Theoretical Determination of Molecular Structure and Conformation. 6. The Criegee Intermediate. Evidence for a Stabilization of Its Syn Form by Alkyl Substituents

Rayleigh-Schrodinger-Mqller-Plesset (RSMP) perturbation calculations using a split-valence basis augmented by d-type polarization functions have been carried out on peroxymethylene, the so-called Criegee intermediate of the ozonolysis reaction. Accurate equilibrium structures for the bent, linear, and perpendicular molecule as well as its cyclic isomer, dioxirane, have been determined. With these structures, the barriers to rotation and inversion have been found to be 32 and 41 kcal/mol, respectively. Methyl substitution enhances these barriers. Thus, an equilibration of syn and anti alkylperoxymethylenes in solution-phase ozonolysis has to be excluded. In nonpolar solvents, the syn form of methylperoxymethylene is more stable by 3-4 kcal/mol than the anti form.