Reactivity of allylic hydrogen in cyclohexadiene towards OH radicals

The yield of benzene in the reaction of 1,4- and 1,3-cyclohexadiene with OH radicals in the presence of oxygen was determined using H₂O₂ and CH₃ONO as OH radical sources. Both in the H₂O₂ and the CH₃ONO systems, the yield of benzene from 1,4-cyclohexadiene was 15.3% and the yield from 1,3-cyclohexadiene was 8.9%. On the basis of the obtained yields, the rate constant for allylic hydrogen abstraction per C? H in cyclohexadiene was determined to be 3.8 × 10^?12 cm³ molecule^?1 s^?1. The branching ratio of the hydrogen abstraction to overall reaction for 1-butene and 1-pentene was estimated to be (25–14)% by applying the obtained rate constants. The result was in good agreement with the branching ratio determined directly by use of the discharge flow photoionization mass spectrometer by Biermann, Harris, and Pitts 4].