Molecular structures of mononitrophenols and their thermal decomposition tautomers

Abstract

The molecular structures of 2-nitro, 3-nitro, and 4-nitrophenol and their internal rotational isomers were calculated by an ab initio method using an HF/6-31G ∗ basis set. The nitro groups' position influenced the geometries. The perturbation of the hydroxyl group on the nitro group was observed in 2-nitrophenol which has a molecular structure distinct from that of the other two isomers. Among them, 2-nitrophenol is the most stable one. Tests of internal rotation of either the nitro or hydroxyl group of 3-nitro and 4-nitrophenol indicate that no significant deformations of the phenyl ring occurred after internal rotation; however, the internal rotational isomers of 2-nitrophenol differed from their original structure. As products of explosives induced by thermal or shock are of interest, four tautomers of 2-nitrophenol were selected to assess their geometries and energies. The calculations revealed that those products are thermodynamically unfavorable. Comparing calculated energies of 2-nitrophenol and 2-nitroaniline and their tautomers reveals that 2-nitrophenol more easily undergoes thermal decomposition than 2-nitroaniline. Results in this study provide valuable information regarding the sensitivity of aromatic nitrocompounds.