Addition of methyl radicals to isolated, conjugated and cumulated dienes

Abstract
The rate of addition of methyl radicals to isolated, conjugated and cumulated dienes was investigated. The isolated dienes were found to behave like the corresponding mono-olefins. The conjugated dienes exhibit the expected high reactivity and the addition requires very low activation energy. The effect of methyl substituents on their reactivities was studied and the results explained quantitatively in terms of hyperconjugation and the steric ‘blocking’ effect. The effect of other substituents on their reactivities was also investigated. The reactivities of the cumulated dienes were found to be extremely low, lower than those of mono-olefins. The decrease in their reactivity seems to arise from a low A factor rather than from a high activation energy. It was shown that the addition to allene and its derivatives takes place on the central C atom and not on the terminal atoms.