2-Methyl-4,5-di­nitro­imidazole

The title compound, C₄H₄N₄O₄, is a stable energetic com­pound suitable for use as a propellant ingredient. There are two mol­ecules in the asymmetric unit, which differ in their nitro group out-of-plane torsion values.

Key indicators

• Single-crystal X-ray study
• T = 153 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.040
• wR factor = 0.080
• Data-to-parameter ratio = 11.9

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT432_ALERT_2_B Short Inter X...Y Contact  O13    ..  C4       =       2.87 Ang.

Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......       0.99
PLAT301_ALERT_3_C Main Residue  Disorder .........................       8.00 Perc.
PLAT432_ALERT_2_C Short Inter X...Y Contact  C2A    ..  O11'     =       3.00 Ang.
PLAT432_ALERT_2_C Short Inter X...Y Contact  C5     ..  O12'     =       2.95 Ang.

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   3 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion

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S1. Comment

Nitroimidazoles have been extensively studied because of their biological activity (Boyer, 1986); their syntheses are also of interest because they are stable energetic compounds, suitable for use as propellant and explosive ingredients (Bracuti, 1999). The title molecule, (I), contains an imidazole ring with a methyl and two nitro group substituents. The conformations of mono- and dinitroimidazoles were studied theoretically by Cho et al. (1998). When the nitro groups are on adjacent carbons, as in (I), the conformational potential energy surface is difficult to predict accurately. This is because the actual conformation is a compromise between a planar structure, which would maximize π-orbital conjugation, nd a structure with one or both nitro groups twisted out of plane, so as to minimize the electrostatic repulsion between neighboring nitro-group O atoms.

There are two molecules in the asymmetric unit of (I), one of which contains a disordered nitro group (Fig. 1). The first molecule without disorder adopts a pseudo-twofold conformation (with the local twofold axis down the C2—C2A methyl bond), wherein each nitro group twists approximately 19° out of the plane of the adjacent ring atoms. In the second molecule, the N15-nitro group is almost coplanar (+3.8° twist), while the N14-nitro group is disordered, and is either approximately −19° out of the plane in the major form [82.9 (5)% occupancy] or approximately 30° out-of-plane in the minor form [17.1 (5)% occupancy].

There are two short intermolecular N—H···N hydrogen bonds (Table 1). The crystal structure also contains several intermolecular contacts not involving H atoms which are less than the sum of van der Waals radii. Two of the shortest of these are near-perpendicular approaches between polar N—O bonds and C atoms in neighboring imidazole rings, suggesting a dipole–π-bond interaction. They are contacts O13···C4(1 − x, 1 − y, 1 − z) of 2.867 (3) Å and O12'···C5(1 − x, 1 − y, 1 − z) of 2.948 (5) Å; both distances are significantly less than the van der Waals contact distance of 3.22 Å (Rowland & Taylor, 1996). These short interactions are likely to have an attractive electrostatic component; the nitro group is considered to be one of the strongest electron-withdrawing substituents known when substituted on a π-bonded system. A third short intermolecular O···C distance is listed as the third entry in Table 1. Since it is between a methyl carbon atom and a nitro O atom, one might expect it to be due to C—H···O hydrogen bonding, but it has an extremely bent (105.7°) C—H···O angle. The contact is better described as a near-perpendicular approach of the N—O dipole to the C—C methyl bond; the N14—O11'···C2A angle is 151.0 (4)° and the C2—C2A···O11' angle is 90.6 (3)°.

S2. Experimental

The title compound, (I), was synthesized by P. Kasu and R. Damavarapu of the ARDEC (Dover, NJ, USA) by nitration of 2-methylimidazole. Crystals suitable for diffraction were grown by slow evaporation from a mixture of 2-butanone and octane. The solid displayed a ¹H NMR peak at 2.5 p.p.m. and a melting point of 480 K.

S3. Refinement

All H atoms were found in difference Fourier maps, but during the refinement the methyl H atoms were placed geometrically and allowed to ride on their parent C atoms, with C—H = 0.98 Å and U_iso = 1.5U_eq(C). Positional parameters of the amino H atoms were refined with U_iso = 1.2U_eq(N). Their N—H bond distances are 0.87 (2) and 0.92 (2) Å.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXTL (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of (I) with 25% atomic displacement ellipsoids. There are two molecules in the asymmetric unit. The occupation factors of the disordered nitro O atoms O11/O12 and O11'/O12' are 82.9 (5) and 17.1 (5)%, respectively.
	Fig. 2. A packing diagram of (I). The dashed lines that illustrate the N—H···N hydrogen bonds (Table 1) are more or less horizontal in this view. The dashed lines extending in the vertical direction are short non-bonded distances between nitro N···O dipoles and carbon atoms in adjacent aromatic imidazole rings.

