A theory that connects proton-coupled electron-transfer and hydrogen-atom transfer reactions
A theory that connects proton-coupled electron-transfer and hydrogen-atom transfer reactions
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DOI：
10.1021/jp012396m
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发表时间：
2002-02-21
影响因子：
3.3
通讯作者：
Cukier, RI
中科院分区：
文献类型：
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作者：
Cukier, RI
质子耦合电子转移 (PCET) 反应的理论 (Cukier, R. I., Nocera, D. Ann. Rev. Phys. Chem. 1998, 49, 337) 被推广到也适用于氢原子转移 (HAT) 反应。 PCET被描述为电子和质子的协同转移，两种物质在各自的初始状态和最终状态之间弱耦合，这是电子和质子的非绝热状态。在这里，我们绝热地对待电子，断言它是强耦合的，并且质子可以跨越非绝热到绝热区域。获得了速率常数表达式，其中包含了围绕转移氢原子的重原子骨架动力学以及内球振动模式的影响。出现的速率常数的特征是通常可以预期适度的同位素效应。一些氢原子转移反应具有小速率常数、小活化能和相对较小的同位素效应的观察结果可以基于该理论来理解。氮酸和含氧酸与碳酸之间的对比动力学性质也可以合理化。
A theory for proton-coupled electron-transfer (PCET) reactions (Cukier, R. I., Nocera, D. Ann. Rev. Phys. Chem. 1998, 49, 337) is generalized to also apply to hydrogen-atom transfer (HAT) reactions. PCET was described as a concerted transfer of an electron and proton, with both species weakly coupled between their respective initial and final states, a nonadiabatic regime for both electron and proton. Here, we treat the electron adiabatically, asserting that it is strongly coupled and the proton can span the nonadiabatic to adiabatic regimes. A rate constant expression is obtained that incorporates the heavy-atom framework dynamics surrounding the transferring hydrogen atom as well as the effects of inner-sphere vibrational modes. Features of the rate constant that emerge are that modest isotope effects are often to be expected. The observation that some hydrogen-atom transfer reactions have small rate constants, small activation energies, and relatively small isotope effects can be understood on the basis of this theory. The contrasting kinetic properties between nitrogen and oxygen acids versus carbon acids can also be rationalized.