Isomérisation des radicaux insaturés. III. Radicaux α,α,β-,α,β,γ- et α,α,γ-triméthallyles

α,α,β-, α,β,γ-, and α,α,γ-trimethallyl radicals have been generated in the 147.0–nm gas phase photolysis of 2,3,3-trimethyl-1-butene, 3,4-dimethyl-2-pentene, and 2,4-dimethyl-2-pentene, respectively. Under these conditions, the majority of allyl radicals have an internal energy sufficient for further decomposition: they give rise to the formation of various 1,3-dienes and small amounts of either 1,2- or 2,3-dienes. An internal sigmatropic 1,4-hydrogen atom transfer process is part of the proposed mechanism to explain such products. Moreover, the fragmentation of the trimethyl substituted allyl radicals involves the split of one β(C—C) bond, then one β(C—H), and, to a lesser extent, one central C—CH3 bond.