Originally the thermodynamic preference for polar groups bonded to C-1 (the anomeric carbon of a glycopyranosyl derivative) to take up an @A00546@ position.
A00372-1.pngThis effect is now considered to be a special case of a general preference (the generalized anomeric effect) for @T06406@ (@G02593@) 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 @T06406@ @C01258@.
A00372-2.pngIn 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 (@E02094@-anomeric effect). The opposite preference is claimed for some systems, e.g., glycopyranosyltrialkylammonium salts, and has been referred to as the reverse anomeric effect.