Theoretical studies on intramolecular methyl migration in N-oxide radical cations

Based on the density functional theory (DFT), the intramolecular methyl migrations in a series of N-oxide radical cations (from M1 to M10) are analyzed in this paper. The calculations show that the intramolecular methyl migrations in all compounds are exothermic and that the activation energies vary from 21.6 to 30.8 kcal/mol. Either strong electron-withdrawing groups or strong electron-donating groups can promote the intramolecular methyl migration. Moreover, the author has supposed a new pathway in which formaldehyde forms, namely from the cleavage of trimethylamine oxide. This new pathway consists of three kinds of migrations: the electron transfer, the intramolecular methyl migration and the intramolecular proton transfer. Calculations of the activation energy indicate that the formation of trimethylamine oxide radical cation is beneficial to the intramolecular methyl migration. The findings are consistent with the fact that the reductive substance could promote the decomposition of trimethylamine oxide.