Ashizawa K
Department of Physical Chemistry, Eisai Company, Ltd., Ibaragi, Japan.
J Pharm Sci. 1989 Mar;78(3):256-60. doi: 10.1002/jps.2600780318.
Two polymorphic forms, alpha and beta, of 2R,4S,6-fluoro-2-methyl-spiro-[chroman-4,4'-imidazoline]-2',5-dione (1, M79175) were studied by X-ray crystallography and solid-state infrared spectroscopy. The molecular and crystal structures of the beta-form were determined by single-crystal X-ray diffraction analysis. The molecules in the beta-form crystal are arranged orderly along the b-axis, and the plate-like moieties (chroman ring) of 1 are stacked by van der Waals forces. The molecular packing structure of each crystalline form was investigated by comparing wave numbers of hydantoin rings from which solid-state infrared photoacoustic spectra (FT-IR-PAS) were obtained. From the FT-IR-PAS data of both forms, it became clear that the hydrogen bond in an alpha-form crystal is stronger than that in the beta-form crystal. The cohesion of the polymorphic crystal system is mainly due to hydrogen bonds and van der Waals forces. Based on the polymorphism of 1, it was clarified that thermodynamic stability depends on the mode of hydrogen bonding, while the enthalpy of fusion results from van der Waals forces.
通过X射线晶体学和固态红外光谱对2R,4S,6-氟-2-甲基-螺[苯并二氢吡喃-4,4'-咪唑啉]-2',5-二酮（1，M79175）的两种多晶型形式α和β进行了研究。通过单晶X射线衍射分析确定了β型的分子和晶体结构。β型晶体中的分子沿b轴有序排列，1的板状部分（苯并二氢吡喃环）通过范德华力堆积。通过比较获得固态红外光声光谱（FT-IR-PAS）的乙内酰脲环的波数，研究了每种晶型的分子堆积结构。从两种晶型的FT-IR-PAS数据可以清楚地看出，α型晶体中的氢键比β型晶体中的氢键更强。多晶型晶体系统的内聚力主要归因于氢键和范德华力。基于1的多晶型现象，明确了热力学稳定性取决于氢键模式，而熔化焓则源于范德华力。
