Exchange reactions of chloriranium and chlorirenium ions: a G2 investigation

Ab initio molecular orbital calculations at the G2 level have been used to study exchange reactions between cationic three-membered chlorine heterocycles and unsaturated hydrocarbons. The reactions are predicted to proceed with little or no overall barrier. The relationship of the theoretical findings to relevant experimental observations is discussed. The electronic characteristics of the exchange transition structures are compared with those for the analogous sulfur and phosphorus systems. The structures can be understood qualitatively in terms of a principal interaction resembling the triple-ion configuration found for S_N2 transition structures and a secondary back-bonding interaction.