Metastable polymorphic form of isopropylbenzophenone derivative directly obtained by the solid-state photoreaction investigated by ab initiopowder X-ray diffraction analysis
作者:Kotaro Fujii、Hidehiro Uekusa、Michitaro Fukano、Hideko Koshima
DOI:10.1039/c0ce00500b
日期:——
The crystalline state of 2-(2,4,6-triisopropybenzoyl)((S)-1-phenylethyl)benzamide (1) is known to undergo a diastereospecific Norrish type II photocyclization under UV irradiation, giving a single photoproduct (R,S)-cyclobutenol (2). Its polycrystalline form (2A) has a different X-ray diffraction pattern from the known polymorph 2B, which is obtained from recrystallization of the photoproduct. Such a polymorphic phenomenon, which is the result of a solid-state photoreaction, is, in itself, highly interesting and the structure of the photoproduct 2A should directly lead to the photoreaction mechanism. Thus, the crystal structure of 2A has been directly determined from the powder X-ray diffraction data. Interestingly, the crystal packing has been retained during the photoreaction process and, although the powder X-ray diffraction pattern is significantly different, there are only minor structural changes. The comparison of the crystal structures of 1 and 2A reveals the photoreaction mechanism. The lattice energy calculations of the polymorphic forms of 2A and 2B reveals that 2A, which is obtained only by the solid-state photoreaction, is less stable than 2B, which is why it is not reformed on recrystallization.
已知 2-(2,4,6-三异丙基苯甲酰基)((S)-1-苯乙基)苯甲酰胺 (1) 的晶态在紫外线照射下会发生非对映特异性 Norrish II 型光环化,产生单一光产物 (R,S )-环丁烯醇(2)。其多晶型(2A)具有与已知多晶型2B不同的X射线衍射图,其是从光产物的重结晶获得的。这种固态光反应的结果的多晶型现象本身就非常有趣,光产物2A的结构应该直接导致光反应机制。因此,从粉末X射线衍射数据直接确定了2A的晶体结构。有趣的是,晶体堆积在光反应过程中得到保留,尽管粉末X射线衍射图显着不同,但仅存在微小的结构变化。 1和2A晶体结构的比较揭示了光反应机理。 2A和2B多晶型的晶格能量计算表明,仅通过固态光反应获得的2A的稳定性不如2B,这就是它在重结晶时不重新形成的原因。