Direct observation of the equilibrium between cyclohexenyl radicals, O2, and cyclohexenylperoxy radicals Original Research Article

Reaction of cyclohexenyl radicals with O2 has been studied by a combination of pulsed laser photolysis and photoionization mass spectrometry. These radicals could be generated either by photolyzing 3-bromocyclohexene or by the two step reaction of carbon tetrachloride photolysis followed by the H atom abstraction reaction of Cl atom with cyclohexene. The equilibrium between cyclohexenyl radicals, O2 and cyclohexenylperoxy radicals could be observed at a temperature of 361 K. An analysis of the temporal signal of cyclohexenyl radicals was used to evaluate both the forward and reverse rate constants as well as the equilibrium constant. Use of the latter together with an estimated ΔS0 for the reaction yields a C–O bond energy of 80.4±4.2 kJ mol−1 in the RO2 adduct.