mutarotation

Mutarotation is a phenomenon observed in carbohydrate chemistry where the optical rotation of a freshly prepared sugar solution changes over time until it reaches a stable value. This occurs because many sugars, like glucose and fructose, exist in solution not as linear molecules but as cyclic structures called hemiacetals or hemiketals.1

These cyclic forms are in equilibrium with the open-chain structure. Each form possesses a different optical rotation. The carbon atom involved in forming the ring is known as the anomeric carbon. Carbohydrate stereoisomers that differ only at this anomeric carbon are called anomers, specifically alpha and beta anomers, distinguished by the orientation of the hydroxyl group. This dynamic equilibrium between different stereoisomers is the cause of mutarotation.1