Enantiomer self-disproportionation is a process in

stereochemistry Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereois ...

describing the separation of a non-

racemic In chemistry, a racemic mixture, or racemate (), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates. ...

mixture of

enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

s in an enantioenriched

fraction A fraction (from la, fractus, "broken") represents a part of a whole or, more generally, any number of equal parts. When spoken in everyday English, a fraction describes how many parts of a certain size there are, for example, one-half, eight ...

and a more racemic fraction as a result of the formation of heterochiral or homochiral aggregates. This process is known to occur in achiral

column chromatography Column chromatography in chemistry is a chromatography method used to isolate a single chemical compound from a mixture. Chromatography is able to separate substances based on differential adsorption of compounds to the adsorbent; compounds move th ...

. The phenomenon was first reported in 1983 in the separation of an excess of

carbon-14 Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...

labeled (''S'')-(−)-

nicotine Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...

enantiomer and its isomer. Two fractions were recorded, one containing racemic nicotine and the other pure (''S'') enantiomer. In 2006, Vadim A. Soloshonok introduced 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 Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other l ...

with a

hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...

ethyl acetate Ethyl acetate ( systematically ethyl ethanoate, commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues ...

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 Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...

group in the substrate such as the trifluoromethyl group is a prerequisite. The effect disappears when a more

polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates * Polar climate, the c ...

eluent is selected. A possible explanation is offered. Compounds with large electronegative groups such as trifluoromethyl can form

supramolecular Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces, ...

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 Tacticity (from el, τακτικός, taktikos, "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. The practical significance of tacticity rests on the effects on the physical p ...

polymers) this can be accomplished very efficiently. This association will form a racemic fraction of relatively high

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

eluting more slowly than the non-associating enantiopure fraction.

References

# ''Unexpected phenomenon in the high-performance liquid chromatographic analysis of racemic 14C-labelled nicotine: Separation of enantiomers in a totally achiral system '' K. C. Cundy, P. A. Crooks, J. Chromatogr. 1983, 281, 17
Abstract
# {{Note, Soloshonok ''Remarkable Amplification of the Self-Disproportionation of Enantiomers on Achiral-Phase Chromatography Columns '' Vadim A. Soloshonok

Angewandte Chemie International Edition ''Angewandte Chemie'' (, meaning "Applied Chemistry") is a weekly peer-reviewed scientific journal that is published by Wiley-VCH on behalf of the German Chemical Society (Gesellschaft Deutscher Chemiker). Publishing formats include feature-length ...

Volume 45, Issue 5, Pages 766 - 769 2006''
Abstract
Stereochemistry

See also

References