Structure−Reactivity Relationship in Ketones + OH Reactions:  A Quantum Mechanical and TST Approach

Abstract

CCSD(T)//BHandHLYP/6-311G(d,p) calculations have been performed to study the OH hydrogen abstraction reaction from three characteristic ketones. A previously proposed complex mechanism, involving the formation of a stable prereactive complex, is confirmed for some channels. The temperature dependence of the rate coefficients ( k ) is studied for all significant reaction channels over the temperature range 290−500 K, using conventional transition state theory. A good agreement between calculated and experimental k at 298 K has been obtained. The rate coefficient for the formation of the beta radical in 2-pentanone is found to be significantly larger than those of the competing channels. The explanation for this behavior, previously attributed only to the structure of the reactant complex, was found to be also a consequence of the lowering of the reaction barrier due to the presence of a hydrogen-bond-like interaction in the transition state.