C. Mutarotation
- Mutarotation refers to the change in optical rotation when an aqueous sugar solution is allowed to stand.Sugars having potential free aldehyde or keto group exhibit mutarotation. Many sugars exist in two crystalline forms. For example, when D-glucose is dissolved in water and allowed to crystallize out by evaporation of water, one form of D-glucose is obtained If D-glucose is crystallized from acetic acid or pyridine, another form of D-glucose is obtained. These two forms exhibit different physical and chemical properties.
- A freshly prepared aqueous solution of α-D glucose has a specific rotation of +113o. If the solution of α- D-glucose is allowed to stand, the specific rotation changes to +52.2o.Similarly, a fresh solution of ß- D-glucose has a specific rotation of +19o which changes to +52.2o on standing.This change in optical rotation is called mutarotation. On standing in solution, the hemiacetal ring opens and reformed to give a mixture of α - and ß-D-glucose having a specific rotation of +52.2o
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