2-methyl-4,5-dinitroimidazole

Crystal data

C4H4N4O4	Z = 4
Mr = 172.11	F(000) = 352
Triclinic, P1	Dx = 1.660 Mg m^−3
Hall symbol: -P 1	Melting point: 480 K
a = 7.9962 (9) Å	Mo Kα radiation, λ = 0.71073 Å
b = 8.2860 (9) Å	Cell parameters from 1898 reflections
c = 11.8913 (13) Å	θ = 2.7–26.3°
α = 70.702 (2)°	µ = 0.15 mm^−1
β = 71.205 (2)°	T = 153 K
γ = 72.983 (2)°	Plate, pale yellow
V = 688.50 (13) Å^3	0.45 × 0.1 × 0.03 mm

Data collection

Bruker SMART CCD area-detector diffractometer	2785 independent reflections
Radiation source: fine-focus sealed tube	1679 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.041
ϕ and ω scans	θmax = 26.4°, θmin = 1.9°
Absorption correction: integration (Wuensch et al., 1965)	h = −9→10
Tmin = 0.938, Tmax = 0.994	k = −10→10
4569 measured reflections	l = −14→14

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.040	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.080	w = 1/[σ^2(Fo^2) + (0.0255P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.86	(Δ/σ)max = 0.001
2785 reflections	Δρmax = 0.25 e Å^−3
235 parameters	Δρmin = −0.24 e Å^−3
5 restraints	Extinction correction: SHELXTL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0050 (13)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
N1	0.8940 (2)	0.2196 (2)	0.20523 (15)	0.0189 (4)
H1	0.960 (3)	0.114 (3)	0.2158 (18)	0.023*
C2	0.7130 (3)	0.2708 (3)	0.22442 (18)	0.0184 (5)
C2A	0.5899 (3)	0.1481 (3)	0.2679 (2)	0.0262 (6)
H2A	0.4931	0.1960	0.2248	0.039*
H2B	0.5373	0.1314	0.3566	0.039*
H2C	0.6574	0.0355	0.2512	0.039*
N3	0.6626 (2)	0.4438 (2)	0.20081 (15)	0.0191 (4)
C4	0.8173 (3)	0.5024 (3)	0.16654 (18)	0.0178 (5)
N4	0.8090 (3)	0.6884 (2)	0.13580 (16)	0.0211 (4)
O1	0.6626 (2)	0.78002 (19)	0.17204 (14)	0.0282 (4)
O2	0.9464 (2)	0.74345 (19)	0.07451 (14)	0.0281 (4)
C5	0.9627 (3)	0.3653 (3)	0.16913 (18)	0.0177 (5)
N5	1.1538 (2)	0.3484 (2)	0.14533 (16)	0.0216 (4)
O3	1.2104 (2)	0.4700 (2)	0.14601 (15)	0.0329 (4)
O4	1.2494 (2)	0.2093 (2)	0.12641 (14)	0.0290 (4)
N11	0.3169 (2)	0.6464 (2)	0.28355 (16)	0.0186 (4)
H11	0.427 (3)	0.577 (3)	0.2568 (18)	0.022*
C12	0.2349 (3)	0.7888 (3)	0.21075 (19)	0.0178 (5)
C12A	0.3055 (3)	0.8430 (3)	0.07509 (18)	0.0227 (5)
H12A	0.4046	0.9028	0.0550	0.034*
H12B	0.2085	0.9224	0.0378	0.034*
H12C	0.3500	0.7394	0.0429	0.034*
N13	0.0856 (2)	0.8707 (2)	0.27615 (15)	0.0187 (4)
C14	0.0741 (3)	0.7750 (3)	0.39412 (19)	0.0177 (5)
