Abstract: Effects of Intramolecular and Intermolecular Interactions on Oxidations by Dimethyldioxirane. The Density Functional Theory B3LYP/6-31G* method is used to provide a detailed understanding of the origins of intra- and intermolecular (solvent) effects on the epoxidation of C-C double bonds and oxidation of primary amines by dimethyldioxirane (DMDO). We find that the presence of hydrogen bond donors, either internal in the form of substituents on the substrate or external in the form of hydrogen bonding solvents, leads to dramatically decreased activation barriers for epoxidation of the C=C bond as well as for oxidation of amines. Solvent polarity, studied using the SCIPCM model, also lowers the activation barrier although this effect is substantially smaller than seen with hydrogen bonding interactions. The effect of solvent polarity is larger in the oxidation of primary amine than in the epoxidation reaction due to very polar transition state structure seen in the oxidation of amine.