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Double Bonds Are Key to Fast Unimolecular Reactivity in First-Generation Monoterpene Hydroxy Peroxy Radicals
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2020-04-01 , DOI: 10.1021/acs.jpca.0c01079
Kristian H. Møller 1 , Rasmus V. Otkjær 1 , Jing Chen 1 , Henrik G. Kjaergaard 1
Affiliation  

Monoterpenes are a group of volatile organic compounds (VOCs) emitted to the atmosphere in large amounts. Studies have linked the autoxidation of monoterpenes to the formation of secondary organic aerosols, which impact Earth’s climate and human health. Here, we study the hydroxy peroxy radicals formed by OH- and O2-addition to the six atmospherically relevant monoterpenes α-pinene, β-pinene, Δ3-carene, camphene, limonene, and terpinolene. The six monoterpenes all have a six-membered ring but differ in the binding pattern of the four remaining carbon atoms and the position of the double bond(s). We use a multiconformer transition state theory approach to calculate the rate coefficients of the peroxy radical hydrogen-shift (H-shift) and endoperoxide formation reactions of these peroxy radicals. Our results suggest that primarily the isomers with a carbon–carbon double bond remaining after OH- and O2-addition undergo unimolecular reactions with rate coefficients large enough to be of atmospheric importance. This greatly limits the number of potentially important unimolecular pathways. Specifically, we find that the ring-opened α- and β-pinene isomers as well as isomers of limonene and terpinolene have unimolecular reactions that are fast enough to likely dominate their reactivity under most atmospheric conditions.

中文翻译:

双键是第一代单萜羟基过氧自由基中快速单分子反应性的关键

单萜是大量排放到大气中的挥发性有机化合物(VOC)。研究已经将单萜的自氧化作用与次生有机气溶胶的形成联系起来,这影响了地球的气候和人类健康。在这里,我们研究由OH-和O形成的羟基过氧化自由基2 -addition于六个大气相关单萜α蒎烯,β蒎烯,Δ 3-胡萝卜素,hen烯,柠檬烯和萜品油烯。六个单萜均具有一个六元环,但是在其余四个碳原子的结合方式和一个或多个双键的位置方面不同。我们使用多聚体过渡态理论方法来计算过氧自由基氢转移(H转移)和这些过氧自由基的内过氧化物形成反应的速率系数。我们的结果表明,主要是在OH-和O 2之后保留有碳-碳双键的异构体-加成进行单分子反应,其速率系数大到对大气重要。这极大地限制了潜在的重要单分子途径的数量。具体而言,我们发现开环的α-和β-pine烯异构体以及柠檬烯和萜品油烯的异构体具有足够快的单分子反应,从而有可能在大多数大气条件下支配它们的反应性。
更新日期:2020-04-03
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