| The focus of this dissertation is to improve our understanding of chemical reactions which are important in both combustion and atmospheric environments. The following paragraphs describe the studies carried out and reported in this dissertation. Density functional theory was utilized to determine whether the addition of O2(3Sigmag) to 2-oxepinoxy radical, a proposed intermediate in the unimolecular decomposition of phenylperoxy radical, followed by unimolecular rearrangement and decomposition results in the formation of experimentally detected C1-C5 products via oxidative combustion of benzene. Pathways resulting from the initial formation of 1,2-dioxetanyl, 1,3-peroxy, 1,4-peroxy, hydroperoxy, and peroxy moiety scission intermediates were calculated. At temperatures between 500-750 K, the formation of peroxyoxepinone radicals and their decomposition pathways and products are competitive with those proposed by Fadden for the unimolecular decomposition of 2-oxepinoxy radical.; The conformational distribution and unimolecular decomposition pathways for n-propylperoxy radical have been generated at the CBS-QB3, B3LYP/6-31+G** and mPWIK/6-31+G** levels of theory. At the CBS-QB3 level, the 298 K distribution of rotamers is predicted to be 28.1, 26.4, 19.6, 14.0, and 11.9% for the gG, tG, gT, gG', and tT conformations, respectively. The detailed CBS-QB3 potential energy surface for the unimolecular decomposition of n-propylperoxy radical indicates that important bimolecular products could be derived from two 1,4-H transfer mechanisms available at T < 500K, primarily via an activated n-propylperoxy adduct.; Substituent effects on the bond dissociation enthalpies (BDEs) and hydroxyl radical addition reactions for a series of mono-substituted ethenes and benzenes have been studied using density functional theory (DFT). In each case, a hydrogen atom on the ethene and benzene has been replaced by the following series of substituents: F, Cl, CF3, CH3, CN, CHO, OCH3, OH, NH2, NO2, SCH3, and SH. BDEs for the cis ethene and ortho benzene C--H bonds are shown to correlate well with the atoms in molecule (AIM) derived charge localized on the substituent of the parent molecule when steric interactions are minimized. When the ethene beta-addition and benzene ortho and para addition barrier heights are compared with the adiabatic ionization energies, a good correlation is obtained.; The C--H bond dissociation energies and H-atom abstraction and radical addition reactions of hydrogen atom and hydroxyl radical with naphthalene, anthracene, phenanthrene, 4H-cyclopenta[d e,f]phenanthrene, benzo[c]phenanthrene, benzo[g,h,i]fluoranthene, and corannulene have been studied using density functional theory. Thermodynamically, hydrogen atom and hydroxyl radical addition reactions with PAHs are more favorable than H-atom abstraction reactions. The bond dissociation energies for the PAHs studied here are typical for aromatic C--H bonds (∼111 kcal/mol). (Abstract shortened by UMI.)... |
