Department of Chemistry, Macalester College, Saint Paul, Minnesota 55105-1899, USA.
J Phys Chem A. 2010 Sep 2;114(34):9192-204. doi: 10.1021/jp105358v.
Alkene ozonolysis is a major source of hydroxyl radical (*OH), the most important oxidant in the troposphere. Previous experimental and computational work suggests that for many alkenes the measured *OH yields should be attributed to the combined impact of both chemically activated and thermalized syn-alkyl Criegee intermediates (CIs), even though the thermalized CI should be susceptible to trapping by molecules such as water. We have used RRKM/master equation and variational transition state theory calculations to quantify the competition between unimolecular isomerization and bimolecular hydration reactions for the syn and anti acetaldehyde oxide formed in trans-2-butene ozonolysis and for the CIs formed in isoprene ozonolysis possessing syn-methyl groups. Statistical rate theory calculations were based on quantum chemical data provided by the B3LYP, QCISD, and multicoefficient G3 methods, and thermal rate constants were corrected for tunneling effects using the Eckart method. At tropospheric temperatures and pressures, all thermalized CIs with syn-methyl groups are predicted to undergo 1,4-hydrogen shifts from 2 to 8 orders of magnitude faster than they react with water monomer at its saturation number density. For thermalized anti acetaldehyde oxide, the rates of dioxirane formation and hydration should be comparable.
烯烃臭氧化是羟基自由基 (*OH) 的主要来源，*OH 是对流层中最重要的氧化剂。先前的实验和计算工作表明，对于许多烯烃，测量的 *OH 产率应该归因于化学激活和热化的顺式烷基 Criegee 中间体 (CI) 的综合影响，尽管热化的 CI 应该容易被水等分子捕获。我们使用 RRKM/主方程和变分过渡态理论计算来量化顺式和反式 2-丁烯臭氧化形成的乙醛氧化物和具有顺式甲基的异戊二烯臭氧化形成的 CI 中，分子内异构化和双分子水合反应之间的竞争。统计速率理论计算基于 B3LYP、QCISD 和多系数 G3 方法提供的量子化学数据，并用 Eckart 方法校正了热速率常数的隧道效应。在对流层温度和压力下，所有具有顺式甲基的热化 CI 预计将经历 1,4-氢位移，速度比它们在饱和数密度下与水单体反应快 2 到 8 个数量级。对于热化的反乙醛氧化物，环氧化合物的形成和水合速率应该相当。
