Electron spin resonance study of free radicals generated from retinyl- and ionyl-derivatives

Free radicals generated from α- and β-ionyl bromides gave well resolved ESR spectra, but retinyl bromide and chloride gave only broad signals. Delocalised radicals were also spectrosopically observed on hydrogen abstraction from α-ionane, α-ionyltrimethylsilylether and buten-3-ynyl-2,6,6-trimethyl-2-cyclohexene. Retinyl and β-ionyl radicals, derived from the corresponding xanthates, were successfully spin trapped with nitrosodurene. The results suggested that the secondary sites C(7) and C(9) were the most reactive in the β-ionyl radical and that the secondary sites C(7) and C(11) and probably the primary site C(15) were the most reactive in the retinyl radical.