Theoretical Study of Epoxidation Reactions Relevant to Hydrocarbon Oxidation

Advances in computational modeling tools have allowed for the construction of detailed chemical models of oxidation processes to enhance the understanding of mechanisms and answer questions of interest in diverse fields such as DNA damage, lubricant oxidation, food chemistry, and art conservation. The construction of detailed kinetic models is facilitated by the use of kinetic correlations, such as Evans-Polanyi relationships, where the activation energy, E_A, is related linearly to the heat of reaction, ΔH_R: E_A = E₀ + α ΔH_R. In this work, we present an Evans-Polanyi relationship based on properties determined from hybrid G4 quantum chemical calculations for an epoxidation reaction of peroxy species. We explore a broader chemical space at a higher level of theory than previous reports, and as a result, the importance of several key structural features, such as alkylhydroperoxy functional groups, that can strongly influence the trends observed was revealed. We suggest a subdivision of the reaction family into separate Evans-Polanyi relationships to accurately capture E_A values quantitatively. We also quantified the impact of local unsaturation during the epoxidation reaction, demonstrating that it raises the energy barrier by 6.6 kcal/mol on average when compared to that of an alkyl radical counterpart. (Graph Presented).