CARBOHYDRATESCARBOHYDRATES

Isomerism, Functions, Isomerism, Functions, Classification, Properties Classification, Properties

and Reactionsand Reactions

IsomerismIsomerism

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

Types of IsomerismTypes of Isomerism

A.A. Structural IsomersStructural Isomers 1. Skeletal or chain1. Skeletal or chain 2. Position isomers2. Position isomers 3. Functional isomers3. Functional isomersB.B. StereoisomersStereoisomers 1. Geometric or cis-trans isomerism1. Geometric or cis-trans isomerism 2. Optical isomers2. Optical isomers a. Enantiomers a. Enantiomers b. Diastereomersb. Diastereomers

Structural IsomersStructural Isomers

Skeletal or chainSkeletal or chain

H H H H H

H – C – C – C – C – C –H

H H H H H

CH3

CH3 – C – CH3

CH3

Position IsomersPosition Isomers

CHCH33 – CH – CH22 – CH – CH22Cl CHCl CH33 – CH – CH – CH – CH33

ClCl

1-chloropropane 2- 1-chloropropane 2- chloropropanechloropropane

Functional IsomersFunctional Isomers

CHCH33 – CH – CH22 – OH CH – OH CH33 – O – CH – O – CH33

ethyl alcohol dimethyl ethyl alcohol dimethyl etherether

StereoisomersStereoisomers

• Geometric or cis-trans isomerismGeometric or cis-trans isomerism

H – C – COOHH – C – COOH H – C – COOHH – C – COOH

HOOC – CH H – C – COOH HOOC – CH H – C – COOH

fumaric acid (trans) maleic acid (cis)fumaric acid (trans) maleic acid (cis)

MP = 302 MP = 302 ooC MP = 130 C MP = 130 ooCC

Insoluble in water soluble in waterInsoluble in water soluble in water

Optical isomersOptical isomers

• Enantiomers – are mirror images of each Enantiomers – are mirror images of each other and non superimposable. They other and non superimposable. They have the same melting point, boiling have the same melting point, boiling point and solubility. Enantiomers are point and solubility. Enantiomers are either dextro-rotatory or levorotatory. either dextro-rotatory or levorotatory.

d – if the OH of the penultimate C is at d – if the OH of the penultimate C is at the rightthe right

l – of the OH of the penultimate C is at l – of the OH of the penultimate C is at the leftthe left

Diastereomers are not Diastereomers are not mirror images of each mirror images of each

other. They have other. They have different MP, BP and different MP, BP and

solubilities.solubilities.

CH

C

C

C

C

CH2OH

O

H OH

OH H

H OH

H OH

CH

C

C

C

C

CH2OH

O

OH H

OH H

H OH

H OH

CH

C

C

C

C

CH2OH

O

H OH

H OH

H OH

H OH

CH

C

C

C

C

CH2 OH

O

OH H

OH H

OH H

H OH

CH

C

C

C

C

CH2OH

OH OH

OH H

H OH

HOH

Functions of Functions of CarbohydratesCarbohydrates

• Skeletal or structural functions – for Skeletal or structural functions – for example cellulose, the major structural example cellulose, the major structural component of plant cell walls; and component of plant cell walls; and peptidoglycans of bacterial cell wallspeptidoglycans of bacterial cell walls

• Storage, nutrient and reservoir of Storage, nutrient and reservoir of chemical energy, to be enlarged or chemical energy, to be enlarged or depleted as the organism needs – e.g. depleted as the organism needs – e.g. glycogen and starch which are glycogen and starch which are produced or consumed in line with the produced or consumed in line with the energy needs of the cell energy needs of the cell

ClassificationClassification1.1. According to the number of sugar unitsAccording to the number of sugar units Monosaccharides – simple sugars that could not Monosaccharides – simple sugars that could not

be hydrolyzed further into smaller units under be hydrolyzed further into smaller units under reasonably mild conditions. Ex. Glucosereasonably mild conditions. Ex. Glucose

Oligosaccharides – are hydrolyzable polymers of Oligosaccharides – are hydrolyzable polymers of monosaccharides containing 2-6 molecules of monosaccharides containing 2-6 molecules of simple sugars. Ex. Sucrosesimple sugars. Ex. Sucrose

Polysaccharides – very long chains or polymers of Polysaccharides – very long chains or polymers of monosaccharides which may be linear or monosaccharides which may be linear or branched in structure; usually tasteless and branched in structure; usually tasteless and water insolublewater insoluble

Homopolysaccharides – made up of only one Homopolysaccharides – made up of only one kind of monosaccharide. Ex. Starch and glycogenkind of monosaccharide. Ex. Starch and glycogen

Heteropolysaccharides – made up of 2 or more Heteropolysaccharides – made up of 2 or more different kinds of monosaccharides. Ex. different kinds of monosaccharides. Ex. Hyaluronic acidHyaluronic acid

2. According to functional groups2. According to functional groups

• Aldose contains the aldehyde groupAldose contains the aldehyde group• Ketose contains the ketose groupKetose contains the ketose group

3.3. According to the number of carbon According to the number of carbon atomsatoms

Triose contains 3 carbon atomsTriose contains 3 carbon atoms

Tetrose contains 4 carbon atomsTetrose contains 4 carbon atoms

Pentose contains 5 carbon atomsPentose contains 5 carbon atoms

Hexose contains 6 carbon atomsHexose contains 6 carbon atoms

List of monosaccharidesTrioses:

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

α-D-Glucopyranose (Haworth projection)

β-D-Glucopyranose(Haworth projection)

Linkages in Linkages in DisaccharidesDisaccharides

• Maltose – contains 2 glucose units Maltose – contains 2 glucose units linked at linked at αα-1,4-1,4

• Cellobiose – contains 2 glucose units Cellobiose – contains 2 glucose units linked at linked at ββ-1,3-1,3

• Isomaltose – contains 2 glucose units Isomaltose – contains 2 glucose units linked at linked at αα-1,6-1,6

• Lactose – has one glucose and one Lactose – has one glucose and one galactose galactose

• Sucrose – has one glucose and one Sucrose – has one glucose and one fructosefructose

Linkages in Linkages in PolysaccharidesPolysaccharides

• Storage polysaccharidesStorage polysaccharides

Starch – the storage polysaccharide of Starch – the storage polysaccharide of higher plants; consists of 2 fractions: higher plants; consists of 2 fractions: amylose and amylopectinamylose and amylopectin

Glycogen – structure is similar to Glycogen – structure is similar to amylopectin but more highly branchedamylopectin but more highly branched

• Nutrient polysaccharides – ex. Inulin, Nutrient polysaccharides – ex. Inulin, found in bulbs of many plants, consists found in bulbs of many plants, consists of fructofuranose unit joined together of fructofuranose unit joined together by glycosidic linkageby glycosidic linkage

•Structural PolysacchridesStructural PolysacchridesCellulose – consists of d glucose Cellulose – consists of d glucose units; it is found in cell walls of units; it is found in cell walls of plants.plants.Pectins – contain arabinose, Pectins – contain arabinose, galactose and galacturonic acidgalactose and galacturonic acidhemicelluloses – are not cellulose hemicelluloses – are not cellulose derivatives; a homopolymer of d-derivatives; a homopolymer of d-xylosexylosechitin – a homopolymer of N-acetyl chitin – a homopolymer of N-acetyl D glucosamine; found in the shell D glucosamine; found in the shell of crustaceans and scales of of crustaceans and scales of insectsinsects