2-Chloro-4-nitro-1H-imidazole

The molecule of the title compound, C3H2ClN3O2, is almost planar; the dihedral angle between the imidazole ring and the nitro group is 1.7 (2)°. In the crystal structure, pairs of intermolecular C—H⋯O hydrogen bonds link inversion-related molecules into dimers, generating R 2 2(10) ring motifs. The dimers are interconnected into two-dimensional networks parallel to (102) via intermolecular N—H⋯N hydrogen bonds. Further stabilization is provided by short intermolecular Cl⋯O interactions [3.142 (2) and 3.1475 (19) Å].

The molecule of the title compound, C 3 H 2 ClN 3 O 2 , is almost planar; the dihedral angle between the imidazole ring and the nitro group is 1.7 (2) . In the crystal structure, pairs of intermolecular C-HÁ Á ÁO hydrogen bonds link inversionrelated molecules into dimers, generating R 2 2 (10) ring motifs. The dimers are interconnected into two-dimensional networks parallel to (102) via intermolecular N-HÁ Á ÁN hydrogen bonds. Further stabilization is provided by short intermolecular ClÁ Á ÁO interactions [3.142 (2) and 3.1475 (19) Å ].

Comment
The nitro aromatic compounds are used as key substrates for the preparation of useful materials such as dyes, pharmaceuticals, perfumes and plastics (Susanta et al., 2000). Therefore, nitration of hydrocarbons particularly of aromatic compounds is probably one of the most widely studied organic reactions (Jadhav et al., 2008). In addition, they have proven to be valuable reagents for the synthesis of complex target molecules (Kolavi et al., 2006). Most of the substituted imidazoles are widely used in pharmaceutical ingredients (Clark & Macquarrie, 1996). The imidazole nucleus is one of the important heterocyclic groups due to its presence in a large number of bioactive pharmaceutical and agrochemicals (Anuradha et al., 2006). It was also reported that a large number of compounds containing the imidazole ring possess some moderately useful activities.
The environmentally friendly nitration reaction has been the focus of recent research.
In the title imidazole derivative, the 1H-imidazole ring with atom sequence C1/N1/C2/C3/N2 is essentially planar, with a maximum deviation of 0.003 (2) Å at atom N1. The nitro group is coplanar with the attached 1H-imidazole ring, as indicated by the dihedral angle of 1.7 (2)°. The geometric parameters agree well with those reported for related 4-nitroimidazole structures (Ségalas et al., 1992;De Bondt et al., 1993).

Experimental
Nitronium tetrafluoroborate (1.42 g, 0.0107 mol) was dissolved in nitromethane (10 ml) and 2-chloroimidazole (1 g, 0.0097 mol) was then added in lot-wise. The reaction mixture was stirred at room temperature for 3 h. The reaction mixture was then neutrallized with an aqueous solution of sodium bicarbonate. The separated solid was then filtered. The crude product was purified by column chromatography using 60-120 silica gel. The fraction eluted at 10 % ethyl acetate in hexane was concentrated to afford the title compound as pale yellow single crystals (Yield 0.9 g, 62.93 %; m.p. 363-366 K).

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.