Preferred Label : anomeric effect;
IUPAC definition : 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.;
Origin ID : A00372;
See also
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.
