The preparation and the isomerisation of some 1,12-diphenyldodec-6-enes are described. The migration of the double bond in the presence of triethylborane gives an equilibrium between all the positional isomers. The isomer with the double bond conjugated with the aromatic nucleus is preferred but substantial quantities of the other isomers are also present at equilibrium. The concentration of the “conjugated isomer” is very sensitive to steric hindrance but seems to be independent of the inductive effect of substituents on the aromatic rings.