Ab initio studies of the molecular structures of dinitrotoluenes

The molecular structures of six positional dinitrotoluene isomers were calculated by an ab initio HF/6-31G* method. Different deformations of the phenyl ring and distortions of the nitro and methyl groups with the ring of each isomer were observed. Deformations of the benzene ring did not completely match the rule predicted by Domenicano et al. In addition to the inductive and resonance effects, steric effects also play an influential role in the deformation of the phenyl ring and the distortion of the substitution groups with the ring. Calculated energies indicated that of all the dinitrotoluene isomers 3,5-dinitrotoluene is the most stable molecule and 2,3-dinitrotoluene is the most unstable. Comparison of the calculated energies of all isomers revealed a tendency that a stable isomer is found when the steric effect is reduced. Intramolecular hydrogen bonds were also analyzed for some isomers; their strengths were, however, found to be weak.