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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Investigating the Dynamics of Carbanion Protonation by Means of Laser Flash Electron Photoinjection from an Electrode
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Investigating the Dynamics of Carbanion Protonation by Means of Laser Flash Electron Photoinjection from an Electrode

机译：通过电极上的激光闪光电子光注入研究碳负离子质子的动力学

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摘要

The investigation of protonation/deprotonation at carbon is traditionally limited to molecules where acidity has been boosted by introduction of an electron-withdrawing group or by removal of an electron. These restrictions can be removed by application of the laser flash electron photoinjection technique. A thin layer of radicals is initially formed upon reduction of an appropriate substrate by the photoinjected electrons. The time-resolved current-potential responses for the reduction of the radicals thus generated are sensitive to the rate of the protonation of the ensuing carbanion by purposely added acids. The second-order rate constant may then the extracted from the half-wave potential versus time data with satisfactory accuracy in a wide range of values that extends up to the diffusion limit. The method is demonstrated with the example of diphenylmethyl and benzyl carbanions. Several observations may be derived from these first illustrating experiments. There is a large kinetic isotope effect. Proton transfer is intrinsically slow, showing that this property is not the result of the presence of an electron-withdrawing group. The intrinsic barrier is larger in the benzyl case than in the diphenylmethyl case. Unusual temperature effects (negative activation enthalpy) are observed at least in some cases, calling for systematic investigation in future studies.
机译：传统上，对碳质子化/去质子化的研究仅限于通过引入吸电子基团或通过除去电子来提高酸度的分子。这些限制可以通过应用激光闪光电子光注入技术消除。在通过光注入的电子还原适当的基底之后，首先形成自由基的薄层。对于如此产生的自由基的还原，时间分辨的电流电势响应对随后有意添加的酸的碳负离子的质子化速率敏感。然后可以在扩展到扩散极限的宽范围的值中以令人满意的精度从半波电势对时间数据中提取二阶速率常数。以二苯基甲基和苄基碳负离子为例演示了该方法。从这些最初的说明性实验中可以得出一些观察结果。有很大的动力学同位素效应。质子转移本质上是缓慢的，表明该性质不是吸电子基团的存在的结果。在苄基情况下，本征势垒比在二苯甲基情况下大。至少在某些情况下观察到异常的温度效应（负激活焓），需要在以后的研究中进行系统的研究。

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