Abstract: The vapor-phase thermolyses of 3-hydroxy-l, 5-hexadienes result in rearrangement to A5-unsaturated carbonyl compounds and in the formation of cleavage products. Based on a series of ten methyl-substituted compounds studied, the formation of these products is interpreted on the basis of two competing concerted bond reorganizations both of which proceed through a cyclic six-membered transition state. Production of cleavage products ...