| Abstrakt: |
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 2Ashould directly lead to the photoreaction mechanism. Thus, the crystal structure of 2Ahas 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 1and 2Areveals the photoreaction mechanism. The lattice energy calculations of the polymorphic forms of 2Aand 2Breveals 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. [ABSTRACT FROM AUTHOR] |
