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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Molecular Structure, Equilibrium Conformation, and Ring-Puckering Motion in 1,1,3,3-Tetramethylcyclobutane. An Electron-Diffraction Investigation Augmented by Molecular Orbital and Normal Coordinate Calculations
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Molecular Structure, Equilibrium Conformation, and Ring-Puckering Motion in 1,1,3,3-Tetramethylcyclobutane. An Electron-Diffraction Investigation Augmented by Molecular Orbital and Normal Coordinate Calculations

机译：在1,1,3,3-四甲基环丁烷中的分子结构，平衡构象和环形褶皱运动。 通过分子轨道和正常坐标计算增强的电子衍射调查

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The molecule cyclobutane (CB) has a non planar carbon skeleton folded around a line connecting diagonally opposite atoms. The puckering angle (the change from planarity) of similar to 30 degrees is generally attributed to steric repulsion between the four sets of adjacent methylene groups that would be opposed in a planar ring and is relieved by the puckering. According to this criterion, a similar molecule, 1,1,3,3-tetramethylcyclobutene (TMCB), in which adjacent methylene groups do not exist, would be expected to have a planar ring in the equilibrium form. We have investigated the structure of TMCB to test this expectation. Two models were designed for the tests: one having D-2h symmetry (planar ring) and one of C-2v symmetry (nonplanar ring). Each model incorporated the dynamics of large-amplitude bending around a line joining the methylene groups. Our results suggest the D-2h model is to be preferred. Dynamic averages (r(g)/angstrom; <(g)/deg) of the more important distances and angles in the D-2h model with estimated 2 sigma uncertainties, are as follows. = 1.105 (5), C1-C5 = 1.524 (10), C1-C2 = 1.559 (11), C2-C1-C4 = 87.4 (8), C1-C2-C3 = 92.0 (7), C5-C1-C6 = 109.0 (13), and C5-C1-C5 = 115.8 (8). The large-amplitude bending of the ring leads to a thermal average value of the folding angle equal to 177.1 degrees. The results, including the differences between TMCB and CB, are discussed.
机译：分子环丁烷（Cb）具有围绕连接对角线相对原子的线折叠的非平面碳骨架。与30度相似的褶皱角度（平面变化）通常归因于在平面环中相对的四组相邻的亚甲基之间的空间排斥，并且通过褶皱释放。根据该标准，预期相邻亚甲基的类似分子，1,1,3,3-四甲基环丁烯（TMCB），其中相邻的亚甲基亚亚甲基将有平衡形式的平面环。我们研究了TMCB的结构来测试这一期望。设计了两种型号用于测试：一个具有D-2H对称性（平面环）和C-2V对称（非平面环）之一。每个模型都包含了加入亚甲基的线的大振幅弯曲的动态。我们的结果表明D-2H模型是首选。动态平均值（R（g）/ angstrom; <（g）/ deg）的D-2H模型中的更重要的距离和角度，估计为2 sigma不确定性，如下所示。 = 1.105（5），C1-C5 = 1.524（10），C1-C2 = 1.559（11），C2-C1-C4 = 87.4（8），C1-C2-C3 = 92.0（7），C5 -C1-C6 = 109.0（13）和C5-C1-C5 = 115.8（8）。环的大幅度弯曲导致折叠角的热平均值等于177.1度。讨论了包括TMCB和CB之间的差异的结果。

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