Oxygen centered radicals serve as important atmospheric cleansing agents with hydroxyl radical serving as a day-time “detergent” and nitrate radical operating throughout the night. To understand these radicals fully, it is important to study these compounds both in the gas-phase, and in solution to simulate their effects in the atmosphere, on and within water droplets, and on aerosols surfaces. Previous work on the hydroxyl radical has shown that solvent polarity and hydrogen bonding stabilize the transition state and accelerate the rate of hydrogen abstraction in solution. Based on preliminary calculations we proposed that a similar effect might occur for the nitrate radical, because it is such a strong oxidant both in the gas-phase and in solution. Rate constants for hydrogen abstraction reactions from hydrocarbons, alcohols, and ethers by the NO<sub>3</sub> radical in acetonitrile and water were determined by laser flash photolysis. These results were also compared to gas-phase experiments. Despite calculations predicting a polar transition state that should facilitate hydrogen bonding in the gas-phase, experimental evidence shows that rate constants in water were slightly lower than in CH<sub>3</sub>CN. Further, the solution-phase reactions exhibit rate enhancement with respect to their gas-phase counterparts, consistent with the notion of a polarized transition state that can be stabilized in a polar solvent. We are doing calculations to full understand the role (if any) of hydrogen bonding in both the ground and transition states.

Role of solvent polarity and hydrogen bonding on nitrate radical reactivity

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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