Theoretical study of nitro–nitrite rearrangement of CH3NO2

Abstract

Calculations designed to characterize the transition state and determine the barrier height for rearrangement of nitromethane to methyl nitrite are reported. Structures of CH3NO2, CH3ONO, dissociation products, CH3 + NO2, and CH3O + NO, and the transition state for nitro–nitrite rearrangement have been optimized at the MCSCF/4-31G level. The geometry of the transition state may be approximately described as separated CH3 and NO2 species with extremely long C—N and C—O bond lengths, 3.396 and 3.654 Å, respectively. Energies have been obtained by large-scale multireference single- and double-excitation CI calculations (6-31G* basis). The transition state is calculated to lie 56.7 kcal/mol above nitromethane (with zero-point energy). A C—N bond dissociation energy of 51.7 kcal/mol is obtained. Results are compared with the infrared multiphoton dissociation experiment of Wodtke, Hintsa, and Lee. Keywords: nitromethane, abinitio calculations, transition state, rearrangement, dissociation.