Gas-Phase Kinetics of a Series of -3-Hexenyl Esters with OH Radicals under Simulated Atmospheric Conditions.

The present relative kinetic study reports on the experimentally determined gas-phase reaction rate coefficients of OH radicals with a series of seven 3-hexenyl esters. The experiments were carried out in the environmental simulation chamber made of quartz from the "Alexandru Ioan Cuza" University of Iasi (ESC-Q-UAIC), Romania, at a temperature of (298 ± 2) K and a total air pressure of (1000 ± 10) mbar. In situ long-path Fourier transform infrared (FTIR) spectroscopy was used to monitor 3-hexenyl formate (3HF, ()-CHCHCH═CH(CH)OC(O)H), 3-hexenyl acetate (3HAc, ()-CHCHCH═CH(CH)OC(O)CH), 3-hexenyl isobutyrate (3HiB, ()-CHCHCH═CH(CH)OC(O)CH(CH)), 3-hexenyl 3-methylbutanoate (3H3MeB, ()-CHCHCH═CH(CH)OC(O)CHCH(CH)), 3-hexenyl hexanoate (3HH, ()-CHCHCH═CH(CH)OC(O)(CH)CH), -3-hexenyl -3-hexenoate (3H3H, ()-CHCHCH═CH(CH)OC(O)CHCH═CHCHCH), 3-hexenyl benzoate (3HBz, ()-CHCHCH═CH(CH)OC(O)CH), and the reference compounds. The following reaction rate coefficients (in 10 cm molecule s) were obtained for the OH radical-initiated gas-phase oxidation of -3-hexenyl esters: (4.13 ± 0.45) for 3HF, (4.19 ± 0.38) for 3HAc, (4.84 ± 0.39) for 3HiB, (5.39 ± 0.61) for 3H3MeB, (7.00 ± 0.56) for 3HH, (10.58 ± 1.40) for 3H3H, and (3.41 ± 0.28) for 3HBz. The results are discussed in terms of hexenyl ester reactivity and compared with the available literature data and structure-activity relationship (SAR) estimates. The atmospheric implications based on the average lifetimes of the investigated -3-hexenyl esters are discussed in the present study. The gas-phase rate coefficients for OH radical reactions are given herein for the first time for -3-hexenyl isobutyrate, -3-hexenyl 3-methylbutanoate, -3-hexenyl hexanoate -3-hexenyl -3-hexenoate, and -3-hexenyl benzoate. The newly determined gas-phase reaction rate coefficients provide new information for existing kinetic databases and contribute to the further development of SAR methodologies useful for predicting the reactivity of oxygenated volatile organic compounds.