Kinetic study of the cyclohexadienyl radical. Part 2.—Patterns of combination and disproportionation with the methyl, ethyl, sec-propyl and tert-butyl radicals

The pattern of interaction of the cyclohexadienyl radical with each of a series of primary, secondary and tertiary alkyl radicals R· is given by the percentages of the products: [graphic omitted] The almost constant ratio of the products of combination implies that this pattern is determined almost exclusively by the properties of the cyclohexadienyl radical, and we have proposed that combination at the para position is favoured because the spin density is highest there. Conversely, the monotonic increase of the percentage of disproportionation with the degree of substitution at the α carbon atom of the alkyl radical parallels the behaviour of the alkyl radicals in mutual interaction. The significance of these results is discussed in relation to current models of the transition state.