ION-PAIR S(N)2 REACTIONS - THEORETICAL-STUDY OF INVERSION AND RETENTION MECHANISMS

Transition state structures have been found in ab initio calculations of identity reactions of lithium fluoride and chloride and of sodium c hloride with methyl fluoride and chloride. The retention transition st ate can be considered as an S(N)i type in which a methyl cation intera cts with a metal halide triple ion, MX(2)(-). The inversion transition states are highly bent from the linear X...C...X bond angles found fo r the ionic analogs. The inversion TS can also be considered as an ion ic assembly. These bond angles become more linear and the activation e nergies are reduced for reactions with ion pair aggregates; such trans ition states can be considered as a (XCH(3)X)(-) triple ion interactin g with a (MXM)(+) triple ion.