Probative Evidence and Quantitative Energetics for the Unimolecular Mechanism of the 1,5-Sigmatropic Hydrogen Shift of Cyclopentadiene
Probative Evidence and Quantitative Energetics for the Unimolecular Mechanism of the 1,5-Sigmatropic Hydrogen Shift of Cyclopentadiene
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环戊二烯 1,5-Sigmatropic 氢转移单分子机制的证据和定量能量学
DOI：
10.1021/acs.joc.2c02145
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Houk, K. N.
中科院分区：
文献类型：
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作者：
Tran, Quan;Sengupta, Arkajyoti;Houk, K. N.
环戊二烯中的1，5-Sigmatrotic氢转移通常被认为是单分子周环反应，而Yamabe提出了一个更复杂的双分子机理，它是通过环戊二烯的外二聚体进行的。Yamabe的密度泛函计算表明，双分子机制在动力学上比单分子机制更有利。用ωB97X-D和DLPNO-CCSD(T)计算对单分子协同机制和Yamabe的双分子机制进行了重新研究，结果表明单分子机制相对于双分子机制有25千卡/摩尔的优势。虽然Yamabe的计算是用精度较低的B3LYP泛函进行的，但错误的结论是由于这里发现的另一个错误造成的。我们还计算了隧道效应的修正，其结果是计算的活化势垒在实验值的1.5千卡/摩尔以内。
While the 1,5-sigmatropic hydrogen shift in cyclopentadiene is generally thought to be a unimolecular pericyclic reaction, Yamabe proposed a more complex bimolecular mechanism proceeding through theexodimer of cyclopentadiene. DFT computations by Yamabe were claimed to show that the bimolecular mechanism was kinetically more favorable than the unimolecular mechanism. Reinvestigation of the unimolecular concerted mechanism and Yamabe’s bimolecular mechanism with ωB97X-D and DLPNO-CCSD(T) calculations demonstrates a 25 kcal/mol preference for the unimolecular mechanism relative to the bimolecular mechanism. While Yamabe’s calculations were performed with the less accurate B3LYP functional, the incorrect conclusion was the result of a different error discovered here. We have also computed corrections for tunneling that result in computed activation barriers within 1.5 kcal/mol of the experimental values.