Experiments are described intended to test a mechanism for copper-catalyzed perester decompositions similar to that proposed by Kochi. Major steps are reduction of perester by CUI to yield l-butoxy radicals, attack of t-butoxy radicals on hydrocarbon substrates, and oxidation of the resulting hydrocarbon radicals by Cu" to carbonium ions. Relative reactivities of seven hydrocarbons are shown to be the same in t-butyl peracetate and ...