Investigations of structure and conformation. Part V. Conformational interconversion and ring shape in five- and six-membered alicyclic radicals

Abstract

A conformational analysis is presented of a variety of radicals generated by reaction of the hydroxyl radical with A number of cyclopentane and cyclohexane derivatives. The β-hydrogen splittings in their e.s.r. spectra are interpreted in terms of a Bcos²θ dependence, where θ is the dihedral angle subtended by the β-C–H bond with the orbital of the unpaired electron. The results suggest that the cyclohexane-derived radical prefer a twisted-chair geometry except for 2-oxocyclohexyl which exists as a half-chair. The cyclopentyl-type radicals exist in a half-chair conformation except for the planar 2-oxocyclopentyl. A kinetic analysis for the conformational interconversion of 4-ammoniocyclohexyl and 2-oxocyclohexyl is reported.