Heterocyclic free radicals. Part 8. The influence of the structure and the conformation of the side-chain on the properties of phenothiazine cation-radicals substituted at nitrogen

Abstract

In 10-substituted phenothiazine cation-radicals the extent of variation in nitrogen hyperfine splitting is greatest for purely hydrocarbon substituents and is reduced on introduction of polar functions into the alkyl group. It is concluded that the substituent effect is mainly a through-bond inductive effect of the classical kind. Substituents greater than methyl show strong preferences for particular conformations about the N–C bond. Variations in the ratio a(N) : a(3-H) are interpreted in terms of changes in the fold angle of the radicals occurring in response to changes of substituent type. Chiral substituents, as found in certain phenothiazine drugs, have characteristic effects on the e.s.r. spectra of the derived cation-radicals: two non-equivalent proton splittings arise from the β-CH₂ group.