1,3-Bis(ethylamino)-2-nitrobenzene, 1,3-bis(n-octylamino)-2-nitrobenzene and 4-ethylamino-2-methyl-1H-benzimidazole.

1,3-Bis(ethylamino)-2-nitrobenzene, C(10)H(15)N(3)O(2), (I), and 1,3-bis(n-octylamino)-2-nitrobenzene, C(22)H(39)N(3)O(2), (II), are the first structurally characterized 1,3-bis(n-alkylamino)-2-nitrobenzenes. Both molecules are bisected though the nitro N atom and the 2-C and 5-C atoms of the ring by twofold rotation axes. Both display intramolecular N-H...O hydrogen bonds between the amine and nitro groups, but no intermolecular hydrogen bonding. The nearly planar molecules pack into flat layers ca 3.4 A apart that interact by hydrophobic interactions involving the n-alkyl groups rather than by pi-pi interactions between the rings. The intra- and intermolecular interactions in these molecules are of interest in understanding the physical properties of polymers made from them. Upon heating in the presence of anhydrous potassium carbonate in dimethylacetamide, (I) and (II) cyclize with formal loss of hydrogen peroxide to form substituted benzimidazoles. Thus, 4-ethylamino-2-methyl-1H-benzimidazole, C(10)H(13)N(3), (III), was obtained from (I) under these reaction conditions. Compound (III) contains two independent molecules with no imposed internal symmetry. The molecules are linked into chains via N-H...N hydrogen bonds involving the imidazole rings, while the ethylamino groups do not participate in any hydrogen bonding. This is the first reported structure of a benzimidazole derivative with 4-amino and 2-alkyl substituents.