Semi-empirical MNDO-SCF study of the molecular and electronic structures of some permethylated σ* radicals

Abstract

Molecular and electronic structures have been calculated, using the MNDO method, for a range of permethylated σ* radicals, of general constitution Me_nM[graphic omitted]M′Me_n′. When M = M′, radicals based upon second-row M are all calculated to be genuine σ* radicals, but when M is a first-row element, all the systems studied except for Me₆C₂^– are calculated to be very weak complexes of Me_nM: and Me_n˙ having long M ⋯ M distances; Me₆C₂^– is calculated to dissociate completely to Me₃C^– and Me₃C˙. When M ≠ M′ and M is a first-row element and M′ is a second-row element, genuine σ* radicals are formed only when M and M′ are together of low electronegativity: high electronegativity of M and M′ leads either to weak complexes of Me_nM: + Me_n′M′˙ or to complete dissociation.