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首页> 外文期刊>Chemistry: A European journal >Correlated Rotation of the Me_3Si Groups in Tris(trimethylsilyl) methanes
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Correlated Rotation of the Me_3Si Groups in Tris(trimethylsilyl) methanes

机译：三（三甲基甲硅烷基）甲烷中Me_3Si基的相关旋转

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摘要

Low-temperature NMR spectra of (Me_3Si)_3CH (1) allowed the restricted rotation of the Me_3Si groups to be detected; the barrier was 5.1 kcal mol~(-1). On the basis of molecular mechanics calculations, this motion was assigned to a correlated disrotatory process with an eclipsed, staggered, staggered (ESS) transition state. In (Me_3Si)_3Cme (2), both a correlated ESS disrotatory process and a correlated conrotatory SSS process were distinguished, with rotational barriers of 6.7 and 5.15 kcal mol~(-1), respectively. Thus, 2 appears to adopt a chiral conformation (point group C_3) at low temperature. For more hindered derivatives such as (Me_3Si)_3CCH_2Me (3) and (Me_3Si)_3 CCH_2Et (4), the ESS and SSS processes involving rotation about the Si-C bonds were also detected, but in addition a third process became evident. This process corresponds to restricted rotation about the C-C bond and seems to be correlated with the SSS conrotatory process at the C-Si bond, since both display essentially the same barrier. Although in (Me_3Si)_3CCH_2Ph (5) the effects of restricted rotation about the C-CH_2Ph bond could not be observed, the same chiral conformation adopted by 3 and (point group C_1) was nonetheless assigned on the basis of molecular mechanics calculations and X-ray diffraction studies. The ~(13)C spectra (CPMAS) of crystalline 5 also showed that the pairs of ortho and meta phenyl carbon atoms are diastereotopic due to restricted Ph-CH_2 bond rotation in the solid state.
机译：（Me_3Si）_3CH（1）的低温NMR光谱可以检测到Me_3Si基团的旋转受限;势垒为5.1 kcal mol〜（-1）。在分子力学计算的基础上，将该运动分配给具有偏影，交错，交错（ESS）过渡状态的相关旋转过程。在（Me_3Si）_3Cme（2）中，区分了相关的ESS旋转过程和相关的旋转SSS过程，旋转势垒分别为6.7和5.15 kcal mol〜（-1）。因此，2在低温下似乎具有手性构象（点组C_3）。对于（Me_3Si）_3CCH_2Me（3）和（Me_3Si）_3 CCH_2Et（4）等受阻衍生物，也检测到涉及围绕Si-C键旋转的ESS和SSS过程，但除此之外，第三个过程也很明显。该过程对应于围绕C-C键的受限旋转，并且似乎与C-Si键处的SSS旋转过程相关，因为两者都显示出基本相同的势垒。尽管在（Me_3Si）_3CCH_2Ph（5）中无法观察到绕C-CH_2Ph键旋转受限的影响，但仍基于分子力学计算和X分配了3和（点组C_1）采用的相同手性构象射线衍射研究。晶体5的〜（13）C光谱（CPMAS）还显示，由于固态中的Ph-CH_2键旋转受限制，邻位和间位苯基碳原子对为非对映体。

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