Gas-Phase Kinetics of a Series of cis-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 cis-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 cis-3-hexenyl formate (Z3HF, (Z)–CH₃CH₂CHCH(CH₂)₂OC(O)H), cis-3-hexenyl acetate (Z3HAc, (Z)–CH₃CH₂CHCH(CH₂)₂OC(O)CH₃), cis-3-hexenyl isobutyrate (Z3HiB, (Z)–CH₃CH₂CHCH(CH₂)₂OC(O)CH(CH₃)₂), cis-3-hexenyl 3-methylbutanoate (Z3H3MeB, (Z)–CH₃CH₂CHCH(CH₂)₂OC(O)CH₂CH(CH₃)₂), cis-3-hexenyl hexanoate (Z3HH, (Z)–CH₃CH₂CHCH(CH₂)₂OC(O)(CH₂)₄CH₃), cis-3-hexenyl cis-3-hexenoate (Z3HZ3H, (Z,Z)–CH₃CH₂CHCH(CH₂)₂OC(O)CH₂CHCHCH₂CH₃), cis-3-hexenyl benzoate (Z3HBz, (Z)–CH₃CH₂CHCH(CH₂)₂OC(O)C₆H₅), and the reference compounds. The following reaction rate coefficients (in 10^–11 cm³ molecule^–1 s^–1) were obtained for the OH radical-initiated gas-phase oxidation of cis-3-hexenyl esters: (4.13 ± 0.45) for Z3HF, (4.19 ± 0.38) for Z3HAc, (4.84 ± 0.39) for Z3HiB, (5.39 ± 0.61) for Z3H3MeB, (7.00 ± 0.56) for Z3HH, (10.58 ± 1.40) for Z3HZ3H, and (3.41 ± 0.28) for Z3HBz. 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 cis-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 cis-3-hexenyl isobutyrate, cis-3-hexenyl 3-methylbutanoate, cis-3-hexenyl hexanoate cis-3-hexenyl cis-3-hexenoate, and cis-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.