Investigation of the polymorphs of dimethyl-3,6-dichloro-2,5-dihydroxyterephthalate by (13)C solid-state NMR spectroscopy.
Investigation of the polymorphs of dimethyl-3,6-dichloro-2,5-dihydroxyterephthalate by (13)C solid-state NMR spectroscopy.
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通过 (13)C 固态核磁共振波谱研究 3,6-二氯-2,5-二羟基对苯二甲酸二甲酯的多晶型物。
DOI：
10.1021/ja003599b
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发表时间：
2001
影响因子：
15
通讯作者：
Grant,DM
中科院分区：
文献类型：
--
作者：
Strohmeier,M;Orendt,AM;Alderman,DW;Grant,DM
本文用固体核磁共振技术研究了3，6-二氯-2，5-二羟基对苯二甲酸二甲酯的三种构象多晶型中的两种。多晶型物之间的结构差异先前已通过X射线进行了研究。在这两种多晶型物中，由于它们的颜色而被命名为白色和黄色，主要的结构差异是酯基和芳环之间的扭转角。黄色形式在芳环平面和酯基平面之间具有4°的二面角，而白色形式在每个晶胞中具有两个不同的分子，二面角为70°和85°。这种变化极大地影响了π电子系统中的共轭。此外，氢键模式也有差异，白色形式具有分子间氢键，黄色形式具有分子内氢键。本文从13 C MAS谱中提取了碳各向同性化学位移值和氯电场梯度（EFG）张量信息，并从二维FIREMAT实验中获得了碳的化学位移张量主值。在HF和DFT理论水平上对单个分子和三个分子的堆叠进行化学位移张量数据以及EFG张量的量子化学计算，以解释白色形式的重要分子间相互作用。两种多晶型物的光谱数据之间的差异进行了讨论，在已知的电子和结构的差异。
Two of the three conformational polymorphs of dimethyl-3,6-dichloro-2,5-dihydroxyterephthalate are studied by solid-state NMR techniques. The structural differences between the polymorphs have previously been studied by X-ray. In these two polymorphs named white and yellow due to their color, the major structural difference is the torsional angle between the ester group and the aromatic ring. The yellow form has a dihedral angle of 4° between the plane of the aromatic ring and the plane of the ester group, while the white form has two different molecules per unit cell with dihedral angles of 70° and 85°. This change greatly affects the conjugation in the π-electronic system. In addition, there are differences in the hydrogen-bonding patterns, with the white form having intermolecular hydrogen bonds and the yellow form having intramolecular hydrogen bonds. In this work, the carbon isotropic chemical shift values and the chlorine electric field gradient (EFG) tensor information are extracted from the13C MAS spectra, and the principal values of the chemical shift tensors of the carbons are obtained from 2D FIREMAT experiments. Quantum chemical calculations of the chemical shift tensor data as well as the EFG tensor are performed at the HF and DFT levels of theory on individual molecules and on stacks of three molecules to account for the important intermolecular interactions in the white form. The differences between the spectral data on the two polymorphs are discussed in terms of the known electronic and structural differences.