REACTIVITY PARADIGMS - TRANSITION-STATE STRUCTURE, MECHANISMS OF BARRIER FORMATION, AND STEREOSPECIFICITY OF NUCLEOPHILIC SUBSTITUTIONS ON SIGMA-CATION RADICALS

The present work is concerned with odd electron reactivity and uses ab initio computations and VB mixing modeling to develop effective means for conceptualizing and predicting reactivity patterns in the nucleop hilic substitution reactions on sigma-cation radicals. All critical sp ecies along the reaction profile were characterized for both the backs ide and frontside substitution pathways. The backside and frontside tr ansition states (TSs) in the case of H2S + C2H6.+ were located also in two solvents. The computational data were then processed by a VB anal ysis which models the state of the reaction complex along the entire r eaction profile in terms of the contributing VB configurations. Subseq uently, the VB information was converted into VB mixing diagrams and r eactivity paradigms were formulated. The resulting analysis provides i nsight into the electronic structure and bonding in the TS as well as into the origins of the barrier and stereospecificity in nucleophilic substitutions on cation radicals. Mechanistic predictions are made and isotope effect probes developed for the stereochemistry and the elect ronic structure of the TSs.