Question

What is the difference between \(\alpha\) -glucose and \(\beta\) -glucose? Show the condensation of two glucose molecules to form a disaccharide with an \(\alpha\) linkage; with a \(\beta\) linkage.

Short answer

The key difference between α-glucose and β-glucose is the position of the hydroxyl group (-OH) on carbon 1 (C1). In α-glucose, it is below the ring plane, while in β-glucose, it is above. An α-glycosidic linkage forms between the C1 carbon of one α-glucose molecule and the C4 carbon of another, with the bond below the ring plane, creating maltose. A β-glycosidic linkage forms between the C1 carbon of one β-glucose molecule and the C4 carbon of another, with the bond above the ring plane, creating cellobiose.

Step-by-step solution

Understand the difference between α-glucose and β-glucose

α and β-glucose are isomers, which means they have the same molecular formula (C6H12O6) but a slightly different arrangement of atoms. The key difference between α and β-glucose is the position of the hydroxyl group (-OH) on carbon 1 (C1). In α-glucose, the hydroxyl group is below the plane of the ring. In β-glucose, the hydroxyl group is above the plane of the ring.

Formation of α and β Glycosidic Linkages

A glycosidic linkage is formed when two glucose molecules are joined together by a dehydration reaction (removal of water), resulting in a covalent bond called a glycosidic bond. For α-glycosidic linkage: An α-glycosidic bond forms between the α-glucose's C1 carbon (anomeric carbon) and the C4 carbon of another glucose molecule. In the linkage, the α-glucose's C1 hydroxyl group is below the plane of the ring, and the bond between the C1 and C4 forms below the plane of the ring. For β-glycosidic linkage: A β-glycosidic bond forms between the β-glucose's C1 carbon (anomeric carbon) and the C4 carbon of another glucose molecule. In the linkage, the β-glucose's C1 hydroxyl group is above the plane of the ring, and the bond between the C1 and C4 forms above the plane of the ring.

Demonstrate Condensation of Two Glucose Molecules for α and β Linkages

α-linkage: 1. Two α-glucose molecules come in close proximity, with their C1 and C4 hydroxyl groups facing each other. 2. The hydroxyl group on C1 of one α-glucose reacts with the hydroxyl group on C4 of another α-glucose molecule, releasing a water molecule (H2O). 3. The α-glycosidic bond forms below the plane of the ring between the C1 of one glucose molecule and the C4 of the other glucose molecule, creating a disaccharide called maltose. β-linkage: 1. Two β-glucose molecules come in close proximity, with their C1 and C4 hydroxyl groups facing each other. 2. The hydroxyl group on C1 of one β-glucose reacts with the hydroxyl group on C4 of another β-glucose molecule, releasing a water molecule (H2O). 3. The β-glycosidic bond forms above the plane of the ring between the C1 of one glucose molecule and the C4 of the other glucose molecule, creating a disaccharide called cellobiose.