2,4,6-Trimethyl-N-nitro-aniline

Article abstract of DOI:10.1107/S0108270106055776

In 2,4,6-trimethyl-N-nitro-aniline (alternatively called mesitylnitramine), C9H12N2O2, the primary nitramino group is planar with a short N - N bond and is nearly perpendicular to the aromatic ring. The methyl group located in the para position is disorde

Full text of DOI:10.1107/S0108270106055776

organic compounds
Acta Crystallographica Section C
Crystal Structure
the differences in the lengths of the ArÐN bonds. In pyridine
Ê
derivatives (III) and (IV), these bonds are more than 0.05 A
Communications
shorter (Zaleski et al., 2001) than in (I). This may be inter-
preted as the result of a change in the ꢀ-electron distribution
within the nitramino group, under the in¯uence of the elec-
tron-de®cient ring.
ISSN 0108-2701
2,4,6-Trimethyl-N-nitroaniline
The conformations of the molecules con®rm this conclu-
sion. In (I), the torsion angle along the C1ÐN7 bond (ca
83.7ꢀ) may be caused by the steric hindrance, but in (II), the
nitramine group is twisted by approximately 22 and 44ꢀ for the
two independent molecules (Zaleski et al., 2002). In contrast,
in (III) and (IV), the nitramine groups are nearly coplanar
with the pyridine ring, indicating conjugation between both ꢀ-
electron systems. The geometry of the aromatic ring in (I) is
not disturbed by the relatively large number of substituents.
The difference between a particular CÐC bond length and the
Janusz Kyzioø, Zdzisøaw Daszkiewicz and Jacek Zaleski*
Institute of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland
Correspondence e-mail: zaleski@uni.opole.pl
Received 9 October 2006
Accepted 21 December 2006
Online 23 January 2007
Ê
Ê
average value (1.388 A) does not exceed 0.007 A. At room
temperature, the methyl group in the para position rotates
along the CÐC axis, this being observed as a splitting of the
H-atom positions. A decrease of the temperature causes
destruction of the crystal as a result of a phase transition.
In the IR spectrum of (I), a strong and broad band, with the
maximum at 3226 cm 1, indicates the presence of a hydrogen
bond. Despite the acidic properties of primary nitramines, the
interaction is weak, as indicated by the long donor±acceptor
distance (Table 2). The molecules are joined together along
the a axis via the hydrogen bond, but ꢀ±ꢀ stacking interactions
seem to be a decisive factor in the molecular packing (Fig. 2).
The molecules are arranged parallel in columns. Each moꢀl-
In 2,4,6-trimethyl-N-nitroaniline (alternatively called mesityl-
nitramine), C9H12N2O2, the primary nitramino group is planar
with a short NÐN bond and is nearly perpendicular to the
aromatic ring. The methyl group located in the para position is
disordered, each H atom having half-occupancy. The mol-
ecules are linked together along the [100] axis by inter-
molecular NÐHÁ Á ÁO hydrogen bonds.
Comment
A common feature of primary and secondary N-aryl-
nitramines is their ability to rearrange to the corresponding
ortho and para amino±nitro compounds under the in¯uence of
an acid (Banthorpe & Thomas, 1965). The molecular struc-
tures of N-methyl-N-phenylnitramine and its ring-substituted
derivatives are well elucidated. The geometric parameters of
the nitramino group, in particular a long ArÐN bond, a short
NÐN bond and a large torsion angle on the ArÐN bond, are
not in¯uenced by the ring substituents (Daszkiewicz et al.,
2000, 2002). The results were unexpected since migration of
the N-nitro group to the ring requires a nearly coplanar
conformation of the nitramine molecule. The geometry of the
primary nitramino group has not been so frequently studied,
and in most examples the NHNO2 group is connected to an
electron-de®cient ring, as in mesitylnitramines (III) and (IV).
Ê
ecule is 3.524 (2) A from its neighbours and twisted by 180 .
The angle between the molecules belonging to neighbouring
stacks is 41.4 (11)ꢀ. In the crystal network of (II), the hydrogen
bond is addressed to the p-nitro group (Zaleski et al., 2002).
Comparison of (I) and (II) indicates that the O atom of the
nitramine group is a very poor H-atom acceptor. Analogously,
the crystal structure of N,N-dinitroethylenediamine is deter-
mined by the local dipole±dipole interactions in spite of the
Ê
weak (3.007 A) NÐHÁ Á ÁO hydrogen bond (Turley, 1968).
The geometries of primary and secondary N-arylnitramines
are similar in the most characteristic aspects. In (I), the
The nitramino group in (I) (Fig. 1) is nearly planar, and the
sum of the valence angles [358.0 (12)ꢀ] around atom N7
indicates trigonal hybridization of the amide N atom.
However, atom N7 deviates from the C1/H7/N8 plane by
Ê
0.100 (2) A. The torsion angle along the NÐN bond is small at
4.4 (11)ꢀ (averaged) and may result from non-valence inter-
actions. The N7ÐN8 bond length (Table 1) also indicates high
bond order. The differences with respect to nitramines (II)±
Figure 1
The molecular structure of (I). Displacement ellipsoids are drawn at the
50% probability level and H atoms are shown as small spheres of
arbitrary radii.
Ê
(IV) are small [0.025 (1) A maximum] but they correspond to
o126 # 2007 International Union of Crystallography
DOI: 10.1107/S0108270106055776
Acta Cryst. (2007). C63, o126±o128

