The effect of remote substituents in free radical addition reactions: new evidence for the penultimate unit effect

Abstract

Ab initio molecular orbital calculations of the barrier for the addition of gamma-substituted propyl radicals to various alkenes indicate that substituents at the gamma position of a radical can significantly affect the barrier. This finding supports recent experimental evidence for an enthalpic penultimate unit effect in free-radical copolymerization. For the reactions studied in the present work, this penultimate unit effect is consistent with a significant polar contribution.