Transition state structure of the reaction of homolytic dissociation of the C-N bond and competition between dif erent mechanisms of the primary act of gas-phase monomolecular decomposition of nitrobenzene

Abstract

Various mechanisms of the primary act of gas-phase monomolecular thermal decomposition of nitrobenzene were studied theoretically. The following reactions were considered: radical decomposition with dissociation of the C-N bond, nitro-nitrite rearrangement to trans-phenyl nitrite and cis-phenyl nitrite, elimination of nitrous acid, as well as formation of 6(S)-7-oxa-8-azabicyclo[4.2.0]octa-1(8),2,4-triene 8-oxide were studied theoretically. Calculations were carried out for different temperatures using a number of density functional theory methods (B3LYP, wB97XD, CAM-B3LYP, MN12L, and PBE0) and basic sets (6-31G(d,p) and 6-31+G(2df,p)). The transition state of homolytic dissociation of the C-N bond was localized using the method of search for the structure corresponding to maximum value of the Gibbs free energy along the reaction coordinate. The structure thus found was used to evaluate the rate constants and the activation parameters at different temperatures. It was shown that not only radical decomposition, but also isomerization to trans-phenyl nitrite (at low temperatures) and cis-phenyl nitrite (at high temperatures) can contribute to the effective rate constant.