Formation and Structure of Glucose

Overview

• Glucose is a 6-carbon carbohydrate.
• Exists in two forms: linear and cyclic.
• Carbons are numbered officially: carbon 1, carbon 2, etc.

Conversion from Linear to Cyclic Form

1. Carbon 1 and Carbon 5 identified – important for conversion.
2. Intramolecular Reaction: Nucleophilic Attack
   • Hydroxyl (OH) group on Carbon 5 acts as a nucleophile.
   • Carbon 1 acts as an electrophile (aldehyde carbon).
   • Hydroxyl on Carbon 5 attacks Carbon 1.
3. Bond Formation
   • Nucleophilic attack forms a bond.
   • Pi electrons are pushed to oxygen on Carbon 1.
   • Molecule forms a specific conformation to enable reaction.
4. Cyclic Structure Formation
   • Oxygen anion gets protonated.
   • Cyclic form of glucose is formed.
   • Carbon 1 is now known as the anomeric carbon.

Anomers of Glucose

• Alpha (α) Anomer: Hydroxyl group points away from Carbon 6.
• Beta (β) Anomer: Hydroxyl group points in the same direction as Carbon 6.
• Remember:
  • If OH points away from Carbon 6 → α-anomer
  • If OH points towards Carbon 6 → β-anomer

Reversibility and Mutarotation

• Cyclic forms can revert to linear form.
• Mechanism (focus on α-anomer example):
  1. Protonation of oxygen in the cyclic form.
  2. Electrons form double bond, break existing bond, revert to linear structure.
• Process is reversible: linear → α-anomer → linear → β-anomer, etc.
• Mutarotation: Reversible process of conversion between linear and cyclic forms.