Within this dissertation, we report on explorations of reactive oxygen species with implications for combustion and atmospheric chemistry. Various computational approaches, including density functional theory (DFT) and master equation methods, were used to complete these projects.; The majority of this thesis involves the oxidation pathways of the alkylated heterocycles that provide a model framework for understanding coal combustion. The enthalpies and energies of reaction for hydrogen-atom loss and alkyl-group fragmentations at various temperatures were calculated via density functional theory (B3LYP/6-311+G**//B3LYP/6-31G*); these results were calibrated against CBS-QB3 calculations. It was suggested that both hydrogen-atom loss and alkyl-group loss reactions will contribute as initiation steps for the high-temperature combustion reactions of these rings. Longer alkyl chains will increase reactivity, and the azabenzene units are more likely to react than the five-membered heterocyclic rings. The initial steps of radical formation are expected to become more favorable at high temperatures.; The oxidation steps of these radicals were shown to be exothermic and exoergic, as expected. DFT studies (B3LYP/6-311+G**//B3LYP/6-31G*) showed that these resultant peroxy radicals were more likely to undergo intramolecular reactions to form bicyclic structures. Furthermore, several pathways seemed feasible and must be considered in rationalizing coal chemistry: formation of either a four-membered or five-membered ring occurs with similar kinetics and thermodynamics; cyclization at nitrogen to form a nitroso species has a high reaction barrier but is ultimately quite exoergic. An internal H-atom transfer can occur on the substituted side chain with a low barrier and favorable energy of reaction.; We have completed other projects with implications for combustion chemistry and oxygenated species. 1,5-H transfers proceed readily for n-propylperoxy radical due to this radical's ability to adopt a six-membered transition state. This reaction and others available to this species are of interest due to the ability of n-propylperoxy radical to serve as a model compound for understanding the combustion of larger hydrocarbon fuels. Conformational possibilities for this species were explored via B3LYP/6-31G* and mPW1K/6-31+G** levels of theory to ensure that rotational barriers would not compete with energies of reaction. It was seen that rotamer interconversion occurs with barrier heights of less than 5 kcal/mol, far less than the relevant reaction activation barriers (∼20-25 kcal/mol); thus, rotamer interconversion was not expected to affect overall energetics. Building on these results, the unimolecular decomposition of propan-1-ol-1-peroxy radical was similarly modeled using DFT methods. It was seen than the quantitative energetics of the relevant decompositions were very similar to those of the hydrocarbon analogue, although a wider variety of functionalized products were formed.; Complexes of ethanol with various solvents were modeled to better understand certain spectroscopic phenomena and potential atmospheric behaviors of oxygenated species. Experimental work on these complexes had noted a red shift due to complexation of ethanol with benzene that was not seen with any other solvents. Theoretical spectra were generated using HF/6-31G* and MP2/6-31G* optimizations and compared well to the experimental spectra. The red shift seen in benzene was attributed to an interaction of ethanol with the pi system of the benzene ring.; Finally, engine performance varies given the fuel of interest. Hydrogen has often been proposed as an alternative fuel that would improve engine performance and minimize harmful emissions. Its use as a fuel additive was explored with n-heptane and the primary reference fuels (a mixture of iso-octane and n-heptane), using the master equation program CHEMKIN 4.1. It was seen that hydrogen augmentation did increase flame
展开▼
