Arrhenius parameters for the addition of HO 2 radicals to pent-1-ene, hex-1-ene, and cis- and trans-hex-2-ene over the range 400–520 °C

Studies have been made of the addition of HO2 radicals to four C5 and C6 alkenes, each alkene being co-oxidised with propene in an aged boric-acid-coated vessel over the temperature range 400–520 °C. From measurements of the relative yields of the oxiranes produced in each co-oxidation, Arrhenius parameters have been obtained for the addition of HO2 radicals to pent-1-ene, hex-1-ene, and cis- and trans-hex-2-ene by use of reaction (5) as the reference reaction with A5= 109.11 ± 0.30 dm3 mol–1 s–1 and E5= 62.3 ± 5 kJ mol–1: [graphic omitted] These results confirm earlier results that the addition of an HO2 radical to an alkene has a high activation energy. However, the value of the activation energy is very structure dependent, as shown by the excellent correlation between the activation energy and the ionisation energy of the alkene, the latter quantity being a measure of the availability of the π electrons in the double bond.Arrhenius parameters for the reverse decomposition of the HO2 adducts have been calculated thermochemically. It is suggested that this process is too slow to compete with the alternative decomposition to given an oxirane and OH.