Synchrotron Photoionization Measurements of OH-Initiated Cyclohexene Oxidation: Ring-Preserving Products in OH + Cyclohexene and Hydroxycyclohexyl + O<sub>2</sub> Reactions

Abstract

Earlier synchrotron photoionization mass spectrometry experiments suggested a prominent ring-opening channel in the OH-initiated oxidation of cyclohexene, based on comparison of product photoionization spectra with calculated spectra of possible isomers. The present work re-examines the OH + cyclohexene reaction, measuring the isomeric products of OH-initiated oxidation of partially and fully deuterated cyclohexene. In particular, the directly measured photoionization spectrum of 2-cyclohexen-1-ol differs substantially from the previously calculated Franck–Condon envelope, and the product spectrum can be fit with no contribution from ring-opening. Measurements of H<sub>2</sub>O<sub>2</sub> photolysis in the presence of C<sub>6</sub>D<sub>10</sub> establish that the addition–elimination product incorporates the hydrogen atom from the hydroxyl radical reactant and loses a hydrogen (a D atom in this case) from the ring. Investigation of OH + cyclohexene-4,4,5,5-<i>d</i><sub>4</sub> confirms this result and allows mass discrimination of different abstraction pathways. Products of 2-hydroxycyclohexyl-<i>d</i><sub>10</sub> reaction with O<sub>2</sub> are observed upon adding a large excess of O<sub>2</sub> to the OH + C<sub>6</sub>D<sub>10</sub> system

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