Absolute Configuration and Polymorphism of 2‑Phenylbutyramide and α‑Methyl-α-phenylsuccinimide

Crystal structures of racemic and homochiral forms of 2-phenylbutyramide (1) and 3-methyl-3-phenylpyrrolidine-2,5-dione (2) were investigated in detail by a single crystal X-ray diffraction study. Absolute configurations of the homochiral forms of 1 and 2, obtained by chromatographic separation of racemates, were determined. It was revealed that racemate and homochiral forms of 1 are very similar in terms of supramolecular organization (H-bonded ribbons) in crystal, infrared (IR) spectral characteristics, and melting points. The presence of two different molecular conformations in homochiral forms of 1 allowed mimicking of crystal packing of the H-bonded ribbons in racemate 1. Two polymorph modifications (monoclinic and orthorhombic) comprising very similar H-bonded zigzag-like chains were found for the homochiral forms of compound 2 that were significantly different in terms of crystal structure, IR spectra, and melting points from the racemic form of 2. Unlike compound 1, homochiral forms of compound 2 have a higher density than the corresponding racemate which contradicts the Wallach rule and indicates that, in this case, homochiral forms are more stable than racemate forms.本研究采用单晶X射线衍射（single crystal X-ray diffraction）技术，对2-苯基丁酰胺（1）与3-甲基-3-苯基吡咯烷-2,5-二酮（2）的外消旋体及同手性（homochiral）异构体的晶体结构进行了详细研究。通过色谱法分离外消旋体得到的化合物1与2的同手性异构体，其绝对构型已被确定。研究发现，化合物1的外消旋体与同手性异构体在晶体中超分子组装形式（氢键带状结构）、红外（IR）光谱特征以及熔点方面均极为相似。化合物1的同手性异构体中存在两种不同的分子构象，这使其可模拟外消旋体1的氢键带状结构的晶体堆积模式。化合物2的同手性异构体存在两种多晶型变体（单斜晶系与正交晶系），二者均包含结构高度相似的氢键锯齿状分子链；且这两种多晶型变体在晶体结构、红外光谱与熔点方面，均与化合物2的外消旋体存在显著差异。与化合物1不同，化合物2的同手性异构体的密度高于其对应外消旋体，这一结果与沃拉赫规则（Wallach rule）相悖，表明在此体系中同手性异构体的稳定性优于外消旋体。