Mutarotation

In stereochemistry, mutarotation is the change in optical rotation of a chiral material in a solution due to a change in proportion of the two constituent anomers (i.e. the interconversion of their respective stereocenters) until equilibrium is reached.

Cyclic sugars show mutarotation as α and β anomeric forms interconvert.

Mutarotation was discovered by French chemist Augustin-Pierre Dubrunfaut in 1844, when he noticed that the specific rotation of aqueous sugar solution changes with time.

A solution or liquid sample of a pure α anomer will rotate plane polarised light by a different amount and/or in the opposite direction than the pure β anomer of that compound.

One can monitor the mutarotation process over time or determine the equilibrium mixture by observing the optical rotation and how it changes.