Dioxetane Chemiluminescence. The Effect of Deuterium Substitution on the Thermal Decomposition of trans-3,4-Diphenyl-1,2-dioxetane.

Trans-Diphenyl-1,2-dioxetane was prepared by cyclization of the corresponding beta-bromohydroperoxide. Thermal decomposition of this compound proceeds with an activation energy of 23 or - 1.6 kcalmol to yield benzaldehyde 10 or - 2 of which was in an excited triplet state. The effects of replacement of a dioxetane ring proton with a deuterium were investigated. No detectable partitioning between electronically excited protio and deutero benzaldehyde was detected. The secondary deuterium isotope effect on the rate of thermal decomposition of this dioxetane was found to be 1.01 or - .02. That the absence of an isotope effect is consistent only with a stepwise decomposition for 1,2-dioxetanes is suggested. Author