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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Determination of ~(29)Si-~1H spin-spin coupling constants in organoalkoxysilanes with nontrivial scalar coupling patterns
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Determination of ~(29)Si-~1H spin-spin coupling constants in organoalkoxysilanes with nontrivial scalar coupling patterns

机译：具有非平凡标量耦合模式的有机烷氧基硅烷中〜（29）Si-〜1H自旋自旋耦合常数的测定

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摘要

Application of polarization transfer techniques such as DEPT and INEPT in ~(29)Si NMR investigation of bridged silane polymerization requires knowledge of indirect ~(29)Si-~1H scalar coupling constants in the silane system. However, the fully coupled ~(29)Si NMR spectra of these molecules, specifically those containing ethylene bridging groups, are too complicated to measure the coupling constants directly by visual inspection. This is because unlike hydrocarbon systems where one-bond proton-carbon coupling constants exceed other coupling constants by an order of magnitude, in silanes the closest proton-silicon pairs are separated by two bonds and all coupling coefficients (both homonuclear and heteronuclear) are of similar magnitude. In these systems, theoretical tools are required to interpret the spectra of even simple molecules. Here, we determine density functional theory estimates of ~(29)Si-~1H scalar coupling constants and use these along with homonuclear coupling constant estimates to resolve the nontrivial nature of these spectra. We also report a Karplus equation consistent with the dihedral angle dependence of the three-bond homo- and heteronuclear coupling in the ethylene bridge. By thermal averaging of DFT coupling constants, a good initial guess of the coupled ~(29)Si spectral pattern is made, which is easily refined by curve fitting to determine estimates of all coupling constants in the system.
机译：极化转移技术（如DEPT和INEPT）在桥接硅烷聚合的〜（29）Si NMR研究中的应用需要了解硅烷体系中间接〜（29）Si-〜1H标量耦合常数。然而，这些分子，特别是那些含有乙烯桥联基团的分子的完全偶合〜（29）Si NMR光谱太复杂，以至于无法通过目测直接测量偶合常数。这是因为与烃体系中单键质子-碳偶合常数超过其他偶合常数一个数量级的烃类系统不同，在硅烷中，最接近的质子-硅对被两个键分开，并且所有偶合系数（均核和异核）均为相似的幅度。在这些系统中，需要理论工具来解释甚至简单分子的光谱。在这里，我们确定〜（29）Si-〜1H标量耦合常数的密度泛函理论估计，并将它们与同核耦合常数估计一起使用以解决这些光谱的非平凡性质。我们还报告了一个Karplus方程，该方程与乙烯桥中三键同核和异核偶联的二面角依赖性相关。通过对DFT耦合常数进行热平均，可以很好地估计耦合的〜（29）Si光谱图，可以通过曲线拟合轻松地确定其光谱，以确定系统中所有耦合常数的估计值。

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