The crystal structure of para-methyl-l-phenylalanine at 230 K resembles that of the para-fluorinated analogue from the literature but is commensurately modulated with seven molecules in the asymmetric unit (Z′ = 7). At 100 K, the superstructure loses its modulation, leading to a unit cell with Z′ = 1, with clear disorder in the phenyl ring orientations. The methyl-substituent in para-methyl-l-phenylalanine has, in contrast to fluorine, no polar interactions with protons of neighboring molecules, which might allow for the well-defined modulation of the crystal structure at 230 K.

中文翻译：

---

对位取代的1-苯丙氨酸的多态性和调控

在230 K时，对甲基-1-苯丙氨酸的晶体结构类似于文献中的对氟类似物的晶体结构，但在不对称单元中相应地被7个分子调制（Z '= 7）。在100 K时，上层结构失去了调节，导致Z '= 1的晶胞在苯环取向上明显无序。与氟相反，对甲基-1-苯丙氨酸中的甲基取代基与相邻分子的质子无极性相互作用，这可能允许在230 K时对晶体结构进行明确定义的调节。