Theoretical studies on intramolecular methyl transfer in the 2-methoxy-pyridine derivative radical cations

Based on the density functional theory (DFT), the intramolecular methyl transfers in a series of 2-methoxy-pyridine derivative radical cations have been analyzed in this paper. The calculations indicate that all the methyl migrations are exothermic and the corresponding reaction enthalpies vary from −5.3 to −17.5 kcal/mol. In kinetics, the activation enthalpies vary from 35.9 to 48.9 kcal/mol. The electron-withdrawing substituting groups could promote the intramolecular methyl transfer, while the electron-donating substituting groups have the opposite effect. Meanwhile, the effects of substituting groups adjacent to the nitrogen atom are most significant. The Marcus theory analyses indicate that the major driving force for the acceleration effect of the substituent is the intrinsic factor. In addition, compared with other function groups, such as ethyl, isopropyl and phenyl groups, the methyl is the most difficult to transfer from oxygen atom to nitrogen atom in our systems.