H-atom abstraction by OH-radicals from (biogenic) (poly)alkenes: C–H bond strengths and abstraction rates

Although most (poly)alkenes+OH reactions proceed nearly exclusively by OH-addition, specific biogenic polyalkenes, e.g. α-phellandrene and α-terpinene, also undergo fast H-abstraction. In this work, quantum chemical C–H bond strengths were calculated for selected (poly)alkenes yielding resonance-stabilised product radicals. Available H-abstraction rate data were found to show a manifest anticorrelation with these bond strengths. Nevertheless, it is also concluded that abstraction rates cannot be related uniquely to the C–H bond strengths. The bond strengths listed can provide guidance in constructing atmospheric degradation mechanisms; a semiquantitative discussion is given.