A Mechanistic Study of the Reactions of H, O (³P), and OH with Monocyclic Aromatic Hydrocarbons by Density Functional Theory

Abstract

The chemistry of small aromatic hydrocarbons with radicals of relevance to high temperature combustion and low temperature atmospheric processes has been studied computationally using the B3LYP method and transition state theory (TST). The reaction of H, O (3P), and OH with aromatic hydrocarbons can proceed by two mechanisms: hydrogen-atom abstraction or radical addition to the ring. The calculated free energies for the transition state barriers and the overall reactions show that the radical addition channel is preferred at 298 K, but the H-atom abstraction channel becomes dominant at high temperatures. The thermodynamic and kinetic preference for reactivity with aromatic hydrocarbons increases in the order O(3P) < H < OH. H-atom abstraction from six-membered aromatic rings is more facile than from five-membered aromatic rings. However, radical addition to five-membered rings is thermodynamically more favorable than addition to six-membered rings. In general, the barrier heights and preferences for H-atom abstraction from sites within an aromatic hydrocarbon are well correlated with the corresponding C−H bond dissociation enthalpies.

Two theoretical simulations of hydrocarbons thermal cracking: Reactive force field and density functional calculations

“…6 displays the rate constant of these two elementary processes calculated at the BH&HLYP/ 6-31G(d,p) and B3LYP/6-31G(d,p) level of theory, respectively. Rate constant of both reactions were found to be equivalent at 1030 K. This temperature is in the range of that estimated with the cook-off simulation and close to that found for toluene system [35,36]. Thus, at 3800 K, the hydrogen abstraction reaction forming H 2 is highly favored over the addition reaction.…”

Hydroxyl Radical Adducts to Pyridine. The Generation and Properties of the Elusive N-Hydroxypyridyl Radical

“…39 That result was likely to be an artifact of B3LYP calculations that were reported to underestimate activation energies in radical additions to several unsaturated systems. 40 Hydrogen Atom Addition to Pyridine-N-oxide.…”

Computational investigation of the adsorption and photocleavage of chlorobenzene on anatase TiO2 surfaces

“…Barckholtz et al [57] have concluded, in their study of monocyclic aromatic hydrocarbon reaction with Table 2 Bond order changes followed S 0 ? S 1 excitation for the adsorption model seen in Fig.…”