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Conformational Interconverion of Stilbene-type of Compounds in Crystals.

晶体中二苯乙烯类化合物的构象相互转化。

基本信息

批准号：
09640627
负责人：
OGAWA Keiichiro
金额：
$ 1.79万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640627/
关键词：
Crystals Stilbene Azobenzene Conformational interconversion X-ray crystallography スチルベン構造の乱れ

项目摘要

Although it has been known that molecules are in motion in crystals, most of them are samll amplitude thermal vibrations around equilibrium structures or rotational vibrations of whole molecules. Large amplitude intramolecular motions or conformational interconversions are rare. This study reveals that conformational interconversions by which molecular shapes change greatly take place in the crystals of certain compounds. For the crystals of stilbene-type compounds, an orientational disorder in which two molecules are approximately related to one another by 180ﾟrotation around their longest axes. Although the disorder has been studied repeatedly, it has remained unclear whether the disorder is dynamic or static. This study revealed on the basis of variable temperature X-ray crystallographic analyses that the disorder is dynamic. Thus, the disorder disappears with lowering the temperature. The disorder is accounted for by conformational interconversion during which a pedal motion occurs. The torsional vibration around the N-Ph bonds occurs so that two benzene rings remain parallel to each other and the orientation of the benzene rings to the crystalline lattice do not change. When the amplitude of the torsional vibration becomes much larger, a molecule with one of two orientations changes into the the conformer with the other conformation through the conformation in which the azo unit (C-N=N-C) is perpendicular to the benzene rings. The populations of the two conformers show a temperature dependence if two conformers have different stabilities in crystals. This phenomenon is of interest in relation to solid state properties and reactivities in organic crystals.

虽然人们已经知道晶体中分子是运动的，但大多数是围绕平衡结构的小振幅热振动或整个分子的转动振动。大幅度的分子内运动或构象相互转换是罕见的。本研究揭示了某些化合物的晶体中发生了使分子形状发生巨大变化的构象相互转换。二苯乙烯型化合物晶体的一种取向无序，其中两个分子围绕其最长轴旋转180度，彼此之间近似相关。虽然这种疾病已经被反复研究，但仍然不清楚这种疾病是动态的还是静态的。这项研究揭示了变温X射线晶体学分析的基础上，无序是动态的。因此，随着温度的降低，无序消失。这种紊乱是由构象相互转换引起的，在此过程中发生了踏板运动。在N-Ph键周围发生扭转振动，使得两个苯环保持彼此平行，并且苯环相对于晶格的取向不改变。当扭振振幅较大时，具有两种取向中的一种取向的分子，通过偶氮单元（C-N=N-C）垂直于苯环的构象转变为具有另一种取向的构象。如果两种构象异构体在晶体中的稳定性不同，则两种构象异构体的布居数具有温度依赖性。这种现象与有机晶体的固态性质和反应性有关。