Energy Read-out as a Probe of Kinetically Hidden Transition States

The initial energy in a reactive intermediate is derived from the transition state before the intermediate but can affect selectivity after the intermediate. In this way an observable selectivity can report on a prior, kinetically hidden mechanistic step. This new type of mechanistic probe is demonstrated here for the oxidation of 1-methylcyclobutanol by phthaloyl peroxide/Bu(4)N(+)Br(−), and it supports a hypobromite chain mechanism in place of the previously proposed hydrogen atom transfer mechanism.