Carbohydrates and Their Types

Carbohydrates

• Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen.
• They are categorized into monosaccharides, oligosaccharides, and polysaccharides.

Monosaccharides

• Simplest form of carbohydrates, also called simple sugars.
• General formula: Cn(H₂O)n
• Examples: glucose, fructose, galactose
• Building blocks of carbohydrates
• Cannot be broken down further by hydrolysis.

Oligosaccharides

• Formed by linking a few (2-10) monosaccharides.
• Examples: disaccharides like sucrose (table sugar) and lactose (milk sugar).

Polysaccharides

• Large molecules composed of many monosaccharide units.
• Examples: starch, cellulose, glycogen.

Stereoisomers

• Enantiomers: Mirror-image stereoisomers
  • D-glucose and L-glucose are enantiomers.
• Epimers: Sugars that differ in configuration at only one chiral center.
  • D-glucose and D-mannose are C-2 epimers.
  • D-glucose and D-galactose are C-4 epimers.

Cyclization and Anomers

• Monosaccharides with 5 or 6 carbon atoms often form ring structures.
• Cyclization occurs when a carbonyl group reacts with a hydroxyl group on the same molecule.
• This creates a new chiral center (anomeric carbon).
• The resulting ring structure exists in two forms: α-anomer and β-anomer.
• Hemiacetals and hemiketals are more stable than their corresponding open-chain forms.

Haworth Projections

• Two-dimensional representations of the cyclic forms of monosaccharides.

Mutarotation

• Interconversion of α and β anomers.

Chair Conformation of Glucose

• β-D-glucose is more stable than α-D-glucose.
• The equatorial position of the hydroxyl group on C1 in β-forms is more stable than the axial position in α.

Oxidation Reactions

• Oxidation reactions convert aldoses to lactones.
• Tollens' test example of an oxidation reaction.
• A cyclic ester linking the carboxyl group and a sugar alcohol is called a lactone.

Reduction Reactions

• Reduction reactions convert sugars to deoxy sugars or alditols.
• Deoxy sugars: a hydrogen atom replaces a hydroxyl group, examples include L-fucose and D-2-deoxyribose.
• Alditols: carbonyl group reduced to a hydroxyl group, examples include xylitol and sorbitol.

Sugar Esters, Phosphates, and Glycosides

• Sugar esters result from reacting alcohol with an acid.
• Sugar phosphates are sugar esters.
• Glycosides are formed when hemiacetals or hemiketals react with another alcohol
• Full acetals/ketals: complete replacement of both -OH groups with -OR groups.