Investigations of structure and conformation. Part 7. Long-range interactions and line-width alternation associated with β- and γ-proton splittings in the e.s.r. spectra of radicals from cyclic ethers containing six-membered rings

Abstract

E.s.r. spectra from 1,3-dioxan-2-yl and 1,3,5-trioxanyl radicals at low temperatures show line-width alternation arising from conformational interconversion involving the rings. Both these radicals, which are pyramidal at the α-carbon atom, are found to have two pairs of γ-proton splittings of opposite sign, which accounts for the dramatic narrowing of the spectrum-width in each case as the temperature is raised: the contributions of hyperconjugation and of through-bond spin-polarization to spin transmission are discussed. Kinetic parameters are obtained for the chair–chair interconversion of the trioxanyl radical and also for 1,4-dioxanyl (the slow-exchange limit spectrum for which has been recorded). INDO calculations on these species are reported.