L. Vereecken, D. Glowacki, M. Pilling
May 27, 2015
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Chemical reviews
Abstract
ion reactions. Theoretical work correlating the CH bond strengths in hydrocarbons with their H-abstraction rate coefficient by OH radicals showed 361,362 that many terpenoids have weakly bonded H-atoms, in particular H-atoms whose abstraction leads to allylor superallyl-resonance stablized alkyl product radicals. At the same time, other H-atoms were found to be deactivated 362 towards Habstraction due to unexpected lack of stabilisation of the product radical. A particularly important example for bicyclic terpenes are the H-atoms on the bridgeheads connecting two fused ring systems where geometric constraints prevent rehybridization from an sp 3 to an sp 2 orbital arrangement in the product radical. The correlations observed between the bond strength and H-abstraction rate then led to the development of predictive correlations, dependent on the type of H-atom abstracted, that allow facile prediction of the abstraction rate, and improve the agreement between SARs and experiment for specific compounds. 362 These SARs have since been used extensively in the construction of complete degradation schemes for terpenoids, such as -pinene, 363–367 -pinene 368 or pinonaldehyde, 369 with often excellent agreement with available environmental chamber data. 5. Peroxy Radical Chemistry 5.1. Peroxy Radicals in Atmospheric Chemistry and Combustion Peroxy radicals play a central role in the oxidation of organic compounds in the troposphere. Carbon centered radicals, R , formed by H-abstraction by OH or OH addition to a double bond, react