| Abstract
| - The complex potential energy surface for the unimolecular isomerization and dissociation of nitromethane(CH3NO2), including 10 CH3NO2 isomers, 46 interconversion transition states, and 16 major dissociationproducts, is probed theoretically at the G2MP2//B3LYP/6-311++G(2d,2p) level of theory. The geometriesand relative energies for various stationary points are determined and are in good agreement with the availableexperimental values. Based on the calculated G2MP2 potential energy surface, the possible nitromethaneunimolecular decomposition mechanism is discussed. It is shown that the most feasible decomposition channelsfor CH3NO2 are those that lead to 2CH3 + 2NO2, 2CH3O + 2NO, H2CO + HNO, and HCNO + H2O,respectively. Among them, 2CH3 and 2NO2 are produced by the direct C−N bond rupture of nitromethane,while the formation of the latter three products is initiated by CH3NO2 rearranging first to methyl nitrite orto aci-nitromethane. The C−N bond dissociation energy for nitromethane is calculated to be 61.9 kcal/mol,lower than the nitromethane → methyl nitrite and nitromethane → aci-nitromethane isomerization barriers by2.7 and 2.1 kcal/mol, respectively. Our results suggest that the CH3NO2 isomerization pathways are kineticallydisfavored in view of the relatively high activation barriers, in excess of 60 kcal/mol. The nitromethanedecomposition occurs either via the C−N bond rupture or via concerted molecular eliminations.
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