Theoretical investigation of the reaction mechanism of atomic oxygen radical anion with pyridine

The reaction mechanism of atomic oxygen radical anion (O⁻) with pyridine (C₅H₅N) has been investigated at the G3MP2B3 level of theory. Three different entrance potential energy surfaces are explored, respectively, as atomic oxygen radical anion attacks γ-, β- and α-H atoms of pyridine. Possible thermodynamic product channels are examined subsequently. Based on the calculated G3MP2B3 energies and optimized geometries of all species for the title reaction, it has been demonstrated that the oxide anion formation channel is dominant, and the C₅H₃N⁻ + H₂O channel is also favorable in thermodynamics, whereas the H-abstraction and H⁺-abstraction channels are inaccessible at room temperature. The present conclusions are consistent qualitatively with the previous experimental results. The secondary reactions of the anionic products are expected to be responsible for the contradiction of branching ratios between present calculation and previous experiments.