4, 6, 9 and 10, which molecular struc-
tures are known from the X-ray diffraction studies,
were examined first. We have assumed that the
conformations of the molecules in crystal lattices
are similar to those existing in diluted solutions in a
non-polar solvent. Consequently, the geometry opti-
misation of, e.g. nitramine 3, was started from the
conformation with the twisted nitramino group and
slightly distorted C-nitro groups, as given in Tables
5 and 6. It turned out that the optimal conformation of
the isolated molecule (3) is that with coplanar C-nitro
groups and the nitramino group twisted for 72Њ from
the ring plane. Its calculated dipole moment amounted
4.17 Debye and exceeded the experimental value for
0.38 Debye. The calculations of the remaining nitra-
mines were carried out assuming analogous geometry
of their molecules; the compound 8 is an exemplifica-
tion. It was presumed that the nitramino group and
either of the C-nitro groups were perpendicular to
the aromatic ring, while the second one remained
coplanar. The results of the calculations were the
same in both cases. The geometry optimisation estab-
lished the torsion angle along the C(1)–N(7) bond as
ca. 65Њ and demonstrated that both C-nitro groups are
arranged in a fan-like manner, twisted for ca. 40Њ from
the ring plane. The calculated dipole moment was the
same (5.07 Debye), and was smaller by 0.28 Debye
from the experimental value. The mean deviation of
the calculated from the experimental values is
0.2 Debye for ten compounds. The 2, 4 and 7 mole-
cules require a special consideration.
mised geometry of the
4 molecule and its
conformation in the crystal lattice. The C-nitro groups
are not twisted in parallel for ca. 45Њ (fan-like confor-
mation) as predicted by AM1, but the more hindered
one (at C-2) is perpendicular to the ring. This effect
cannot be responsible for the differences between the
calculated and estimated values of dipole moments.
Probably, in diluted solutions in non polar solvents,
the separation of positive and negative charges is
smaller when all the local dipoles are situated on the
same side of the molecule.
The semiempirical AM1 calculations point out
the source of large values of dipole moments of
the nitramines as well as the reasons of differ-
ences between the calculated and measured values
4. Conclusions
1. The nitramino group must be considered as the

18
Z. Daszkiewicz et al. / Journal of Molecular Structure 553 (2000) 9–18
individual functional group with the four-center
References
system of p-orbitals. It displays the electron with-
drawing properties due to the inductive effect.
There is no tendency to the conjugation between
the nitramine p-electrons and the aromatic sextet.
[1] W.N. White, C. Hathaway, D. Huston, J. Org. Chem. 35
(1970) 737.
[2] J.H. Ridd, E.F.V. Scriven, J. Chem. Soc., Chem. Commun.
(1972) 641.
2. The presence of nitro groups bound to the ring
does not significantly influence the geometry of
the nitramino moiety. The moment of the inter-
action do not increase with the increasing
number of nitro groups. The electron with-
drawing substituents on the ring do not disturb
the charge distribution within the nitramino
group.
[3] R. Anulewicz, T.M. Krygowski, R. Gawinecki, D. Rasal⁄a, J.
Phys. Org. Chem. 6 (1993) 257.
[4] K. Ejsmont, J.B. Kyziol⁄, Z. Daszkiewicz, M. Bujak, Acta
Cryst. C54 (1998) 672.
[5] Z. Daszkiewicz, E. Nowakowska, W.W. Prez˙do, J.B. Kyziol⁄,
Pol. J. Chem. 69 (1995) 437.
[6] G. Halvestrand, Z. Phys, Chem. B2 (1929) 428.
[7] J.J.P. Stewart, Win Mopac97, ver.2.0, Fujitsu Ltd, Tokyo,
Japan.
[8] G.M.Sheldrick,Shelx97,ProgramforSolutionandRefinement
3. Comparison of the calculated and estimated by
AM1 method dipole moments indicates small
energy barrier for the rotation of the nitramino
group in the absence of ortho substituents.
4. There is no sight of strong interaction of the
nitramino group with another NO2 substituent
across the aromatic ring. Consequently, the
influence of the NO2 substituents on the
susceptibility of the derivatives of N-methyl-
N-phenylnitramine to the acid catalysed rearran-
gement cannot be explained as the result of the
interaction of the migration origin with the
another group bonded to the ring.
¨
of Crystal Structure, University of Gottingen, Germany, 1997.
[9] P. Cohen-Fernandes, C.L. Habraken, J. Org. Chem. 36 (1971)
3084.
[10] E.D. Hughes, G.T. Jones, J. Chem. Soc. (1950) 2678.
[11] J. Glazer, E.D. Hughes, C.K. Ingold, A.T. James, G.T. Jones,
E. Roberts, J. Chem. Soc. (1950) 2657.
[12] M. Avram, Gh.D. Mateescu, Infrared Spectroscopy. Applica-
tions in Organic Chemistry, Wiley/Interscience, New York,
1972 (pp. 307–311).
[13] N.D. Colthup, L.H. Daly, S.E. Wiberley, Introduction to
Infrared and Raman Spectroscopy, Academic Press, New
York, 1964 (pp. 286–287).
[14] V.I. Minkin, O.A. Osipov, Y.A. Zhdanov, Dipolnye Momenty
v Organitscheskoy Khimii, Khimya Publication, Moskva,
1968 (p. 284).
[15] H.H. Cady, Acta Cryst. 23 (1967) 601.
[16] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G.
Orpen, R. Taylor, in: A.J.C. Wilson (Ed.), International Tables
for Crystallography, vol. C, Kluwer Academic, Dordrecht,
1995, pp. 685–706.
Acknowledgements
[17] J.R. Holden, C. Dickinson, J. Phys. Chem. 73 (1969) 1199.
[18] M.G. White, R.J. Colton, T.H. Lee, J.W. Rabalais, Chem.
Phys. 8 (1975) 391.
This work was supported by the Polish State
Committee for Scientific Research within the project
3 T 09A 156 18.
[19] B.J. Duke, J. Mol. Struct. 50 (1978) 109.