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001-es BibID:	BIBFORM019250
Első szerző:	Bényei Attila (vegyész)
Cím:	Do Nitrogen atoms assist the formation of racemic conglomerates? / Bényei Attila
Dátum:	2011
Megjegyzések:	Racemic mixtures usually crystallize in centrosymmetric space group or in non-centrosymmetric space group having both enantiomer or their symmetry related parts in the asymmetric unit. In some cases the enantiomers form separate macroscopic crystals i.e. racemic conglomerates. This means formation of crystals with a lattice of one of the 65 space groups allowed for chiral molecules (Sohncke space groups) and Z'=1. Such a lattice also indicate spontaneous resolution of the racemic mixture into pure enantiomers. Formation of racemic twin crystals is also possible. Surprisingly, during our study of tert-amino effect[1] several compounds were found to crystallize as racemic conglomerate reproducibly, although they have been prepared by achiral route. Circular dicroism studies revealed, that while the bulk does not show Cotton effect optical rotation could be observed by choosing one single crystal in the solid state or in solution. In the case of 6,7,8,8a-tetrahydrodibenzo[e,g]pyrrolo[1,2-a]azocine-9,9(10H)-dicarbonitrile (Figure 1) not only resolution by shape chirality of the molecule occurred but resolution of a chiral carbon center was also observed. Single crystal X-ray diffraction studies of urotropine derivatives with quaternary nitrogen atom also indicated formation of racemic conglomerates. Here presence of heavy atom made it possible to determine the absolute configuration of the crystal studied. Search of the CSD (Ver. 5.32, November 2010 with updates February 2011) resulted 1054 hits for structures with Sohncke space groups and Z'=1. Among these hits true racemic conglomerates could be found. According to our results this phenomena is not so rare as considered generally and maybe overlooked in several cases. However, deeper understanding of formation of enantiopure or enriched crystals under achiral conditions will have far reaching consequences. The phenomena can be considered as an example for absolute asymmetric synthesis, too. Several structures with this surprising property, found in the last two years, will be presented. Each of them contained at least one tertiary or quaternary nitrogen atom. Detailed experimental studies are under way to exclude the resolution effect of traces of chiral contaminants and checking the reproducibility of crystallizations. Acknowledgement: The work/publication is supported by the TÁMOP 4.2.1/B-09/1/KONV-2010-0007 project. The project is co-financed by the European Union and the European Social Fund.
Tárgyszavak:	Természettudományok Kémiai tudományok előadáskivonat Molekulatudomány
Megjelenés:	XXII. Congress and General Assembly of the International Union of Crystallography / ed. International Union of Crystallography. - p. 783
Pályázati támogatás:	TÁMOP-4.2.1/B-09/1/KONV-2010-0007 TÁMOP Szerkezet- és polimorfizmus kutatás
Internet cím:	Intézményi repozitóriumban (DEA) tárolt változat
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