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Enantiomer self-disproportionation is a process in stereochemistry describing the separation of a non-racemic mixture of enantiomers in an enantioenriched fraction and a more racemic fraction as a result of the formation of heterochiral or homochiral aggregates. This process is known to exist in achiral column chromatography.
Additional recommended knowledge
In 2006, Vadim A. Soloshonokintroduced the term Enantiomer self-disproportionation or self-disproportionation of enantiomers. He investigated achiral separations of several trifluoromethyl compounds.
By column chromatography on regular silica gel with a hexane / ethyl acetate eluent (5:1), a 66.6% ee sample of a trifluoromethyl substrate is separated into several fractions ranging from 8.1% ee for the first fraction collected to > 99.9% ee for the last fraction collected. A presence of a strong electronegative group in the substrate such as the trifluoromethyl group is a prerequisite. The effect disappears when a more polar eluent is selected. A possible explanation is offered. Compounds with large electronegative groups such as trifluoromethyl can form supramolecular associations or aggregates or clusters in which these groups are separated from each other as much as possible with minimized electrostatic repulsions. When these associations are stacks of alternating R and S molecules (as in syndiotactic polymers) this can be accomplished very efficiently. This association will form a racemic fraction of relatively high molecular weight eluting more slowly than the non-associating enantiopure fraction.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Enantiomer_self-disproportionation". A list of authors is available in Wikipedia.|