1. Isomerism, Functions, Classification, Properties and Reactions
CARBOHYDRATES
Isomerism, Functions, Classification, Properties
and Reactions

2. Isomerism
The existence of two or more compounds with the same composition but different constitution.

3. Types of Isomerism Structural Isomers 1. Skeletal or chain
2. Position isomers
3. Functional isomers
Stereoisomers
1. Geometric or cis-trans isomerism
2. Optical isomers
a. Enantiomers
b. Diastereomers

4. Structural Isomers Skeletal or chain CH3 – C – CH3 CH3 H H H H H
H – C – C – C – C – C –H
H H H H H

5. Position Isomers CH3 – CH2 – CH2Cl CH3 – CH – CH3 Cl
1-chloropropane chloropropane

6. Functional Isomers CH3 – CH2 – OH CH3 – O – CH3
ethyl alcohol dimethyl ether

7. Stereoisomers Geometric or cis-trans isomerism
H – C – COOH H – C – COOH
HOOC – CH H – C – COOH
fumaric acid (trans) maleic acid (cis)
MP = 302 oC MP = 130 oC
Insoluble in water soluble in water

8. Optical isomers
Enantiomers – are mirror images of each other and non superimposable. They have the same melting point, boiling point and solubility. Enantiomers are either dextro-rotatory or levorotatory.
d – if the OH of the penultimate C is at the right
l – of the OH of the penultimate C is at the left

9. Diastereomers are not mirror images of each other
Diastereomers are not mirror images of each other. They have different MP, BP and solubilities.

11. Functions of Carbohydrates
Skeletal or structural functions – for example cellulose, the major structural component of plant cell walls; and peptidoglycans of bacterial cell walls
Storage, nutrient and reservoir of chemical energy, to be enlarged or depleted as the organism needs – e.g. glycogen and starch which are produced or consumed in line with the energy needs of the cell

12. Classification According to the number of sugar units
Monosaccharides – simple sugars that could not be hydrolyzed further into smaller units under reasonably mild conditions. Ex. Glucose
Oligosaccharides – are hydrolyzable polymers of monosaccharides containing 2-6 molecules of simple sugars. Ex. Sucrose
Polysaccharides – very long chains or polymers of monosaccharides which may be linear or branched in structure; usually tasteless and water insoluble
Homopolysaccharides – made up of only one kind of monosaccharide. Ex. Starch and glycogen
Heteropolysaccharides – made up of 2 or more different kinds of monosaccharides. Ex. Hyaluronic acid

13. 2. According to functional groups
Aldose contains the aldehyde group
Ketose contains the ketose group
According to the number of carbon atoms
Triose contains 3 carbon atoms
Tetrose contains 4 carbon atoms
Pentose contains 5 carbon atoms
Hexose contains 6 carbon atoms

14. Aldotriose: glyceraldehyde Ketotriose: dihydroxyacetone Tetroses:
List of monosaccharides
Trioses:
Aldotriose: glyceraldehyde
Ketotriose: dihydroxyacetone
Tetroses:
Aldotetrose: erythrose and threose
Ketotetrose: erythrulose
Pentoses:
Aldopentoses: arabinose, lyxose, ribose, deoxyribose, and xylose
Ketopentoses: ribulose and xylulose
Hexoses:
Aldohexoses: allose, altrose, galactose, glucose, gulose, idose, mannose and talose
Ketohexoses: fructose, psicose, sorbose and tagatose
Heptoses:
Keto-heptoses: mannoheptulose, sedoheptulose
Octoses: octolose, 2-keto-3-deoxy-manno-octonate
Nonoses: sialose

15. β-D-Glucopyranose
(Haworth projection)
α-D-Glucopyranose
(Haworth projection)

16. Linkages in Disaccharides
Maltose – contains 2 glucose units linked at α-1,4
Cellobiose – contains 2 glucose units linked at β-1,3
Isomaltose – contains 2 glucose units linked at α-1,6
Lactose – has one glucose and one galactose
Sucrose – has one glucose and one fructose

17. Linkages in Polysaccharides
Storage polysaccharides
Starch – the storage polysaccharide of higher plants; consists of 2 fractions: amylose and amylopectin
Glycogen – structure is similar to amylopectin but more highly branched
Nutrient polysaccharides – ex. Inulin, found in bulbs of many plants, consists of fructofuranose unit joined together by glycosidic linkage

18. Structural Polysacchrides Cellulose – consists of d glucose units; it is found in cell walls of plants. Pectins – contain arabinose, galactose and galacturonic acid hemicelluloses – are not cellulose derivatives; a homopolymer of d-xylose chitin – a homopolymer of N-acetyl D glucosamine; found in the shell of crustaceans and scales of insects