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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Chiral molecular alloys: Patterson-search structure determination of (L)-carvone and (DL)-carvone from X-ray powder diffraction data at 218 K
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Chiral molecular alloys: Patterson-search structure determination of (L)-carvone and (DL)-carvone from X-ray powder diffraction data at 218 K

机译：手性分子合金：从218 K的X射线粉末衍射数据确定（L）-香芹酮和（DL）-香芹酮的Patterson搜索结构

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摘要

The crystal structures of pure L-carvone [(R)-(-)-2-methyl-5-(1-methylethenyl)-2-cyclohexen-1-one, C-10.- H14O] and the equimolar mixture DL-carvone (RS) have been determined by Patterson-search methods at low resolution from laboratory X-ray powder diffraction data (218 K). Crystal data: (L) a = 6.8576 (3), b = 6.8831 (5), c = 19.988(2) Angstrom, P2(1)2(1)2(1) space group, Z = 4; (DL) a = 6.9744 (3), b = 6.8094 (6), c = 20.038 (7) Angstrom, Pcmn space group, Z = 4. The L-carvone structure has been refined by the Rietveld method as a rigid body, allowing the rotation of the isopropenyl group (R-p = 0.030 and R-wp = 0.043). Although the structure of DL-carvone could be unambiguously established, the Rietveld refinement was not possible due to the existence of preferred orientation in the sample and the difficulty in modelling the disorder. The molecular packing is essentialy the same for both compounds and can be explained as a stacking of two different molecular layers in the [001] direction. In each layer the molecules are placed with their long axis perpendicular to the layer plane, in a head-to-tail manner. The great similarity between the molecular shapes of L and D enantiomers favours the positional disorder in DL-carvone. This result confirms the mixed crystal formation for the chiral carvone system as proposed in recent thermodynamic studies. The DL-carvone crystal must be considered as a pseudo-racemate, since both enantiomers are randomly distributed over all the lattice sites.
机译：纯L-香芹酮[（R）-（-）-2-甲基-5-（1-甲基乙烯基）-2-环己烯-1-酮，C-10.- H14O]和等摩尔混合物DL-的晶体结构香芹酮（RS）已通过Patterson搜索方法以低分辨率从实验室X射线粉末衍射数据（218 K）确定。晶体数据：（L）a = 6.8576（3），b = 6.8831（5），c = 19.988（2）埃，P2（1）2（1）2（1）空间群，Z = 4; （DL）a = 6.9744（3），b = 6.8094（6），c = 20.038（7）埃，Pcmn空间群，Z =4。L-香芹酮结构已通过Rietveld方法精制为刚体，允许异丙烯基旋转（Rp = 0.030和R-wp = 0.043）。尽管可以明确地确定DL-香芹酮的结构，但是由于样品中存在优选的取向并且难以建模该障碍，因此无法进行Rietveld提纯。两种化合物的分子堆积本质上是相同的，并且可以解释为在[001]方向上两个不同分子层的堆叠。在每一层中，分子以其从头到尾的方式使其长轴垂直于层平面放置。 L和D对映异构体的分子形状之间的极大相似性有助于DL-香芹酮中的位置混乱。该结果证实了最近热力学研究中提出的手性香芹酮体系的混合晶体形成。 DL-香芹酮晶体必须视为假外消旋体，因为两种对映异构体均随机分布在所有晶格位点上。

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