Enhanced Reactivity of RC≡CZ− (R = H and Cl; Z = O, S, and Se) and the Influence of Leaving Group on the α-Effect in the E2 Reactions

The enhanced reactivity exhibited by six pseudo-α-bases, RC≡CZ− (R = H and Cl; Z = O, S, and Se) in gas-phase E2 reactions with ethyl chloride was examined at the G2(+) level. It is found that anomalous reactivity is observed despite the fact that these chalcogen bases do not possess adjacent lone-pair electrons. The influence of the halide leaving groups on the α-effect and the origin of the α-effect in the E2 reactions of ethyl halides are investigated and discussed.