https://doi.org/10.1351/goldbook.A00372
Originally the thermodynamic preference for polar groups bonded to C-1 (the anomeric carbon of a glycopyranosyl derivative) to take up an
axial
position.
This effect is now considered to be a special case of a general preference (the generalized anomeric effect) for
synclinal
(
gauche
) conformations about the bond C–Y in the system X–C–Y–C where X and Y are heteroatoms having nonbonding electron pairs, commonly at least one of which is nitrogen, oxygen or fluorine. For example in chloro(methoxy)methane the anomeric effect stabilizes the
synclinal
conformation
.
In alkyl glycopyranosides the anomeric effect operates at two sites (i) along the endocyclic C-1 oxygen bond (endo-anomeric effect) and (ii) along the exocyclic C-1 oxygen bond (
exo
-anomeric effect). The opposite preference is claimed for some systems, e.g., glycopyranosyltrialkylammonium salts, and has been referred to as the reverse anomeric effect.
Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2198 [Terms] [Paper]