Cycloalkene Ozonolysis:  Collisionally Mediated Mechanistic Branching

Abstract

Master equation calculations on a computational potential energy surface reveal that collisional stabilization at atmospheric pressure becomes important in the gas-phase ozonolysis of endocyclic alkenes for a carbon number between 8 and 15. Because the reaction products from endocyclic ozonolysis are tethered, this system is ideal for consideration of collisional energy transfer, as chemical activation is confined to a single reaction product. Collisional stabilization of the Criegee intermediate precedes collisional stabilization of the primary ozonide by roughly an order of magnitude in pressure. The stabilization of the Criegee intermediate leads to a dramatic transformation in the dominant oxidation pathway from a radical-forming process at low carbon number to a secondary ozonide-forming process at high carbon number. Secondary ozonide formation is important even for syn-isomer Criegee intermediates, contrary to previous speculation. We use substituted cyclohexenes as analogues for atmospherically important mono- and sesquiterpenes, which are major precursors for secondary organic aerosol formation in the atmosphere. Combining these calculations with literature experimental data, we conclude that the transformation from chemically activated to collisionally stabilized behavior most probably occurs between the mono- and sesquiterpenes, thus causing dramatically different atmospheric behavior.

Ozonolysis of Cyclic Alkenes as Surrogates for Biogenic Terpenes: Primary Ozonide Formation and Decomposition

“…31 Both the syn and anti configuration can form a 1,2,4-trioxilane (the secondary ozonide, CYHEsoz). 11 1-Methyl-cyclohexene ozonolysis is more complicated due to its asymmetric nature. Like all alkenes, MECYHE forms a 1,2,3-trioxilane (the primary ozonide, MECYHEpoz).…”

Homogeneous and heterogeneous reactions of phenanthrene with ozone

“…The secondary organic aerosol (SOA) that results from the homogeneous reactions of VOCs effects particle pollution directly (human health, visibility, light scattering, and light absorption) and indirectly (cloud and haze formation) (Chuong et al, 2004;Kanakidou et al, 2005;Ervens and Kreidenweis, 2007). The heterogeneous reactions of surface-bound organics alter the chemical composition and hence may change the hygroscopic and toxic properties of aerosols (Rudich, 2003).…”

A computational investigation of the sulphuric acid‐catalysed 1,4‐hydrogen transfer in higher Criegee intermediates

“…A critical component of the reaction mechanism is the Criegee intermediate (CI), which retains a significant portion of the nascent energy from ozonolysis and can undergo either unimolecular decomposition or collisional stabilization with the bath gas, after which bimolecular reaction with trace atmospheric species (e.g., H 2 O, NO, NO 2 , SO 2 , organic acids, and aldehydes) becomes important. Mechanistically, CIs show considerable variation in the literature, with size and functionalization dictating branching ratios of the various excited and stabilization channels . Knowledge of these pathways is important, as the fate of CIs has an important impact on global tropospheric chemistry, directly influencing free radical and aerosol budgets …”