Glucose Mutarotation

This guided animation demonstrates how conformational flexibility enables interconversion between α and β anomers of a cyclic sugar through ring-chain tautomerism. In solution, these cyclic isomers are in equilibrium with each other as well as with the open chain form.

1. Starting with open-chain D-glucose in an extended conformation (drawn as a Fischer projection), bond rotations bring the C5 hydroxyl group into position for nucleophilic attack on the aldehyde.
2. Intramolecular attack of the C5 OH on the carbonyl, followed by proton transfers, forms α-D-glucopyranose. The newly created anomeric OH group is in the axial position.
3. The process can reverse through proton transfers and ring opening, regenerating the open-chain form.
4. A simple bond rotation in the open chain exposes the opposite face of the aldehyde to attack. Subsequent ring closure and proton transfers yield β-D-glucopyranose with the anomeric OH in the equatorial position.