Question

Define mutarotation?

Answer 1

Mutarotation:

• Mutarotation is described as the change in the optical rotation due to the in equilibrium between the two anomers.
• Cyclic sugars show mutarotation as alpha and beta anomeric forms of interconnecting.
• Mutarotation is a difference in the specific rotation of plane-polarized light, due to the change in the equilibrium between two anomers in the solution.
• Mutarotation property was first observed in sugar.
• The specific rotation (optical rotation) of the aqueous solution relies on the optical rotation of both the anomers and their ratio in the aqueous solution.
  For carbohydrates to exhibit mutarotation, they must be hemiketal or hemiacetal.
• Usually, $\mathrm{\alpha },\mathrm{\beta }$ and monomers of carbohydrates are stable solids, but in the aqueous solution, they undergo an equilibrium process to give a mixture of two forms.

For example:
Mutarotation of lactose:

• Lactose is a disaccharide having an ordinary name milk sugar (reducing sugar), which comprises glucose molecule and galactose molecule linked by$\mathrm{\beta }(1\to 4)$-glycosidic linkage.
• Since lactose has beta acetal, it undergoes mutarotation at 20 °C and its equilibrium mixture comprises 37.3 % α-lactose (β-D-galactopyranosyl-(1→4)-α-D-glucopyranose) and $62.7\%\mathrm{\beta }-$lactose ($\mathrm{\beta }-\mathrm{D}-$galactopyranosyl$-(1\to 4)-\mathrm{\beta }-\mathrm{D}-$glucopyranose).