Multichannel RRKM-TST and direct-dynamics VTST study of the reaction of hydroxyl radical with furan.

The kinetics and mechanism of the reaction of OH with furan have been theoretically studied. The potential energy surface for each possible pathway has been investigated by employing DFT, G3MP2, and CCSD methods. The potential energy surface consists of one hydrogen-bonded complex and two energized intermediates. Three different pathways are suggested to be possible for the title reaction. The most probable channel is the hydroxyl radical addition to the C(2) position on the furan ring to cause the ring-opening process. The two other pathways are hydrogen abstraction from one of the C(2) or C(3) position on furan and hydroxyl radical substitution at the C(2) or C(3) position on furan. Abstraction and substitution channels are minor paths at low temperature, but they become comparable with addition channels at high temperature. Addition and substitution reactions proceed via formation of two energized intermediates, Int(1) and Int(2). Multichannel RRKM-TST calculations have been carried out to calculate the individual and overall rate constants for addition and substitution reactions. Direct-dynamics canonical variational transition-state theory calculations with small curvature approximation for tunneling were carried out to study hydrogen abstraction pathways.