HYDROLYSIS OF UNSUBSTITUTED AND ALKYL-SUBSTITUTED AZIRIDINIUM CATIONS- SELECTIVITY AND REACTION-MECHANISM (S(N)1 VS S(N)2)

The hydrolysis of unsubstituted, 2-methyl- and 2,2-dimethylaziridinium cations were studied by means of ab initio calculations (MP2/6-31G). Reactants, molecular clusters, transition states and products were op timized for each reaction path. In agreement with experimental data, t he hydrolysis reaction is found to be easier on the substituted carbon atom and the selectivity increases from the monomethyl- to the dimeth ylaziridinium cation. In addition, the transition state geometries sup port the previous suggestion of a change in the reaction mechanism in the disubstituted cation: the major product is formed through an S(N)1 -type transition state while an S(N)2 mechanism is at work in the othe r reactions.