Computational investigation on mechanisms and kinetics of gas-phase reactions of 4-hydroxy-2-pentanone (4H2P) with hydroxyl radicals and subsequent reactions of CH3C(O)CH2C·(OH)CH3 radical.

The mechanistic, thermochemical, and kinetic study of the 4-hydroxy-2-pentanone (4H2P) + OH radical reaction is performed for the first time by employing quantum theoretical calculations. The potential energy diagram was evaluated for five possible reaction pathways at the CCSD(T)/cc-pVTZ//BH&HLYP/cc-pVTZ level of theory. Theoretical rate coefficients of five abstraction pathways are computed as a function of temperature (210–350 K) utilizing the canonical variational transition state theory (CVT) with small-curvature tunneling (SCT). A three-parameter modified Arrhenius equation is used to fit rate coefficients. The thermodynamic quantities like reaction enthalpy and Gibbs free energy are calculated at the BH&HLYP/cc-pVTZ level of theory. According to thermodynamic analysis, the hydrogen abstraction from the –CH group adjacent to the hydroxyl group occurs more favorably and is the dominant pathway with minimum barrier height. The structure–activity relationship is explored by comparing rate coefficients of the titled reaction with the literature values of similar species. The subsequent fate of the alkyl radical (CH3C(O)CH2C·(OH)CH3) is further studied in a NO-rich environment resulting in the formation of acetone, NO2, and oxygen as the major final products. [ABSTRACT FROM AUTHOR]