Chapter 24.15, Problem 19P

Interpretation Introduction

Interpretation:

The structure of the key intermediate when $\text{maltose}$ undergoes mutarotation when dissolved in water is to be represented.

Concept introduction:

Disaccharides are carbohydrates that yield two monosaccharide molecules on hydrolysis.

Disaccharides are glycosides in which the alkoxy group attached to the anomeric carbon atom is derived from a second sugar molecule.

Maltose is made up from hydrolysis of starch.

In maltose, two $\text{D-glucopyranose}$ units are joined by a glycosidic bond between $\text{C-1}$ of one unit and $\text{C-4}$ of the other unit.

The linkage in maltose is called $\alpha \text{-glycoside}$. Alpha and beta designate the stereochemistry at the anomeric carbon.

The change from one anomeric form to the equilibrium mixture is accompanied by a change in optical rotation is termed as mutarotation.

Diasaccharides undergo mutarotation when dissolved in water.

The mutarotation is a slow process in aqueous solutions but can be catalyzed by either acid or base.

A base abstracts an acidic proton in the given structure.

The flow of electrons in the mechanism is shown by the curved arrows.

The open chain form of the sugar is the key intermediate in the mutarotation of disaccharides.