Understanding Substituent Effects on 29Si Chemical Shifts and Bonding in Disilynes. A Quantum-Chemical Analysis
Understanding Substituent Effects on 29Si Chemical Shifts and Bonding in Disilynes. A Quantum-Chemical Analysis
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了解取代基对二硅烷中 29Si 化学位移和成键的影响。
DOI：
10.1021/om050499b
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发表时间：
2003
期刊：
影响因子：
2.8
通讯作者：
C. Strohmann
中科院分区：
文献类型：
--
作者：
D. Auer;A. Kaupp;C. Strohmann
29 Si取代的二硅炔的化学位移进行了分析，通过量子化学研究，使用的顺磁贡献到耦合的占用和虚拟的正则分子轨道的详细故障。结果表明了取代基对屏蔽效应的影响，并证实了对称取代二硅炔（H3 SiSiSiH 3和H3CSiSiCH 3）的σp方程中能量因子对化学位移的重要性.在不对称取代的二硅炔H3CSiSiH 3中，两个位点的能量转换因子是相同的，因此不能解释化学位移的巨大差异。事实证明，不对称的电荷分布（反映在占用和虚拟MO和采样的PSO矩阵元素）允许更有效的耦合在甲基取代的硅侧。此外，二硅炔的屏蔽值强烈地依赖于trans-bent角φ的大小，这一点通过对H3 SiSiSiH 3模型中29 Si化学位移的分析清楚地表明。
The 29Si chemical shifts in substituted disilynes have been analyzed by quantum-chemical studies using a detailed breakdown of paramagnetic contributions into couplings of occupied and virtual canonical molecular orbitals. The results give indications of substituent effects on shielding and confirm the importance of energy denominators in the equation for σp in symmetrical substituted disilynes (H3SiSiSiSiH3 and H3CSiSiCH3) on their chemical shifts. In the unsymmetrical substituted disilyne H3CSiSiSiH3 the energy denominators are identical for both sites and thus cannot explain the widely different chemical shifts. It turns out that the asymmetric charge distribution (reflected in both occupied and virtual MOs and sampled by the PSO matrix elements) allows more efficient couplings at the methyl-substituted silicon side. Furthermore, shielding values in disilynes depend strongly on the size of the trans-bent angle φ, as indicated clearly by analyses of the 29Si chemical shifts in the model H3SiSiSiSiH3 at ...