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Various reactions with implications for combustion chemistry were modeled. The enthalpies and energies of reaction for hydrogen-atom loss and alkyl-group fragmentations at various temperatures were calculated for the alkylated heterocycles that provide a model framework for understanding coal combustion, using density functional theory (B3LYP/6-311+G**//B3LYP/6-31G*) and CBS-QB3 calculations. The oxidation steps of the resulting radicals were modeled, and pathways of the resulting peroxy radicals explored. These species can undergo intramolecular reactions to form bicyclic structures. Several pathways are 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. Conformational possibilities for n-propylperoxy radical 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. Building on these results, the unimolecular decomposition of propan-1-ol-1-peroxy radical was similarly modeled using DFT methods. The quantitative energetics of the relevant decompositions were similar to those of the hydrocarbon analogue, although a wider variety of functionalized products were formed; these small model compounds are of interest in understanding larger hydrocarbon and functionalized fuels. 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. 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.