Quantum chemical calculations on the structure and conformation of substituted ethylene radical cations and on their ESR spectra

Abstract

The geometries and conformations of a series of radical cations, derived from ethylene by mono- and distribution with OH or OCH 3 groups and CH 3 groups, have been determined by ab initio methods and by the INDO method. The calculated barriers to rotation around the CC bonds vary from 35 kJmol −1 for the 1,1-dimethoxyethylene radical cation to over 75–100 kJ mol −1 in monosubstituted derivatives and up to 230 kJ mol −1 for the 1,2-dimethoxyethylene radical cation; an explanation for this variation is provided by analysis of the charge and spin density. The calculated proton hyperfine coupling constants agree well with experimental values. In some cases, it was necessary to take the influence of the barriers to rotation into account explicitly by conformational averaging.