Properties of Carbohydrates and Isomerism

Properties of Carbohydrates

Structure

• Composed of carbon, hydrogen, and oxygen.
• Contains hydroxyl groups for hydrogen bonding with water.
• Includes at least one carbonyl group (aldehyde or ketone).

Chemical Reactions

• Undergo oxidation, reduction, and esterification.
• Monosaccharides are reducing sugars.

Optical Activity

• Asymmetric carbon atoms allow rotation of plane-polarized light.
• Can be dextrorotatory (right) or levorotatory (left).

Solubility

• Most carbohydrates are water-soluble.
• Can form crystals or insoluble crystalline aggregates.

Energy Source

• Primary source of energy (4 kcal/g).
• Many cells prefer glucose for energy.

Glycosidic Bonds

• Formed by elimination of water between two monosaccharides.

Classification

• Classified as monosaccharides, disaccharides, oligosaccharides, or polysaccharides.

Isomerism

Structural Isomerism

• Same molecular formula, different structural arrangements.
• Example: Glucose (aldose) vs. Fructose (ketose) (C₆H₁₂O₆).

Stereoisomerism

• Same structural formula, different spatial arrangements.
  • Enantiomers: Mirror images (e.g., D-Glucose and L-Glucose).
  • Diastereomers: Not mirror images (e.g., D-Glucose and D-Galactose).

Anomerism

• Specific stereoisomerism in cyclic monosaccharides.
• Example: α-D-Glucose and β-D-Glucose differ at the anomeric carbon.

Epimerism

• Isomers differ around a single carbon atom (not anomeric).
• Example: D-Glucose and D-Mannose differ around the second carbon.

Ring-Chain Isomerism

• Exists in open-chain (acyclic) and ring (cyclic) forms.
• Example: Glucose can be an open-chain aldehyde or cyclic hemiacetal (pyranose).