title: Thermochemistry and kinetics of hydrogen abstraction by methyl radical from polycyclic aromatic hydrocarbons.
abstract: Thermodynamic and kinetic properties relating to hydrogen abstraction by methyl radical from various sites in polycyclic aromatic hydrocarbons (PAHs) have been investigated. The reaction enthalpies (298 K), barriers (0 K), and activation energies and pre-exponential factors (700-1100 K), have been calculated by means of density functional theory, specifically with B3-LYP/6-311G(d,p) geometries, followed by BMK/6-311+G(3df,2p) single-point energy calculations. For uncongested sites in the PAHs, a reasonable correlation is obtained between reactivities (as characterized by the reaction barriers) and reaction enthalpies. This is reflected in a Bell-Evans-Polanyi (BEP) relationship. However, for congested sites, abstraction is accompanied both by lower reaction enthalpies (due to relief of steric strain) and also by reduced reactivities (due to significantly increased steric hindrance effects in the transition structures), so that the BEP relationship does not hold. In addition, the reaction enthalpies and kinetic parameters for the series of linear acenes indicate that abstraction is more difficult from the central rings.
authors.affiliation: Center for Molecular Modeling, Proeftuinstraat 86, and Laboratorium voor Petrochemische Techniek, Krijgslaan 281-S5, Ghent University, B-9000 Ghent, Belgium. karen.hemelsoet@UGent.be
authors.forename: Karen
authors.initials: K
authors.lastname: Hemelsoet
authors.forename: Veronique
authors.initials: V
authors.lastname: Van Speybroeck
authors.forename: Damian
authors.initials: D
authors.lastname: Moran
authors.forename: Guy B
authors.initials: GB
authors.lastname: Marin
authors.forename: Leo
authors.initials: L
authors.lastname: Radom
authors.forename: Michel
authors.initials: M
authors.lastname: Waroquier