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Origin of the Thermodynamic Stability of the Polymorph IV of Crystalline Barbituric Acid: Evidence from Solid-State NMR and Electron Density Analyses

机译:晶体巴比妥酸多晶型物IV热力学稳定性的起源:来自固态NMR和电子密度分析的证据

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摘要

In this contribution, the origin of the stability of the polymorph IV (enol form) of crystalline barbituric acid relative to the polymorph II (keto form) is investigated using solid-state NMR spectroscopy and electron density analysis. Electron density analysis reveals differences in the nature of the intermolecular contacts in the different polymorphs of barbituric acid. Comparing the properties of hypothetical single molecules of barbituric acid with cluster models shows that the electronic and magnetic properties of polymorphs of barbituric acid can be employed to measure the strengths of the intermolecular interactions. Changes in the magnitudes of the NMR chemical shift tensors are also shown to be parallel to the intermolecular delocalization index of Quantum Theory of Atoms in Molecules, which measures the covalency of an intermolecular interaction.
机译:在该贡献中,使用固态NMR光谱法和电子密度分析研究了结晶巴比妥酸的多晶型物IV(烯醇形式)相对于多晶型物II(酮形式)的稳定性的起源。电子密度分析揭示了巴比妥酸的不同多晶型中分子间接触的性质的差异。将假设的巴比妥酸单分子的性质与聚类模型进行比较表明,巴比妥酸多晶型物的电子和磁性可以用来测量分子间相互作用的强度。 NMR化学位移张量的大小变化也显示与分子中原子量子论的分子间离域指数平行,该指数测量了分子间相互作用的共价性。

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