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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Photodimerization of the alpha '-polymorph of ortho-ethoxy-trans-cinnamic acid in the solid state. 1. Monitoring the reaction at 293 K
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Photodimerization of the alpha '-polymorph of ortho-ethoxy-trans-cinnamic acid in the solid state. 1. Monitoring the reaction at 293 K

机译：固态的邻乙氧基-肉桂酸的α'-多晶型的光二聚化。 1.监测293 K下的反应

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摘要

Structural changes that occur during the [2 + 2] photodimerization of the metastable alpha'-polymorph of ortho-ethoxy-trans-cinnamic acid at 293 K are presented here. Crystals of the alpha'-polymorph were first stabilized by exposing the a-polymorph to UV light for a short period of time at 343 K. The photodimerization reaction was then carried out at 293 K and observed in situ by single-crystal X-ray diffraction. The alpha'-polymorph contains three molecules in the asymmetric unit, labelled A, B and C, which are arranged to form two potential reaction sites. The intermolecular distance between the C=C bonds of molecules A and B (making up the AB site) is 3.6 Angstrom, and these were observed to undergo photodimerization at 293 K. The corresponding distance between centrosymmetrically related C=C bonds in the CC site (made up of C molecules) is 4.6 Angstrom, and these remain unreacted even after 60 h irradiation at 293 K. The crystal of the final product, which corresponds to a 66.7% conversion (only two out of three molecules in the asymmetric unit take part in the photodimerization reaction at 293 K), contains an ordered arrangement of the photodimer and unreacted monomer. The crystal retains many structural features of the original monomer crystal, including carboxylic acid hydrogen bonds and C-H...O interactions. Single-crystal X-ray diffraction was used to monitor changes in the unit-cell parameters, reacting molecules and molecular conformations as the reaction progressed. The conformation of the photodimer obtained from the solid-state reaction differs from that of the photodimer obtained by recrystallization from solution.
机译：此处显示了在293 K时，正乙氧基-肉桂酸的亚稳态α'-多晶型物的[2 + 2]光二聚化过程中发生的结构变化。首先将α-多晶型物在343 K的紫外线下短时间稳定，以稳定α'-多晶型物的晶体。然后在293 K下进行光二聚化反应，并通过单晶X射线现场观察衍射。 α'-多晶型物在不对称单元中包含三个标记为A，B和C的分子，它们被排列形成两个潜在的反应位点。分子A和B（组成AB位点）的C = C键之间的分子间距离为3.6埃，观察到它们在293 K处发生了光二聚作用。CC位点上的中心对称相关C = C键之间的对应距离（由C分子组成）为4.6埃，即使在293 K照射60小时后，它们仍未反应。最终产物的晶体相当于66.7％的转化率（不对称单元中只有三个分子中的两个吸收了在293 K的光二聚反应中的一部分）包含光二聚体和未反应单体的有序排列。该晶体保留了原始单体晶体的许多结构特征，包括羧酸氢键和C-H ... O相互作用。单晶X射线衍射用于监测反应过程中晶胞参数，反应分子和分子构象的变化。从固态反应获得的光二聚体的构象与从溶液中重结晶获得的光二聚体的构象不同。

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