Studies on Stable Free Radicals. II. Reactivity of Stable Nitroxide Radicals and NMR Spectra of Reaction Products

We have isolated coupled products of such stable free radicals as 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (II), cyclohexane-1-spiro-2′-(4′-oxoimidazolidine-l′-oxyl)-5′-spiro-l″-cyclohexane (IV) and 2,2,6,6-tetramethyl-4-oxopiperidine-1-thiyl derived from bis-[2,2,6,6-tetramethyl-4-oxopiperidyl-(1)]disulfide (VII) with a C-radical derived from α,α′-azo-bis(isobutyronitrile). The reactive site in these stable free radicals was studied from the structure of the coupled products. The homolysis of the disulfide (VII) appeared to be accelerated by an attack of the C-radical, 1-methyl-1-cyanoethyl. The NMR spectra of the products suggested a slow inversion of the nitrogen atom in piperidine derivatives.