Atmospheric Oxidation Mechanism of Sabinene Initiated by the Hydroxyl Radicals
Atmospheric Oxidation Mechanism of Sabinene Initiated by the Hydroxyl Radicals
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羟基自由基引发桧烯的大气氧化机理
DOI：
10.1021/acs.jpca.8b06381
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发表时间：
2018
影响因子：
2.9
通讯作者：
Wang Liming
中科院分区：
文献类型：
--
作者：
Wang Lingyu;Wang Liming
采用量子化学计算方法，在CBS-QB 3水平上研究了OH自由基引发桧烯大气氧化的机理，并采用过渡态理论和单分子速率理论结合碰撞能量转移计算了反应动力学.通过比较桧烯和桧酮与OH自由基反应的速率系数，估算出氧化反应是由OH自由基加成到CH_2-C_（<1）键上引发的，其支化率为100（92-96）%，而所有的氢原子夺取占支化率的100（4-8）%. OH加成到C1-C6碳上形成自由基加合物Ra，而OH加成到末端CH 2-C6碳上形成自由基加合物Rb，其将迅速且几乎完全地使三元环断裂成自由基Re。RRKM-ME计算得到的分数产率为0.40，0.09，和0.51的radicalssyn-Ra，反Ra，和Re，分别在298 K和760托。在大气中，thesyn/anti-Ra自由基将最终转化为sabinaketone在ppbv水平的NO的存在下，而在Re自由基的转化，双分子反应和单分子H-迁移可以发生竞争形成的过氧自由基。过氧自由基中的H-迁移导致形成含有>C = O、−OH和/或−OOH基团的不饱和多官能化合物。在高NO存在下，预测顺式和反式Ra生成桧酮，Re生成丙酮，产率分别为0.37和0.38，大于实验值0.19-0.23和0.21-0.27，但与实验值相当一致。
The atmospheric oxidation mechanism of sabinene initiated by the OH radical has been studied using quantum chemistry calculations at the CBS-QB3 level and reaction kinetic calculations using transition state theory and unimolecular rate theory coupled with collisional energy transfer. The oxidation is initiated by OH radical additions to the CH2═C< bond with a branching ratio of ∼(92–96)%, while all the hydrogen atom abstractions count for ∼(4–8)% of branching ratio, which was estimated by comparing the rate coefficients of the reactions of sabinene and sabinaketon with the OH radical. Addition of OH to the ═C< carbon forms radical adduct Ra, while addition of OH to the terminal CH2═ carbon forms radical adduct Rb, which would break the three-membered ring promptly and almost completely to radical Re. RRKM-ME calculations obtained fractional yields of 0.40, 0.09, and 0.51 for radicalssyn-Ra,anti-Ra, and Re, respectively, at 298 K and 760 Torr. In the atmosphere, thesyn/anti-Ra radical would ultimately transform to sabinaketone in the presence of ppbv levels of NO, while in the transformation of the Re radical, both bimolecular reactions and unimolecular H-migrations could occur competitively for the peroxy radicals formed. The H-migrations in peroxy radicals result in the formation of unsaturated multifunctional compounds containing >C═O, −OH, and/or −OOH groups. Formation of sabinaketone fromsyn- andanti-Ra and formation of acetone from Re are predicted with yields of ∼0.37 and ∼0.38 in the presence of high NO, being larger than while in reasonable agreement with the experimental values of 0.19–0.23 and of 0.21–0.27, respectively.