An ab initio and DFT study of radical addition reactions of imidoyl and thioyl radicals to methanimine

Abstract

Ab initio and DFT calculations reveal that both imidoyl and thioyl radicals add to the nitrogen end of methanimine through simultaneous SOMO-π*_imine, SOMO-π_imine, SOMO-LP_N and π*_radical-LP_N interactions between the radical and the imine. At the CCSD(T)/cc-pVDZ//BHandHLYP/cc-pVTZ level of theory, barriers of 13.8 and 26.1 kJ mol⁻¹ are calculated for the attack of the methylimidoyl radical at the carbon- and nitrogen- end of methanimine, respectively, indicating that the imidoyl radial has a preference for addition to the nitrogen end of imine. On the other hand, barriers of 25.1 and 13.4 kJ mol⁻¹ are calculated at the same level of theory for the addition reaction of the methanethioyl radical at the carbon- and nitrogen- end of methanimine, respectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO-π*_imine, SOMO-π_imine, SOMO-LP_N and π*_radical-LP_N interactions are worth 111, 89, 115 and 17 kJ mol⁻¹, respectively, in the transition state (4) for the reaction of methylimidoyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving all the radicals studied here. These multi-component interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions.