“ene-type 1” and “ene-type 2”. Type 1, in which the migrating hydrogen atom is abstracted from 1, is ubiquitous (except with 2-methoxypropene) but is always a minor reaction; type 2, in which the migrating hydrogen atom is transferred to 1, was encountered only in the cases of 3-methylenecyclohexene, in which it is a major reaction path, and isoprene. Both types were found to be slightly concerted. In this