C. Barckholtz et al., A mechanistic study of the reactions of H, O ((3)p), and OH with monocyclic aromatic hydrocarbons by density functional theory, J PHYS CH A, 105(1), 2001, pp. 140-152
The chemistry of small aromatic hydrocarbons with radicals of relevance to
high temperature combustion and low temperature atmospheric processes has b
een studied computationally using the B3LYP method and transition state the
ory (TST). The reaction of H, O (P-3), and OH with aromatic hydrocarbons ca
n 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 prefer
red at 298 K, but the H-atom abstraction channel becomes dominant at high t
emperatures. The thermodynamic and kinetic preference for reactivity with a
romatic hydrocarbons increases in the order O(P-3) < H < OH. K-atom abstrac
tion from six-membered aromatic rings is more facile than from five-membere
d aromatic rings. However, radical addition to five-membered rings is therm
odynamically more favorable than addition to six-membered rings. In general
, the barrier heights and preferences for H-atom abstraction from sites wit
hin an aromatic hydrocarbon are well correlated with the corresponding C-H
band dissociation enthalpies.