Kinetics of H-abstraction from isopentanol and subsequent β-dissociation and isomerization

Abstract

Isopentanol (3-methyl-1-butanol) is a fuel additive and a second-generation biofuel; H-abstraction reactions from isopentanol by H atoms and CH3 radicals are the basic starting responses in the combustion reaction mechanism of isopentanol. This work utilizes high quantum chemical theory and kinetic methods to describe the H-abstraction reaction from isopentanol by the H atom and CH3 radical, as well as the isomerization and β-dissociation of isopentanol radicals. The potential energy surfaces (PESs) were calculated using the CCSD(T)/CBS//M06–2X-D3(0)/def2-TZVP method. The second-order Møller-Plesset perturbation theory (MP2), combined with a coupled cluster method CCSD(T), fully exploited the consistency of the Dunning basis set, the set of cc-pVQZ, cc-pVTZ, and cc-pVDZ basis sets, which were used and extrapolated to the complete basis set (CBS) limit. From the conventional transition state theory (CTST), the rate constants of the title reactions were calculated at temperatures ranging from 300 to 2000 K. Compared with the H-abstraction reaction by CH3 radicals, the H-abstraction reaction by H atoms follows the Evans-Polanyi principle. It was found that the α-site was the most favorable H-abstraction site, while the O-site was relatively difficult. In the reaction of isopentanol radicals, the isomerization reaction pathways usually dominate at low temperatures, especially the 1,4-H and 1,5-H shift isomerization reactions. β-C-C bond dissociation dominates at high temperatures. This study extends the kinetic data for the H-abstraction of isopentanol and subsequent β-dissociation and isomerization of isopentanol radicals over a wide range of pressures and temperatures.