Kinetics of the Hydrogen Abstraction Reaction from 2-Butanol by OH Radical

The kinetics of the hydrogen abstraction from 2-butanol by hydroxyl radical have been studied using multipath variational transition-state theory with the multidimensional small curvature tunneling approximation. The rate constants for each of the five hydrogen abstraction sites (C1, C2, C3, C4, and O) and the overall reaction have been computed by direct dynamics based on M08-HX/6-311+G(2df,2p) electronic structure calculations. We show that multistructural torsional anharmonicity, anharmonicity differences of high-frequency modes between the transition structures and the reactants, and reaction-path dependence of multiple reaction paths are all important factors for determining accurate reaction rates and branching fractions for this problem. The reaction barrier heights for abstraction from various sites follow the order C2 < C3 < C4 < C1 < O, but the reactivities of the various sites do not precisely follow the inverse order of barrier heights, and the order of reactivities depends on temperature. The abstractions from C2 and C3 have the largest contribution to the total reaction rate from 200 to 2000 K.