Theoretical studies on thermal stability of alkyl-substituted 1,2-dioxetanes

The geometry of thirty alkyl-substituted 1,2-dioxetanes derivatives was optimized using theoretical methods. It was found that AM1 and PM3 semiempirical methods do not adequately predict dihedral angles of the peroxidic ring of highly stabilized 1,2-dioxetanes. Geometric parameters calculated by ab initio and hybrid DFT methods are in better agreement with experimental activation parameter data than the one obtained by semiempirical calculations. Among those, the B3LYP method with the 6-31G(d) basis set is the most adequate one. Very good correlation between theoretical carbon-carbon bond distances and experimental activation parameters was found for all ab initio and hybrid DFT methods, whereas, oxygen-oxygen bond distances and dihedral angles do not correlate well with the activation parameters. Results obtained by different methods are compared and a qualitative explanation for the stabilization effect of alkyl groups on the 1,2-dioxetane ring is proposed.