A computational study of the ozonolysis of sabinene

The ozonolysis of sabinene has been computationally studied at multiple levels of theory. The reaction proceeds through the so-called Criegee mechanism via the formation of a primary ozonide with two different conformations that dissociate into non-interconvertible zwitterionic Criegee intermediate (syn and anti) conformers and a carbonyl compound. The results show that the decomposition of the Criegee intermediate proceeds through different dissociation pathways. Possible pathways involve the formation of a vinyl hydroperoxide or a dioxirane ester. An alternative novel pathway that does not involve Criegee intermediate formation, but rather epoxide formation, is also investigated. The dissociation of the anti-Criegee intermediate to sabina ketone and OH radicals via the vinyl hydroperoxide pathway is more favorable than the analogous syn-Criegee intermediate dissociation. The calculations show that, between the two competing channels (the ester and vinyl hydroperoxide pathways), the ester pathway is more probable, particularly from the syn-Criegee intermediate. Furthermore, the reactions have been studied in the presence of H2O as a spectator molecule. Interestingly, it had a negligible effect on the energy barrier of the syn-ozone addition as it stabilized all the stationary points. All reactions were found to be strongly exothermic, except in the case of the dissociation of the syn-Criegee intermediate through the vinyl hydroperoxide pathway, where the reaction is endothermic.