N14	−0.0754 (2)	0.8333 (2)	0.48947 (17)	0.0241 (5)
O11	−0.1591 (3)	0.9832 (3)	0.46445 (16)	0.0310 (7)	0.829 (5)
O12	−0.1150 (3)	0.7249 (3)	0.58908 (16)	0.0376 (8)	0.829 (5)
O11'	−0.2128 (7)	0.9227 (15)	0.4600 (5)	0.039 (4)*	0.171 (5)
O12'	−0.0449 (7)	0.8128 (13)	0.5895 (4)	0.029 (3)*	0.171 (5)
C15	0.2165 (3)	0.6346 (3)	0.40043 (18)	0.0179 (5)
N15	0.2718 (3)	0.4900 (2)	0.49712 (17)	0.0249 (5)
O13	0.1754 (3)	0.4717 (2)	0.60057 (15)	0.0493 (5)
O14	0.4153 (2)	0.3897 (2)	0.46713 (15)	0.0388 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0181 (11)	0.0145 (11)	0.0230 (10)	0.0012 (8)	−0.0074 (9)	−0.0052 (8)
C2	0.0172 (12)	0.0195 (13)	0.0183 (11)	0.0005 (10)	−0.0051 (10)	−0.0077 (10)
C2A	0.0203 (13)	0.0191 (13)	0.0382 (14)	−0.0018 (10)	−0.0075 (11)	−0.0081 (10)
N3	0.0171 (10)	0.0162 (10)	0.0238 (10)	0.0003 (8)	−0.0072 (8)	−0.0063 (8)
C4	0.0218 (13)	0.0145 (12)	0.0177 (12)	−0.0007 (10)	−0.0077 (10)	−0.0048 (9)
N4	0.0235 (12)	0.0182 (11)	0.0228 (10)	−0.0015 (9)	−0.0112 (9)	−0.0043 (8)
O1	0.0253 (9)	0.0166 (9)	0.0417 (10)	0.0027 (7)	−0.0099 (8)	−0.0108 (7)
O2	0.0237 (9)	0.0229 (9)	0.0343 (9)	−0.0077 (7)	−0.0063 (8)	−0.0015 (7)
C5	0.0171 (12)	0.0176 (12)	0.0186 (12)	−0.0028 (10)	−0.0055 (10)	−0.0049 (9)
N5	0.0197 (11)	0.0213 (11)	0.0242 (11)	−0.0022 (9)	−0.0081 (9)	−0.0059 (9)
O3	0.0278 (10)	0.0241 (10)	0.0550 (11)	−0.0060 (8)	−0.0172 (9)	−0.0136 (8)
O4	0.0190 (9)	0.0260 (10)	0.0434 (10)	0.0036 (7)	−0.0091 (8)	−0.0167 (8)
N11	0.0154 (10)	0.0160 (10)	0.0235 (10)	0.0010 (8)	−0.0060 (9)	−0.0066 (8)
C12	0.0185 (12)	0.0129 (12)	0.0232 (12)	−0.0037 (10)	−0.0076 (10)	−0.0034 (10)
C12A	0.0205 (13)	0.0176 (13)	0.0267 (13)	−0.0036 (10)	−0.0041 (10)	−0.0037 (10)
N13	0.0157 (11)	0.0172 (10)	0.0221 (10)	−0.0032 (8)	−0.0026 (9)	−0.0060 (8)
C14	0.0145 (12)	0.0191 (12)	0.0222 (12)	−0.0047 (10)	−0.0021 (10)	−0.0104 (10)
N14	0.0215 (11)	0.0251 (12)	0.0260 (11)	−0.0024 (9)	−0.0077 (9)	−0.0077 (9)
O11	0.0272 (13)	0.0229 (12)	0.0351 (12)	0.0073 (11)	−0.0066 (10)	−0.0097 (9)
O12	0.0376 (14)	0.0323 (14)	0.0289 (13)	−0.0042 (11)	0.0026 (10)	−0.0036 (10)
C15	0.0204 (13)	0.0179 (12)	0.0179 (11)	−0.0060 (10)	−0.0062 (10)	−0.0048 (9)
N15	0.0295 (12)	0.0245 (12)	0.0215 (11)	−0.0045 (10)	−0.0084 (10)	−0.0058 (9)
O13	0.0540 (13)	0.0521 (13)	0.0224 (9)	0.0074 (10)	−0.0050 (9)	−0.0053 (9)
O14	0.0370 (11)	0.0292 (10)	0.0354 (10)	0.0106 (9)	−0.0105 (9)	−0.0035 (8)

