Reactions of alkyl free radicals with 4-vinylcyclohexene

Tertiary alkyl and cyanoalkyl free radicals prepared from t-butyl peroxypivalate and azobisisobutyronitrile were reacted with 4-vinylcyclohexene (1) for comparison with results previously obtained in the reaction of certain alkyl, alkoxy, peroxy, and thiyl radicals with this model olefin. The (CH3)3C• and (CH3)2(CN)C• radicals (like thiyl but in contrast to t-butoxy and t-butyl peroxy radicals) added to the vinyl double bond with subsequent abstraction of hydrogen by the resulting secondary alkyl radicals to give RH adducts along with higher molecular weight material.Vinylcyclohexenyl radicals formed by hydrogen abstraction from 1 reacted mainly by coupling to form dehydro dimers. They also formed substituted products by coupling with cyanoisopropyl radicals, but not with t-butyl radicals. The presence of both stabilized and unstabilized alkyl radicals of both secondary and tertiary types in these reactions with 1 permitted the observation of differences in the relative tendencies of these types of radicals to participate in addition, hydrogen abstraction, disproportionation, and coupling reactions. The observed effect of temperature (60 and 90°) on product distribution, together with estimated bond dissociation energies, suggest that the addition of cyanoisopropyl radicals to 1 is a reversible process.