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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Dynamics of 1, 2-Hydrogen Migration in Carbenes and Ring Expansion in Cyclopropylcarbenes
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Dynamics of 1, 2-Hydrogen Migration in Carbenes and Ring Expansion in Cyclopropylcarbenes

机译：卡宾苯中1、2-氢迁移和环丙基卡宾环扩环的动力学

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摘要

Variational transition state theory with multidimensional tunneling contributions has been used to calculate the rate constants, kinetic isotope effects, and activation energies for 1, 2-shifts in methylchlorocarbene, benzylchlorocarbene, cyclopropylfluorocarbene, and cyclopropylchlorocarbene. Calculations have been performed for the rearrangements both in the gas phase and in various solvents. Including solvation effects reduces the calculated activation barrier for each of these reactions. The effects of quantum mechanical tunneling are computed to be significant for the 1, 2-hydrogen migrations and to be bigger for hydrogen than for deuterium. Consequently, the deuterium kinetic isotope effects are predicted to be relatively large but to decrease with increasing temperature. In contrast, tunneling is not calculated to play a significant role in either of the halocyclopropylcarbene rearrangements, which both involve the 1, 2-shift of a CH_2 group. Thus, heavy-atom tunneling is apparently not responsible for the fact that the calculated activation parameters are very different from experiment for cyclopropylfluorocarbene, with the experimental activation enthalpy much smaller than the calculated one and the experimental activation entropy much more negative than the computed value. Possible causes for the large differences between the calculated and measured activation parameters are discussed.
机译：具有多维隧穿贡献的变分过渡态理论已用于计算速率常数，动力学同位素效应和甲基氯卡宾，苄基氯卡宾，环丙基氟卡宾和环丙基氯卡宾中1、2位移的活化能。已经对气相和各种溶剂中的重排进行了计算。包括溶剂化作用将减少这些反应中每一个的计算活化障碍。计算得出的量子力学隧穿效应对1,2-氢迁移很重要，对氢的影响大于对氘的影响。因此，预计氘的动力学同位素效应相对较大，但随着温度升高而降低。相反，未计算出隧穿在任何卤代环丙基卡宾重排中都起重要作用，这两者均涉及CH_2基团的1、2-移位。因此，重原子隧穿显然不对以下事实负责：计算出的活化参数与环丙基氟碳烯的实验差异很大，实验活化焓比计算值小得多，实验活化熵比计算值大得多。讨论了计算出的激活参数与测量到的激活参数之间差异较大的可能原因。

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