Theoretical study of nitro–nitrite rearrangement of CH 3 NO 2

Calculations designed to characterize the transition state and determine the barrier height for rearrangement of nitromethane to methyl nitrite are reported. Structures of CH 3 NO 2 , CH 3 ONO, dissociation products, CH 3 + NO 2 , and CH 3 O + 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 CH 3 and NO 2 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.