Define mutarotation.

Mutarotation is the change in optical rotation of a sugar solution as the α and β anomer forms reach equilibrium.

In aqueous solution, many sugars like glucose and fructose can open their ring and reclose it, creating two forms called anomers. For D-glucose, the α and β forms differ at the anomeric carbon (C1). When pure α-D-glucose dissolves, its optical rotation starts high, then drifts to a constant value as some converts to β-D-glucose. The same happens in reverse. This time-dependent shift is mutarotation.

Essentials

• Cause: Interconversion through the open-chain aldehyde form.
• Result: Equilibrium mixture with a fixed specific rotation.
• Catalysis: Acids and bases speed up the process.

Why it matters

• Helps confirm ring structures of sugars and their stereochemistry.
• Affects sweetness, reactivity, and food processing behavior.
• Important in carbohydrate chemistry and biochemistry labs.

Polarimetry tracks the rotation change over time and gives kinetic data. The equilibrium ratio depends on temperature and solvent, with β-D-glucose usually favored in water due to chair stability.