Kinetics of H abstraction and addition reactions of 2,4,4-trimethyl-1-pentene by OH radical

Abstract

The rate coefficients of H abstraction and OH addition reactions of 2,4,4-trimethyl-1-pentene with OH were determined by both canonical variational transition state theory and conventional transition state theory. The potential energy surfaces were calculated at CCSD(T)/6-311++G(d, p)//BHANDHLYP/6-311(d, p) level and quantum effects were evaluated by the one-dimensional Wigner method and the multidimensional zero-curvature and small-curvature tunneling methods. 2,4,4-Trimethyl-1-pentene contains primary and secondary allylic H abstraction, alkyl, and vinylic H abstraction channels and OH addition into central and terminal carbon atoms channels. The results show that allylic H abstraction channels dominate the overall H abstractions resulting from the lower barriers, in which, primary H abstraction involves indirect channel via a reactant complex and direct channel. Moreover, OH addition reactions into central and terminal carbon atoms all contain Van der Waals reactant complexes, while the latter channel exhibits negative temperature dependence as a result of its submerged barrier. The branching ratio is more than 75% for addition reactions below 500K and more than 80% above 1100K for H abstraction reactions. Rate coefficients of all channels were fitted in terms of a quasi-Arrhenius expression.