organic compounds
Crystal data
environment of amide atom N7 indicates its trigonal hybridi-
zation and high NÐN bond order. The planar nitramino group
is bonded to the benzene ring with a relatively long CÐN
bond and twisted with respect to the nearly perpendicular
position. Such a conformation is an effect of a steric inter-
action between N±methyl or Ar±methyl groups and the
neighbouring substituent.
C9H12N2O2
Mr = 180.21
Orthorhombic, Pbca
Ê
a = 7.6217 (6) A
b = 15.8538 (13) A
Z = 8
Dx = 1.210 Mg m
3
Mo Kꢃ radiation
1
ꢄ = 0.09 mm
T = 295 (2) K
Ê
Ê
c = 16.3696 (12) A
Ê
V = 1978.0 (3) A
Plate, colourless
0.30 Â 0.25 Â 0.15 mm
3
Data collection
Oxford Diffraction Xcalibur
diffractometer
! scans
14835 measured re¯ections
2650 independent re¯ections
1329 re¯ections with I > 2ꢅ(I)
Rint = 0.038
ꢆmax = 29.6ꢀ
Re®nement
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.046
wR(F2) = 0.142
S = 0.98
2650 re¯ections
136 parameters
H atoms treated by a mixture of
independent and constrained
re®nement
w = 1/[ꢅ2(F2o) + (0.0662P)2]
where P = (F2o + 2Fc2)/3
(Á/ꢅ)max = 0.018
3
Ê
Áꢇmax = 0.14 e A
3
Ê
0.18 e A
Áꢇmin
=
Table 1
Selected geometric parameters (A, ).
ꢀ
Ê
C1ÐC2
C1ÐC6
C1ÐN7
C2ÐC3
C3ÐC4
C4ÐC5
1.393 (2)
1.394 (2)
1.4310 (19)
1.387 (2)
1.385 (3)
1.381 (3)
C5ÐC6
N7ÐN8
N7ÐH7
N8ÐO10
N8ÐO9
1.387 (2)
1.3405 (17)
0.874 (18)
1.2173 (16)
1.2290 (17)
Figure 2
The packing of mesitylnitramine, viewed down c, showing the hydrogen-
bonding scheme (dashed lines). Displacement ellipsoids are drawn at the
50% probability level.
C2ÐC1ÐC6
C3ÐC2ÐC1
C4ÐC3ÐC2
C5ÐC4ÐC3
C4ÐC5ÐC6
C5ÐC6ÐC1
122.75 (14)
117.15 (16)
122.05 (17)
118.77 (16)
121.91 (18)
117.36 (15)
N8ÐN7ÐC1
N8ÐN7ÐH7
C1ÐN7ÐH7
O10ÐN8ÐO9
O10ÐN8ÐN7
O9ÐN8ÐN7
120.47 (13)
114.7 (12)
122.8 (12)
124.40 (14)
118.92 (14)
116.64 (14)
Experimental
Ethyl bromide (2.3 ml, 30 mmol), diluted with absolute diethyl ether
(15 ml), was added dropwise to a stirred suspension of magnesium
turnings (1.20 g, 50 mmol) in ether (50 ml). A solution of ethyl
magnesium bromide was ®ltered into 2,4,6-trimethylaniline (2.70 g,
20 mmol) dissolved in dry toluene (100 ml). The mixture was stirred
and re¯uxed for 1 h. It was cooled to room temperature, n-butyl
nitrate (3.60 g, 30 mmol) was added and stirring was continued for
1 h. Water (30 ml) and acetic acid (2 ml) were added to the mixture,
and the aqueous layer was separated and discarded. The nitramine
was extracted (3 Â 30 ml) from the ethereal solution with 1 M
aqueous potassium hydroxide and precipitated by careful acidi®ca-
tion (273 K) with 3 M hydrochloric acid. The crude product was
collected by ®ltration, dried in a vacuum and crystallized from n-hex-
