Cyclopentadienone Oxidation Reaction Kinetics and Thermochemistry for the Alcohols, Hydroperoxides, and Vinylic, Alkoxy, and Alkylperoxy Radicals

Cyclopentadienone has one carbonyl and two olefin groups resulting in 4n + 2 pi-electrons in a cyclic five-membered ring structure. Thermochemical and kinetic parameters for the initial reactions of cyclopentadienone radicals with O-2 and the thermochemical properties for cyclopentaclienone-hydroperoxides, alcohols, and alkenyl, alkoxy, and peroxy radicals were, determined by use of computational chemistry. The CBS-QB3 composite and B3LYP density functional theory methods were used to determine the enthalpies of formation (Delta H-f degrees(298)) using the isodesmic reaction schemes with several work reactions for each species. Entropy and heat capacity, S degrees(T) and C-p degrees(T) (50 K <= T <= 5000 are determined using geometric parameters, internal rotor potentials, and frequencies from B3LYP/6-3-1G(d,p) calculations. Standard enthalpies of formation are reported for parent molecules as cydopentadienone, cyclopentadienone with alcohol, hydroperoxide substituents, and the cydopentadienone-yl vinylic, alkoxy, and peroxy radicals corresponding to loss of a hydrogen atom from the carbon and oxygen sites. Entropy and heat capacity vs temperature also are reported for the parent molecules and for radicals. The thermochemical analysis shows The R-center dot + O-2 well depths are deep, on the order of 50 kcal mol(-1) and the R-center dot + O-2 reactions to RO + O (chain branching products) for cydopentadienotie-2-yl and cydopentadienone-3-yl have unusually low reaction (Delta H-rxn) enthalpies, some 20 or so kcal/inol below the entrance channels. Chemical activation kinetics using quantum RRK analysis for k(E) and master equation for falloff are used to, show that significant chain branching as a function of temperature and pressure can occur when these vinylic radicals are formed.