A G2(+) level investigation of the gas-phase non-identity SN2 reactions of halides with halodimethylamine

AbstractThe gas-phase non-identity SN2 reactions on nitrogen Y− + NMe2X → NMe2Y + X− (Y, X = F, Cl, Br, and I) were evaluated at the G2(+) level. The reactions are exothermic only when the nucleophile is the lighter halide. The complexation enthalpies for complexes Y−… Me2NX are found to correlate with electronegativity of X. Both central and overall barriers can be interpreted with the aid of Marcus equation. Kinetic and thermodynamic investigations predict that the nucleophilicity of X− decreases in the order: F− > Cl− > Br− > I− and the leaving-group ability increases in the order: F < Cl < Br < I