Polymorphism of 1-methyl-2-nitro-5-vinylimidazole.

Three polymorphic forms of 1-methyl-2-nitro-5-vinylimidazole, a potential antimicrobial drug, have been isolated and characterized by thermomicroscopy, differential scanning calorimetry, infrared spectroscopy and X-ray powder diffraction. On the basis of some infrared bands, the hypothesis has been made that the different packing of forms I and II was due to the existence of the molecule in two different conformations in the two forms. The direct confirmation of the hypothesis has been sought by X-ray diffraction of single crystals, but a suitable crystal was obtained only for form II. Form II is orthorhombic, space group Pbca, with unit-cell dimensions: a = 13.05, b = 10.83, c = 10.21 A; Z = 8. From the X-ray analysis, carried out by direct methods, the molecule is planar and the vinyl group is cisoid to the heterocyclic CH group. Then, the existence of the molecule as transoid conformation in form I still remains a hypothesis.