Illustrated Glossary of Organic Chemistry

Anomeric effect: Originally defined as the tendency of heteroatomic substituents (such as an OH group) 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 alone. Now defined more broadly as the tendency of a molecular fragment X-C-C-Y (where X and Y are heteroatoms) to prefer a gauche conformation.

Equatorial cyclohexanol

Axial cyclohexanol
In cyclohexanol, the ratio of conformations is about 80:20 equatorial:axial.


In aqueous D-glucopyranose, the ratio of anomeric carbon configurations is about 36:64 β:α. This decreased preference for the equatorial position (compared to cyclohexanol) is due to the anomeric effect.