Solvent-dependent transition states for decarboxylations.
Solvent-dependent transition states for decarboxylations.
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DOI：
10.1021/ja010791k
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发表时间：
2001-07
影响因子：
15
通讯作者：
D. Sicińska;D. Truhlar;P. Paneth
中科院分区：
文献类型：
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作者：
D. Sicińska;D. Truhlar;P. Paneth
4-吡啶乙酸脱羧反应的速率常数和动力学同位素效应强烈依赖于溶剂是水还是二氧六环，本文解释了这一发现。我们计算溶剂依赖的自由能垒和（13）C和（18）O的动力学同位素效应，使用基于IV类电荷和半经验原子表面张力的量子力学溶剂化模型。计算结果提供了一致的解释的实验结果，这提供了一个惊人的确认的合理性的溶剂化建模。更重要的是，理论和实验的一致性使我们对模型提供的反应物理图像充满信心。这表明，过渡态的位置，如断裂C-C键的长度所测量的，在二氧六环中比气相晚0.24 A，在水中比气相晚0.37 A。过渡态的电荷发展也强烈依赖于溶剂;特别是CO（2）部分在二氧六环中的过渡态比在水中负0.07个电子电荷单位。
The rate constants and kinetic isotope effects for decarboxylation of 4-pyridylacetic acid depend strongly on whether the solvent is water or dioxane, and the present paper interprets this finding. We calculate the solvent dependence of the free energy barrier and of the (13)C and (18)O kinetic isotope effects using a quantum mechanical solvation model based on class IV charges and semiempirical atomic surface tensions. The calculations provide a consistent interpretation of the experimental results, which provides a striking confirmation of the soundness of the solvation modeling. Even more significantly, the agreement of theory and experiment gives us confidence in the physical picture of the reaction provided by the model. This indicates that the location of the transition state, as measured by the length of the breaking C--C bond, is 0.24 A later than the gas phase in dioxane and 0.37 A later than the gas phase in water. Charge development at the transition state also depends strongly on the solvent; in particular the CO(2) moiety is 0.07 electronic charge units more negative at the transition state in dioxane than in water.