The Vinylcyclopropane Radical Cation Rearrangement and Related Reactions on the C5H8•+Hypersurface

Abstract

The structures and major reaction pathways of the vinylcyclopropane radical cation and several of its derivatives are studied using highly correlated QCISD(T) and hybrid density functional calculations. Three different reactions have been studied: (i) the stereoisomerization via acyclic intermediates, (ii) the [1,3] methylene shift to form the cyclopentene radical cation involving either a concerted or a stepwise pathway, and (iii) the [1,2] hydrogen shift leading to either 1,4-pentadiene or 1,3-pentadiene radical cations. The activation energies for these processes are found to be quite similar, making the different pathways competitive. At the QCISD(T)//QCISD level of theory, an activation energy of 21.6 kcal/mol was calculated for the concerted pathway of the radical cationic vinylcyclopropane rearrangement, with the stepwise pathway only 1.9 kcal/mol higher in energy. With the exception of a small overestimation of the stabilization of the acyclic intermediates by homoconjugation, the results from the B3LYP method were in good agreement with the highly correlated reference calculations. Therefore, this computationally efficient method was used for the study of steric and electronic substituent effects on the electronic structure of the species involved and the overall shape of the hypersurface.