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Issue 9, 2011
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Metastable polymorphic form of isopropylbenzophenone derivative directly obtained by the solid-state photoreaction investigated by ab initiopowder X-ray diffraction analysis

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Abstract

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.

Graphical abstract: Metastable polymorphic form of isopropylbenzophenone derivative directly obtained by the solid-state photoreaction investigated by ab initiopowder X-ray diffraction analysis

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Publication details

The article was received on 06 Aug 2010, accepted on 15 Nov 2010 and first published on 21 Dec 2010


Article type: Paper
DOI: 10.1039/C0CE00500B
Citation: CrystEngComm, 2011,13, 3197-3201
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    Metastable polymorphic form of isopropylbenzophenone derivative directly obtained by the solid-state photoreaction investigated by ab initiopowder X-ray diffraction analysis

    K. Fujii, H. Uekusa, M. Fukano and H. Koshima, CrystEngComm, 2011, 13, 3197
    DOI: 10.1039/C0CE00500B

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