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. alpha -phellandrene and alph a -terpinene, also undergo fast H-abstraction. In this work, quantum chemic al CH bond strengths were calculated for selected (poly)alkenes yielding re sonance-stabilised product radicals. Available H-abstraction rate data were found to show a manifest anticorrelation with these bond strengths. Nevert heless, it is also concluded that abstraction rates cannot be related uniqu ely to the C-H bond strengths. The bond strengths listed can provide guidan ce in constructing atmospheric degradation mechanisms; a semiquantitative d iscussion is given. (C) 2001 Elsevier Science B.V. All rights reserved.