Singlet oxygen is one of important reactive oxygen species that determines the fate of organic compounds in natural aquatic environmental under sunlit irradiation. Chromophoric dissolved organic matter photosensitizes ground state molecular oxygen dissolved in water to generate the first electronically excited state, singlet oxygen. While the initial rate-determining charge transfer reaction mechanisms and kinetics of singlet oxygen have been extensively studied and documented for phenolates and phenols in the literature, no comprehensive studies have performed to elucidate the reaction mechanisms with organic compounds that have various functional groups because of the difficulties in quantifying the resultant intermediates and products. The goal of this study is to elucidate the reaction mechanism of singlet oxygen with organic compounds in the aqueous phase.<br/>We used Densify Functional Theory calculations to investigate each step of elementary reactions from reactants, the formation of a precursor-complex, transition states, and products for 100 structurally diverse organic compounds. The analysis of kinetics and the formation of a precursor-complex confirms the initial charge separation step. The calculations of aqueous-phase free energies of activation and reactions determine the kinetics and thermodynamic properties of single electron transfer and addition reactions. By comparing to the experimentally measured literature-reported rate constants, we determined linear free energy relationships for each reaction mechanism and elucidated the dominant reaction mechanism. The analysis also highlights the role of functional groups on overall reactivity of singlet oxygen with organic compounds. This study advances our understanding and predicting the photochemical fate of organic compounds in natural aquatic environment.

Mechanistic insight into the reactivities of aqueous-phase singlet oxygen with organic compounds

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.