Tendency of some substituents on a cyclohexane ring to prefer axial orientation
The α- and β-anomers of D-glucopyranose.
In organic chemistry, the anomeric effect or Edward-Lemieux effect (after J. T. Edward and Raymond Lemieux) is a stereoelectronic effect that describes the tendency of heteroatomic substituents adjacent to a heteroatom within a cyclohexane ring to prefer the axial orientation instead of the less-hindered equatorial orientation that would be expected from steric considerations.[1] This effect was originally observed in pyranose rings by J. T. Edward in 1955 when studying carbohydrate chemistry.
The term anomeric effect was introduced in 1958.[2] The name comes from the term used to designate the lowest-numbered ring carbon of a pyranose, the anomeric carbon. Isomers that differ only in the configuration at the anomeric carbon are called anomers. The anomers of D-glucopyranose are diastereomers, with the beta anomer having a hydroxyl (−OH) group pointing up equatorially, and the alpha anomer having that (−OH) group pointing down axially.
The anomeric effect can also be generalized to any cyclohexyl or linear system with the general formula C−Y−C−X, where Y is a heteroatom with one or more lone pairs, and X is an electronegative atom or group.[3] The magnitude of the anomeric effect is estimated at about 4-8 kJ/mol in the case of sugars, but is different for every molecule.
In the above case, the methoxy group −O−CH3) on the cyclohexane ring (top) prefers the equatorial position. However, in the tetrahydropyran ring (bottom), the methoxy group prefers the axial position. This is because in the cyclohexane ring, Y = carbon, which is not a heteroatom, so the anomeric effect is not observed and sterics dominates the observed substituent position. In the tetrahydropyran ring, Y = oxygen, which is a heteroatom, so the anomeric effect contributes and stabilizes the observed substituent position. In both cases, X = methoxy group.
The anomeric effect is most often observed when Y = oxygen, but can also be seen with other lone pair bearing heteroatoms in the ring, such as nitrogen, sulfur, and phosphorus.[4]
The exact method by which the anomeric effect causes stabilization is a point of controversy, and several hypotheses have been proposed to explain it.
^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (1996) "Anomeric Effect". doi:10.1351/goldbook.A00372
^Juaristi, E.; Cuevas, G. (1992). "Recent studies of the anomeric effect". Tetrahedron. 48 (24): 5019–5087. doi:10.1016/S0040-4020(01)90118-8.
^Bauerfeldt, Glauco F.; Cardozo, Thiago M.; Pereira, Márcio S.; da Silva, Clarissa O. (1 January 2013). "The anomeric effect: the dominance of exchange effects in closed-shell systems". Organic & Biomolecular Chemistry. 11 (2): 299–308. doi:10.1039/c2ob26818c. PMID 23172415.
^Kirby, Anthony J. (1983). The anomeric effect and related stereoelectronic effects at oxygen; with 24 tables. Berlin [u.a.]: Springer. ISBN 978-0-387-11684-6.
organic chemistry, the anomericeffect or Edward-Lemieux effect (after J. T. Edward and Raymond Lemieux) is a stereoelectronic effect that describes the tendency...
the anomeric centre and the anomeric reference atom, hence they are relative stereodescriptors. The anomeric centre in hemiacetals is the anomeric carbon...
through a process known as mutarotation. The anomericeffect more accurately called the endo-anomericeffect is the propensity for heteroatoms at C-1 to...
conformer, rather than the anti-diaxial conformer, in more polar solvents. Anomericeffect Floris Akkerman; Jürgen Buschmann; Dieter Lentz; Peter Luger; Eva Rödel...
Hyperconjugation can be used to explain phenomena such as the gauche effect and anomericeffect. Orbital symmetry is important when dealing with orbitals that...
this effect, which has great interest in carbohydrate chemistry, dimethoxymethane is often used for theoretical studies of the anomericeffect. Industrially...
The ratio would be α:β 11:89 if it were not for the influence of the anomericeffect. Mutarotation is considerably slower at temperatures close to 0 °C...
synthesis of sucrose. His contributions include the discovery of the anomericeffect and the development of general methodologies for the synthesis of saccharides...
C-glycosyl structures, they are typically more resistant to hydrolysis. When an anomeric center is involved in a glycosidic bond (as is common in nature) then one...
chemical phenomena, including the anomericeffect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of...
well-known interactions. These include important phenomena such as the anomericeffect and hyperconjugation. It is important to note that stereoelectronic...
breaking-off of carbohydrates from the glycoproteins.[citation needed] Anomericeffect Carbohydrate Carbohydrate conformation Disaccharide Glycosidic bond...
Cambridge, where he received his PhD in 1996 for investigations into the anomericeffect. Wothers has co-authored the first edition of the well-known and best-selling...
interaction and has been widely used to explain such phenomena as the anomericeffect. A common requirement of hyperconjugation is that the bonds donating...
intuitively useful. For example, the stereoelectronic requirement for the anomericeffect can be rationalized using equivalent lone pairs, since it is the overall...
1007/s008940050026. S2CID 93821090. Box VG (12 November 1998). "The anomericeffect of monosaccharides and their derivatives. Insights from the new QVBMM...
glycosyl units. The monosaccharides, in nature prefer ɑ-linkages due to anomericeffect, but the disaccharides with ɑ-linkages are non-reducing thus deactivating...
Arthur Lyon Bowley Edison effect – Thomas Edison Edman degradation – Pehr Victor Edman Edward–Lemieux effect (a.k.a. Anomericeffect) – John Thomas Edward...
most thermodynamically stable product will result which, owing to the anomericeffect, is usually the alpha anomer. Fischer–Speier esterification - a more...
ISSN 0033-4545. Reed, Alan E.; Schleyer, Paul v. R. (November 1988). "The anomericeffect with central atoms other than carbon. 2. Strong interactions between...
bonds in side-by-side positions (Edward-Lemieux, also known as the anomericeffect). He has experimentally investigated the mechanism of Wolff rearrangement...
The elongated C1-N1, and shortened C1-O1 bonds are explained with an anomericeffect resulting from the interaction of the oxygen lone pairs with the σ*C-N...
or top face. Since the α-glycoside product will be favoured by the anomericeffect, the α-glycoside usually predominates. Different protecting groups...
disaccharides like sucrose and trehalose have glycosidic bonds between their anomeric carbons and thus cannot convert to an open-chain form with an aldehyde...
cyclic form, the carbon atom containing the carbonyl oxygen, called the anomeric carbon, becomes a stereogenic center with two possible configurations:...
glycoside is any molecule in which a sugar group is bonded through its anomeric carbon to another group via a glycosidic bond. Glycosides can be linked...
D-aldohexose has the −OH of the anomeric carbon below the plane of the carbon atoms, while the β-isomer has the −OH of the anomeric carbon above the plane. Pyranoses...
Global Information
