Ozonolysis of α-pinene and β-pinene: Kinetics and mechanism

A combined quantum-chemical and RRKM/ME (ME—master equation) approach is employed to investigate the structures, energetics, and kinetics of intermediate and stable species, and the yields of stabilized carbonyl oxides and OH radicals from the α-pinene and β-pinene ozonolysis reactions. The cycloaddition of O3 is highly exothermic, with the reaction energies of 55.1 and 51.1kcalmol−1 for α- and β-pinenes, respectively. Cleavage of primary ozonides yields carbonyl oxides with the barrier height of 12.2–17.5kcalmol−1. For the prompt reactions of carbonyl oxides from α- and β-pinene ozonolysis, H migration to hydroperoxides represents the dominant pathway over ring closure to dioxiranes. The kinetic calculations indicate a significant portion of stabilization for α- and β-carbonyl oxides. The yields of stabilized carbonyl oxides are estimated to be 0.34 for α-pinene and 0.22 for β-pinene. The applicability of theoretical methods for investigation of oxidation reactions of large hydrocarbon molecules is demonstrated.