Theoretical Determination of the Rate Constant for OH Hydrogen Abstraction from Toluene

Abstract

The OH abstraction of a hydrogen atom from both the side chain and the ring of toluene has been studied in the range 275-1000 K using quantum chemistry methods. It is found that the best method of calculation is to perform geometry optimization and frequency calculations at the BHandHLYP/6-311++G(d,p) level, followed by CCSD(T) calculations of the optimized structures with the same basis set. Four different reaction paths are considered, corresponding to the side chain and three possible ring hydrogen abstractions, and the branching ratio is determined as a function of temperature. Although negligible at low temperatures, at 1000 K ring-H abstraction is found to contribute 11% to the total abstraction reaction. The calculated rate coefficients agree very well with experimental results. Side chain abstraction is shown to occur through a complex mechanism that includes the reversible formation of a collisionally stabilized reactant complex.

Reassessing the atmospheric oxidation mechanism of toluene

“…However, the detailed chemical mechanism of toluene oxidation in the atmosphere remains uncertain (4,5). Oxidation of toluene is initiated by the hydroxyl radical (OH): the initial OH−toluene reaction results in minor H abstraction (about 10%) and major OH addition (about 90%) (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). The H-abstraction pathway leads to the formation of benzaldehyde, whose oxidative pathway is well established (4,5).…”

Theoretical considerations of secondary organic aerosol formation from H-abstraction of p-xylene

“…C 7 in Fig. 2), which is a barrierless path (about 1 kcal mol À1 in activation energy from experimental measurements [40]), can occur spontaneously. For the second path starting from pre-reactive complex, the geometries of the intermediate radical and its corresponding transition structure (TS1; Fig.…”

“…In the transition [46]. e Calculated values using BHandHLYP/6-311++G ⁄⁄ method by Uc et al [40]. structure of the unimolecular decomposition of IM9, i.e.…”

Theoretical Investigation of the OH.‐Initiated Oxidation of Benzaldehyde in the Troposphere

“…This particular orientation is due to a p-type hydrogen-bond interaction that has been described elsewhere. [28] The RC-a complex differs from all the other RC structures in that the OHC radical lies in the plane of the benzaldehyde molecule. It is stabilized by two interactions: the most important one is the interaction between the H atom in the OHC radical and the O atom in benzaldehyde, while the second one involves the O atom in the OHC radical and the H atom in the aldehydic group of benzaldehyde.…”