Use of labelled propene to distinguish between an associative, a dissociative and a concerted mechanism for the double bond shift reaction of alkenes

Abstract

The specifically labelled propene, CD₂CH—CH₃, has been used as a model alkene for investigations of catalytic double bond shift reactions. Microwave spectroscopy has been used to analyse deuteropropene mixtures produced in this reaction. It is shown how in principle the positions of the labelling D atoms after reaction can be used to deduce whether an associative, a dissociative or a concerted mechanism has operated. Specifically, the data for Ω-zeolite are consistent with an associative mechanism, presumably on Brønsted acid sites, and arguments are presented to show that this is a general mechanism for alkene double bond shift reactions on this catalyst.