Geometric parameters (Å, º)

N1—C2	1.349 (3)	N11—C15	1.350 (3)
N1—C5	1.355 (3)	N11—H11	0.92 (2)
N1—H1	0.87 (2)	C12—N13	1.329 (3)
C2—N3	1.328 (2)	C12—C12A	1.485 (3)
C2—C2A	1.477 (3)	C12A—H12A	0.9800
C2A—H2A	0.9800	C12A—H12B	0.9800
C2A—H2B	0.9800	C12A—H12C	0.9800
C2A—H2C	0.9800	N13—C14	1.352 (2)
N3—C4	1.353 (3)	C14—C15	1.371 (3)
C4—C5	1.367 (3)	C14—N14	1.449 (3)
C4—N4	1.448 (3)	N14—O11	1.215 (2)
N4—O2	1.226 (2)	N14—O11'	1.216 (2)
N4—O1	1.226 (2)	N14—O12	1.237 (2)
C5—N5	1.434 (3)	N14—O12'	1.238 (2)
N5—O3	1.223 (2)	C15—N15	1.435 (3)
N5—O4	1.228 (2)	N15—O13	1.210 (2)
N11—C12	1.345 (2)	N15—O14	1.228 (2)
C2—N1—C5	107.61 (17)	N13—C12—N11	111.16 (18)
C2—N1—H1	128.9 (14)	N13—C12—C12A	125.75 (18)
C5—N1—H1	123.4 (14)	N11—C12—C12A	123.09 (19)
N3—C2—N1	110.92 (18)	C12—C12A—H12A	109.5
N3—C2—C2A	125.45 (19)	C12—C12A—H12B	109.5
N1—C2—C2A	123.62 (19)	H12A—C12A—H12B	109.5
C2—C2A—H2A	109.5	C12—C12A—H12C	109.5
C2—C2A—H2B	109.5	H12A—C12A—H12C	109.5
H2A—C2A—H2B	109.5	H12B—C12A—H12C	109.5
C2—C2A—H2C	109.5	C12—N13—C14	105.17 (17)
H2A—C2A—H2C	109.5	N13—C14—C15	110.29 (18)
H2B—C2A—H2C	109.5	N13—C14—N14	118.52 (18)
C2—N3—C4	105.37 (17)	C15—C14—N14	131.18 (18)
N3—C4—C5	110.45 (19)	O11—N14—O12	124.2 (2)
N3—C4—N4	119.38 (18)	O11'—N14—O12	109.5 (5)
C5—C4—N4	130.2 (2)	O11—N14—O12'	104.7 (4)
O2—N4—O1	124.73 (19)	O11'—N14—O12'	124.0 (3)
O2—N4—C4	118.35 (18)	O11—N14—C14	117.82 (18)
O1—N4—C4	116.91 (18)	O11'—N14—C14	117.6 (2)
N1—C5—C4	105.64 (19)	O12—N14—C14	117.87 (18)
N1—C5—N5	119.40 (18)	O12'—N14—C14	117.4 (2)
C4—C5—N5	135.0 (2)	N11—C15—C14	105.73 (18)
O3—N5—O4	124.64 (19)	N11—C15—N15	119.10 (18)
O3—N5—C5	118.91 (18)	C14—C15—N15	135.2 (2)
O4—N5—C5	116.44 (18)	O13—N15—O14	124.31 (19)
C12—N11—C15	107.65 (17)	O13—N15—C15	119.31 (19)
C12—N11—H11	124.5 (13)	O14—N15—C15	116.36 (18)
C15—N11—H11	127.6 (13)
C5—N1—C2—N3	0.7 (2)	N11—C12—N13—C14	−0.2 (2)
C5—N1—C2—C2A	−178.36 (19)	C12A—C12—N13—C14	179.4 (2)
N1—C2—N3—C4	−0.4 (2)	C12—N13—C14—C15	−0.1 (2)
C2A—C2—N3—C4	178.6 (2)	C12—N13—C14—N14	178.99 (17)
C2—N3—C4—C5	0.0 (2)	N13—C14—N14—O11	−16.5 (3)
C2—N3—C4—N4	−179.10 (17)	C15—C14—N14—O11	162.4 (3)
N3—C4—N4—O2	−160.59 (18)	N13—C14—N14—O11'	25.5 (8)
C5—C4—N4—O2	20.5 (3)	C15—C14—N14—O11'	−155.6 (8)
N3—C4—N4—O1	18.3 (3)	N13—C14—N14—O12	160.0 (2)
C5—C4—N4—O1	−160.6 (2)	C15—C14—N14—O12	−21.1 (3)
C2—N1—C5—C4	−0.6 (2)	N13—C14—N14—O12'	−143.2 (6)
C2—N1—C5—N5	178.42 (17)	C15—C14—N14—O12'	35.7 (7)
N3—C4—C5—N1	0.4 (2)	C12—N11—C15—C14	−0.4 (2)
N4—C4—C5—N1	179.38 (19)	C12—N11—C15—N15	178.33 (18)
N3—C4—C5—N5	−178.4 (2)	N13—C14—C15—N11	0.3 (2)
N4—C4—C5—N5	0.5 (4)	N14—C14—C15—N11	−178.62 (19)
N1—C5—N5—O3	−160.23 (18)	N13—C14—C15—N15	−178.1 (2)
C4—C5—N5—O3	18.5 (3)	N14—C14—C15—N15	2.9 (4)
N1—C5—N5—O4	19.2 (3)	N11—C15—N15—O13	−174.6 (2)
C4—C5—N5—O4	−162.0 (2)	C14—C15—N15—O13	3.7 (4)
C15—N11—C12—N13	0.4 (2)	N11—C15—N15—O14	3.9 (3)
C15—N11—C12—C12A	−179.23 (19)	C14—C15—N15—O14	−177.8 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···N13^i	0.87 (2)	1.97 (2)	2.837 (2)	168.1 (19)
N11—H11···N3	0.92 (2)	1.92 (2)	2.837 (2)	176.9 (19)
C2A—H2B···O11′^i	0.98	2.58	2.996 (4)	106

Symmetry code: (i) x+1, y−1, z.