Structure assignment in the solid state by the coupling of quantum chemical calculations with NMR experiments: a columnar hexabenzocoronene derivative.
Structure assignment in the solid state by the coupling of quantum chemical calculations with NMR experiments: a columnar hexabenzocoronene derivative.
复制标题
DOI：
10.1021/ja0021823
复制
发表时间：
2001-02
影响因子：
15
通讯作者：
Christian Ochsenfeld;Steven P. Brown;I. Schnell;J. Gauss;Hans W. Spiess
中科院分区：
文献类型：
--
作者：
Christian Ochsenfeld;Steven P. Brown;I. Schnell;J. Gauss;Hans W. Spiess
我们提出了一个量子化学从头算研究，这表明了一个新的实验和理论相结合的方法，从而比较计算和实验的（1）H NMR化学位移允许在固态分子系综的结构安排的说明，利用（1）H化学位移的显着敏感性，分子间的相互作用。最近，Brown等人已经表明，在35 kHz的快速魔角旋转（MAS）下，烷基取代的六苯并晕苯（HBC）衍生物的固相的（1）H NMR谱的分辨率足以观察到迄今为止三种不同的芳族共振的出乎意料的分辨率（J.Am.Chem.2004）。1999，121，6712）。利用由（1）H双量子（DQ）MAS NMR光谱提供的关于质子邻近性的额外信息，结果表明，结果与以类似于未取代的HBC中的方式的芳族核堆积定性一致。以HBC-C（12）分子为例，我们在这里表明，新的实验和理论相结合的方法允许观察到的（1）H化学位移以定量的方式与分子间结构相关。在量子化学计算中，使用了一系列堆叠的HBC低聚物模型系统。由于（1）H化学位移对附近芳环产生的环电流有显著的依赖性，计算的（1）H化学位移对HBC分子的堆积排列非常敏感。此外，发现环电流效应的范围特别长，观察到距离700 pm的第二个邻居的相当大的影响。
We present a quantum chemical ab initio study which demonstrates a new combined experimental and theoretical approach, whereby a comparison of calculated and experimental (1)H NMR chemical shifts allows the elucidation of structural arrangements in solid-state molecular ensembles, taking advantage of the marked sensitivity of the (1)H chemical shift to intermolecular interactions. Recently, Brown et al. have shown that, under fast magic-angle spinning (MAS) at 35 kHz, the resolution in a (1)H NMR spectrum of the solid phase of an alkyl-substituted hexabenzocoronene (HBC) derivative is sufficient to observe the hitherto unexpected resolution of three distinct aromatic resonances ( J. Am. Chem. Soc. 1999, 121, 6712). Exploiting the additional information about proton proximities provided by (1)H double-quantum (DQ) MAS NMR spectroscopy, it was shown that the results are qualitatively consistent with the aromatic cores packing in a manner similar to that in unsubstituted HBC. Using the HBC-C(12) molecule as an example, we show here that the new combined experimental and theoretical approach allows the observed (1)H chemical shifts to be related in a quantitative manner to the intermolecular structure. In the quantum chemical calculations, a series of model systems of stacked HBC oligomers are used. On account of the marked dependence of the (1)H chemical shift to ring currents arising from nearby aromatic rings, the calculated (1)H chemical shifts are found to be very sensitive to the stacking arrangement of the HBC molecules. Moreover, the ring current effect is found to be particularly long range, with a considerable influence of the second neighbor, at a distance of 700 pm, being observed.