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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Modern Valence Bond Description of the Electronic Mechanisms of S_N2 Identity Reactions
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Modern Valence Bond Description of the Electronic Mechanisms of S_N2 Identity Reactions

机译：S_N2身份反应电子机制的现代价键描述

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摘要

Series of ab initio modern valence bond calculations, based on spin-coupled (SC) theory, along the MP2(fc)/6-31G(d,p) minimum-energy paths, are used to examine the electronic rearrangements that take place during the gas-phase S_N2 identity reactions of Cl~- with RCl, where R is methyl, ethyl, or tert-butyl. The corresponding reaction of F~- with CH_3F is also considered. The SC descriptions of the two CH_3X + X~- reactions (X = F or Cl) are found to be qualitatively similar, but there is a significantly larger extent of bond formation at the transition state for the fluorine case, and the electronic rearrangements also start much sooner. Comparing CH_3Cl + Cl~- and CH_3CH_2Cl + Cl~-, the SC calculations suggest that the electronic structure reorganization is largely unaffected by the presence of the additional methyl group. The description of the transition state for the corresponding gas-phase S_N2 identity reaction of (CH_3)_3CCl is found to be radically different: it is held together by predominantly ionic interactions and most closely resembles a carbocation "clamped" between two chloride ions.
机译：基于自旋耦合（SC）理论，沿着MP2（fc）/ 6-31G（d，p）最小能量路径进行的一系列从头算现代价键计算，用于检查在过程中发生的电子重排Cl-与RCl的气相S_N 2身份反应，其中R为甲基，乙基或叔丁基。还考虑了F〜-与CH_3F的相应反应。发现两个CH_3X + X〜-反应（X = F或Cl）的SC描述在质量上相似，但是对于氟的情况，过渡态的键形成程度明显更大，并且电子重排也早点开始。比较CH_3Cl + Cl〜-和CH_3CH_2Cl + Cl〜-，SC计算表明，电子结构重组在很大程度上不受附加甲基的影响。发现对（CH_3）_3CCl的相应气相S_N2身份反应的过渡态的描述是根本不同的：它通过主要的离子相互作用保持在一起，并且非常类似于两个氯离子之间“钳位”的碳正离子。

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