Chapter 25: Carbohydrates

The Anomeric Effect

• In substituted cyclohexanes we learnt that the substituents usually prefer the equatorial position due to steric effects (review ?)
• In rings containing O atoms and with adjacent electronegative substituents there is a preference for this substituent to be axial.

Do you need to review axial and equatorial terminology ?
• This is because of an electronic effect due to an interaction of the orbitals of the ring O and the substituent bond.
• The anomeric center is important to the reactivity of carbohydrates because it is the site at which ring opening occurs, becoming the carbonyl group, the important functional group.

Study Tip: The anomeric carbon or the anomeric center can be recognised by looking for the C that is attached to two O atoms by single bonds.

Compound	Line Drawing	3D Model
b-D-glucose

© Dr. Ian Hunt, Department of Chemistry, University of Calgary