Nucleophilic addition/elimination on substituted methyl cations. Analysis of factors that affect thermochemistry and barrier heights

Abstract

The title reactions were shown by ab initio molecular orbital methods to occur via three step mechanisms: CH₂B ⁺+ AH → B–H₂C–AH⁺→⁺HB–H₂C–A → CH₂A⁺+ BH (all possible combinations of A = H, F, OH, NH₂ and B = H, F, OH, NH₂ were investigated). A p-donation stabilization constant for each group A and B, E_stab, is introduced. By applying these constants it is shown that a balance between the p-donation powers of B and A (expressed as E_stab[A]–E_stab[B]) regulates the well depths as well as the barrier heights. Simple expressions for the relationships between these quantities are derived.