OH Yields in the Gas-Phase Reactions of Ozone with Alkenes

Hydroxyl radical yields are reported for the gas-phase ozonolyses of a range of alkenes. 1,3,5-Trimethylbenzene was employed as an OH tracer, and the diminution in its concentration was used to calculate OH yields by both a simple analytical kinetic expression and a numerically integrated model. The following OH yields were obtained, relative to alkene consumed:  ethene (0.14), propene (0.32), 2-methylpropene (0.60), 2,3-dimethyl-2-butene (0.89), isoprene (0.44), β-pinene (0.24), and α-pinene (0.83). A structure activity relationship (SAR) is presented for the estimation of OH yields based on structural moieties and reaction branching ratios. Reaction stoichiometries (Δ[alkene]/Δ[ozone]) are also reported, along with primary carbonyl yields measured in the presence and absence of excess SO2, both under “OH-free” conditions. Reaction stoichiometries are shown to be correlated with alkene OH yields, and the mechanistic implications of this observation are discussed. The fractional increase in primary carbon...