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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Solution and solid-state effects on NMR chemical shifts in sesquiterpene lactones: NMR, X-ray, and theoretical methods
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Solution and solid-state effects on NMR chemical shifts in sesquiterpene lactones: NMR, X-ray, and theoretical methods

机译：倍半萜烯内酯对NMR化学位移的固溶和固相影响：NMR，X射线和理论方法

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摘要

Selected guaianolide type sesquiterpene lactones were studied combining solution and solid-state NMR spectroscopy with theoretical calculations of the chemical shifts in both environments and with the X-ray data. The experimental ~1H and ~(13)C chemical shifts in solution were successfully reproduced by theoretical calculations (with the GIAO method and DFT B3LYP 6-31++G) after geometry optimization (DFT B3LYP 6-31 G) in vacuum. The GIPAW method was used for calculations of solid-state ~(13)C chemical shifts. The studied cases involved two polymorphs of helenalin, two pseudopolymorphs of 6α-hydroxydihydro-aromaticin and two cases of multiple asymmetric units in crystals: one in which the symmetry-independent molecules were connected by a series of hydrogen bonds (geigerinin) and the other in which the symmetry-independent molecules, deprived of any specific intermolecular interactions, differed in the conformation of the side chain (badkhysin). Geometrically different molecules present in the crystal lattices could be easily distinguished in the solid-state NMR spectra. Moreover, the experimental differences in the ~(13)C chemical shifts corresponding to nuclei in different polymorphs or in geometrically different molecules were nicely reproduced with the GIPAW calculations.
机译：结合溶液和固态NMR光谱以及在两种环境下化学位移的理论计算以及X射线数据，研究了所选的瓜亚内酯型倍半萜烯内酯。在真空中进行几何优化（DFT B3LYP 6-31 G）后，通过理论计算（使用GIAO方法和DFT B3LYP 6-31 ++ G）成功地再现了溶液中〜1H和〜（13）C的实验化学位移。 GIPAW方法用于计算固态〜（13）C化学位移。研究的案例涉及Helenalin的两个多态性，6α-羟基二氢-芳香族化合物的两个假多态性和晶体中多个不对称单元的两个案例：一个通过两个氢键（geigerinin）连接不对称的分子，另一个在被剥夺任何特定分子间相互作用的非对称对称分子的侧链构象不同（badkhysin）。存在于晶格中的几何上不同的分子可以在固态NMR光谱中轻松区分。此外，GIPAW计算很好地再现了对应于不同多晶型物或几何形状不同分子的核的〜（13）C化学位移的实验差异。

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