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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Deciphering the NMR Fingerprints of the Disordered System with Quantum Chemical Studies
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Deciphering the NMR Fingerprints of the Disordered System with Quantum Chemical Studies

机译：用量子化学研究破译无序系统的NMR指纹图谱

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摘要

Recent developments in solid-state NMR techniques helped acquire high-resolution NMR spectra for solid systems with structural disorder. But the structural origin of the observed chemical shift nonequivalence in these systems has not been revealed. We report a quantum chemical investigation of the solid-state NMR spectrum in N,N-bis(diphenylphosphino)-N-((S)-R-methylbenzyl)amine, where eight nonequivalent 31P NMR chemical shifts were resolved with a range of 13.0 ppm. Results from using different quantum chemical methods, computational algorithms, intermolecular effects, and structures indicate that for the disordered system, geometry optimization gives the best accord with experimental NMR chemical shifts, which has a theory-versus-experiment correlation R2 ) 0.949 and SD ) 1.1 ppm, or R2 ) 0.994 and SD ) 0.4 ppm when the average of two unassigned NMR shifts for each molecule is used. In addition, these calculations indicate that the experimental chemical shift nonequivalence in this system is mainly a consequence of the different geometries around the phosphorus atoms due to disordered environments. The experimental 31P NMR chemical shifts are well correlated (R2 ) 0.981) with two conformation angles and one bond length, each associated with one of the three bonding interactions around the phosphorus atoms. These results will facilitate the use of quantum chemical techniques in structural characterization of disordered solids and elucidation of NMR properties.
机译：固态NMR技术的最新发展有助于获得具有结构紊乱的固体系统的高分辨率NMR光谱。但是，尚未揭示在这些系统中观察到的化学位移不等价的结构起源。我们报告了在N，N-双（二苯基膦基）-N-（（S）-R-甲基苄基）胺中的固态NMR光谱的量子化学研究，其中八个非等效的31P NMR化学位移被解析为13.0 ppm。使用不同的量子化学方法，计算算法，分子间效应和结构的结果表明，对于无序系统，几何优化最符合实验NMR化学位移，其理论与实验的相关性为R2）0.949和SD）当使用每个分子的两个未分配的NMR位移的平均值时，则为1.1 ppm或R2）0.994和SD）0.4 ppm。此外，这些计算表明，该系统中实验化学位移的不等价性主要是由于环境混乱造成的磷原子周围几何形状不同的结果。实验的31P NMR化学位移与两个构象角和一个键长相关性良好（R2）0.981），每个构型角与磷原子周围的三个键合相互作用之一相关。这些结果将有助于量子化学技术在无序固体的结构表征和NMR特性的阐明中的应用。

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