ane. N-(2,4,6-Trimethylphenyl)nitramine (1.60 g, 44%) was obtained
as colourless crystals, melting at 386±388 K. Crystals suitable for
X-ray diffraction studies were obtained by slow evaporation of a 1:1
n-hexane±diethyl ether solution at room temperature. IR (KBr, ꢁ,
cm 1): 3226 (NH proton, stretching vibrations); 1593, 1326 (NÐNO2,
asymmetric and symmetric stretch). 1H NMR (CDCl3): ꢂ 9.58 (s, 1H,
nitramine H atom), 6.95 (s, 2H, aromatic H atoms), 2.30 (s, 3H, para-
methyl group), 2.24 (s, 6H, ortho-methyl groups). 13C NMR (CDCl3):
ꢂ 140.7 (C-1), 137.1 (C-2 and C-6), 129.6 (C-3 and C-5), 129.4 (C-4),
21.3 (para-CH3), 17.9 (ortho-CH3).
C2ÐC1ÐN7ÐN8
C6ÐC1ÐN7ÐN8
84.18 (19)
96.85 (18)
C1ÐN7ÐN8ÐO10
C1ÐN7ÐN8ÐO9
5.5 (2)
176.74 (15)
Table 2
Hydrogen-bond geometry (A, ).
ꢀ
Ê
DÐHÁ Á ÁA
N7ÐH7Á Á ÁO9i
Symmetry code: (i) x 12; y; z ‡ 21.
DÐH
HÁ Á ÁA
2.080 (19)
DÁ Á ÁA
DÐHÁ Á ÁA
0.874 (18)
2.9320 (18)
164.6 (17)
The H atoms of the benzene ring and the H atom bonded to N7
were re®ned freely; the CÐH bond lengths are 0.937 (17) and
Ê
Ê
0.941 (18) A, and the NÐH bond length is 0.874 (18) A. The H atoms
of the CH3 groups were placed in calculated positions (CÐH =
Ê
0.98 A). The methyl group in the para position is disordered, with a
site-occupation factor of 0.5.
Data collection: CrysAlis CCD (Oxford Diffraction, 2002); cell
re®nement: CrysAlis RED (Oxford Diffraction, 2002); data reduc-
tion: CrysAlis RED; program(s) used to solve structure: SHELXS97
(Sheldrick, 1997); program(s) used to re®ne structure: SHELXL97
(Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1990);
software used to prepare material for publication: SHELXL97.
Differential scanning calorimetry studies showed that mesityl-
nitramine undergoes a strong ®rst-order phase transition at 230 K on
1
cooling and at 270 K on heating, with ÁH = 0.4 kJ mol and ÁS =
1.6 J K mol 1. The single crystal is destroyed and appears as a
powder at the phase transition.
ꢁ
Acta Cryst. (2007). C63, o126±o128
Kyzioø et al. C9H12N2O2 o127

organic compounds
Daszkiewicz, Z., Zaleski, J., Nowakowska, E. M. & Kyzioø, J. B. (2002). Pol. J.
Chem. 76, 1113±1125.
Oxford Diffraction (2002). CrysAlis CCD (Version 1.170) and CrysAlis RED
(Version 1.170.16). Oxford Diffraction, Wrocøaw, Poland.
Sheldrick, G. M. (1990). SHELXTL. Siemens Analytical X±ray Instruments
Inc., Madison, Wisconsin, USA.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: HJ3024). Services for accessing these data are
described at the back of the journal.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of
È
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ꢁ
o128 Kyzioø et al. C9H12N2O2
Acta Cryst. (2007). C63, o126±o128