Density functional study of the decomposition pathways of nitroethane and 2-nitropropane

Abstract

Some properties of the decomposition pathways of nitroethane (1) and 2-nitropropane (2) were studied computationally at the B3LYP/6-311+G(3df,2p) level. It was found that the concerted molecular elimination (CME) pathway is the most favourable decomposition channel, but other eventually important mechanistic routes were also investigated. It was found that the CME of HONO in both nitroalkanes proceeds through relatively high barriers, 42.0 kcal mol⁻¹ and 39.2 kcal mol⁻¹ for 1 and 2 respectively. These values agree well with the activation energies predicted by Benson and co-workers on the basis of experimental information. The enthalpies of formation of 1 and 2 were also determined, both applying the G3 model chemistry to the atomisation reactions on the one hand, and the G3 and B3LYP methods to isodesmic reactions involving nitromethane on the other. Supporting evidence was found that the enthalpies of formation calculated in this way for 1, −24.5 ± 1 kcal mol⁻¹, and 2, −34.0 ± 1 kcal mol⁻¹, are indeed accurate enough for practical purposes. The accuracy of the density functional calculations is discussed at the light of the available experimental results.