Reaction mechanism and kinetic study of the •OH initiated tropospheric oxidation of 3-methyl-2-buten-1-ol: A quantum chemical investigation

In this article a theoretical study of mechanism and kinetics of the OH-initiated oxidation reaction of 3-methyl-2-buten-1-ol (MBO-321) is presented. This degradation mechanism of MBO-321 consists of H-abstraction reaction and OH-addition to olefinic bond. In addition, probable product analysis alongwith the mechanism for secondary reactions in presence of O-2 and NO has been investigated. Energetics have been studied at the CCSD(T)/6-311++g(d, p)//MP2 = full/6-31_G(d) level of theory. Thermochemical analysis has been done using CBS-QB3 method starting from the geometry obtained in the MP2 method. All the H-abstraction reactions pass through positive energy barrier except H4-abstraction channel. OH-addition to the double bond takes place via formation of the pre-reactive complex as these reaction channel pass through negative activation barrier. OH-addition is the predominant reaction pathway for the overall oxidation process. Using TST theory at 1 atm pressure and in the temperature range of 200K-400 K, the calculated rate constant and lifetime of OH-addition is k(298K)(theo) = 1.51 x 10(-10) cm(3) molecule(-1) s(-1) and 1.88 h, which is consistent with the previous experimental data, k(298K)(exp) = (1.5 +/- 0.1) x 10(-10) cm(3) molecule(-1) s(-1) and 1.9 h respectively (Imamura et al., Rate coefficients for the gas phase reactions of OH radical with methylbutenols at 298 K, Int J Chem Kinet 36: 379-385, 2004).