Molecular orbital studies of the isomers of 2,4,6-trinitrotoluene and some of its thermal decomposition products

The molecular structures of five positional isomers and three thermal decomposition products of 2,4,6-trinitrotoluene (TNT) were calculated by an ab initio HF/6-31G* method. During the determination of the structures of the positional isomers of TNT, the deformations of the phenyl ring and the distortions of the nitro and methyl groups were of primary concern. The calculations indicated that both of these were affected by the positions of the nitro groups. It was observed from the calculated energies that TNT was the most stable of the trinitrotoluene isomers. A comparison of the calculated energies of all the isomers revealed the tendency to form the stable isomer when the steric effects of the nitro groups were reduced. Although intramolecular hydrogen bonds existed in some molecules, their strengths were weak. The thermal decomposition products of explosives, induced by thermal or shock stimuli, are of major interest. Therefore we chose three thermal decomposition products of TNT in order to assess their geometries and energies. The calculations revealed that aci-TNT was thermodynamically unfavourable, whereas the nitrosoaromatic compound and anthranil were thermally favourable. (C) 1997 Elsevier Science B.V.