Dioxetanones' peroxide bond as a charge-shifted bond: implications in the chemiluminescence process

Six dioxetanone molecules, ranging in complexity from simple dioxetanone to firefly dioxetanone, were studied by performing M06/6-311G(d,p) calculations. The quantum theory of atoms in molecules and the electron localization function was applied to analyze the peroxide and carbon-carbon bonds of the dioxetanone ring. Both approaches demonstrated that the peroxide bond is not covalent, but charge-shifted. This means that for this bond the covalent electron sharing is relatively unimportant, and it is the stabilizing resonance energy that causes the bonding. For the contrary, the carbon-carbon bond is covalent. These discoveries indicate that no biradical species should be formed in the dioxetanone decomposition, and that the most probable rate-determining step should be the carbon-carbon cleavage.