Rapid Acceleration of Hydrogen Atom Abstraction Reactions of OH at Very Low Temperatures through Weakly Bound Complexes and Tunneling,Accounts of Chemical Research

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Rapid Acceleration of Hydrogen Atom Abstraction Reactions of OH at Very Low Temperatures through Weakly Bound Complexes and Tunneling
Accounts of Chemical Research ( IF 16.4 ) Pub Date : 2018-10-25 00:00:00 , DOI: 10.1021/acs.accounts.8b00304
Dwayne E. Heard ₁

Affiliation

A generally accepted principle of chemical kinetics is that a reaction will be very slow at low temperatures if there is an activation barrier on the potential energy surface to form products. However, this Account shows that the reverse is true for gas-phase hydrogen abstraction reactions of the hydroxyl radical, OH, with organic molecules with which it can form a weakly bound (5–30 kJ mol^–1) hydrogen-bonded complex. For hydrogen atom abstraction reactions of OH with volatile organic compounds (VOCs) containing alcohol, ether, carbonyl, and ester functional groups, the reaction accelerates rapidly at very low temperatures, with rate coefficients, k, that can be up to a 1000 times faster than those at room temperature, despite the barrier to products. The OH radical is a crucial intermediate in Earth’s atmosphere, combustion processes, and the chemistry of the interstellar medium, where temperatures can reach as low as 10 K, so this behavior has very important implications for gas-phase chemistry in space. The key point is that at low temperatures the lifetime of the OH–VOC complex against re-dissociation back to reactants becomes much longer, and hence the probability of quantum mechanical tunneling under the reaction barrier to form products becomes much higher.

中文翻译：

弱束缚配合物和隧穿在非常低的温度下快速加速OH的氢原子提取反应

化学动力学的普遍接受的原理是，如果在势能表面形成产物的活化势垒，则在低温下反应将非常缓慢。但是，这一说明表明，对于羟基自由基OH与有机分子的气相氢提取反应，情况恰恰相反，有机分子可与之形成弱键合（5–30 kJ mol ^–1）的氢键复合物。对于OH与包含醇，醚，羰基和酯官能团的挥发性有机化合物（VOC）的氢原子抽象反应，该反应在极低的温度下以速率系数k快速加速，尽管有产品障碍，但它可以比室温下的速度快1000倍。OH自由基是地球大气层，燃烧过程和星际介质化学反应中的关键中间体，在这些物质中温度可低至10 K，因此，这种行为对太空中的气相化学反应具有非常重要的意义。关键是在低温下，OH-VOC络合物防止再离解回到反应物的寿命变得更长，因此在反应势垒下形成产物的量子力学隧穿的可能性变得更高。

更新日期：2018-10-25

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