15min:

WAI-TO CHAN AND IAN P. HAMILTON, Department of Chemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada N2L 3C5.

Ozonolysis of alkenes is initiated by the cycloaddition of ozone to the double bond to form a primary ozonide (POZ). Decomposition of the vibrationally excited POZ is a major source of various organic pollutants. The dominant mechanistic pathway is generally believed to be a concerted cleavage of the C=C and the O--O bonds to form a Criegee intermediate (CI) and an aldehyde followed by unimolecular decompostion of the vibrationally excited CI. We report ab initio calculations of the ethene and propene POZ using DFT-BH&HLYP, CCSD(T) and QCISD(T) methods. Our results suggest the favoured pathway to be the non-concerted cleavage of the POZ to a diradical oxy-peroxy intermediate forming CI and aldehyde. Competitive channels for formation of OH, HO₂ and epoxides are also studied. The possibility of verification of the mechanism of POZ fragmentation via spectroscopic detection of prompt formation of OH and HO₂ is discussed.