CBSE Class 12 Chemistry: Carbohydrate Classification and Structure
Question Analysis: Based on the provided text, classify the following as monosaccharides, disaccharides, or polysaccharides and explain the nature of the glycosidic linkage.
Step 1 (Definition & Classification): [1.5 Marks]
- Monosaccharides: Simplest sugars that cannot be hydrolyzed further (e.g., Glucose, Fructose).
- Disaccharides: Sugars that yield two molecules of monosaccharides on hydrolysis (e.g., Sucrose, Maltose).
- Polysaccharides: Complex carbohydrates that yield a large number of monosaccharide units on hydrolysis (e.g., Starch, Cellulose, Glycogen).
Step 2 (Mechanism of Glycosidic Bond Formation): [1.5 Marks]
The formation of a glycosidic bond is a condensation reaction where two monosaccharide units join by the elimination of a water molecule ($H_2O$). The general reaction can be represented as:
$$C_6H_{12}O_6 + C_6H_{12}O_6 \xrightarrow{\text{Condensation}} C_{12}H_{22}O_{11} + H_2O$$In this process, the hydroxyl ($-OH$) group of one monosaccharide reacts with the anomeric carbon of another, forming an ether linkage ($C-O-C$) known as the glycosidic bond.
Step 3 (Final Conclusion & Identification): [1.0 Mark]
Based on the provided text:
- Starch, Glycogen, and Cellulose: Classified as Polysaccharides.
- Reducing/Non-reducing nature: Depends on the presence of a free hemiacetal or hemiketal group. If the anomeric carbon is involved in the glycosidic bond (e.g., in Sucrose), it is a non-reducing sugar.
💡 EL10 Concept Insight: Think of monosaccharides like single LEGO bricks; a disaccharide is two bricks snapped together, and a polysaccharide is a massive, long tower of bricks. When you snap them together, you have to "click" them into place, which is like the glycosidic bond, and a tiny bit of water is squeezed out during that connection!