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Organic and Biological Chemistry 4.10 Triglycerides 1

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Organic and Biological Chemistry . 4.10 Triglycerides. Triglycerides. Fats and oils from plants and animals Tri-esters of propan-1,2,3-triol (glycerol) Three long straight chain carboxylic acids (fatty acids) form ester linkages with each glycerol molecule. Carboxylic acid. - PowerPoint PPT Presentation

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Page 1: Organic and Biological Chemistry

Organic and Biological Chemistry 4.10 Triglycerides

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Page 2: Organic and Biological Chemistry

TriglyceridesFats and oils from plants and animalsTri-esters of propan-1,2,3-triol (glycerol)Three long straight chain carboxylic acids

(fatty acids) form ester linkages with each glycerol molecule

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Page 3: Organic and Biological Chemistry

Triglycerides

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C

H

H

OH C

H

O

H

C

H

H

O H

C

H

H

OH C

H

O

H

C

H

H

O H

Propan-1,2,3-triol

R C

O

O

H

R C

O

O

H

Carboxylicacid

Page 4: Organic and Biological Chemistry

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Page 5: Organic and Biological Chemistry

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Page 6: Organic and Biological Chemistry

TriglyceridesFatty acids contain an even

number of carbon atoms (between 12 and 20). The carbon chain can be saturated or unsaturated.

If there is more than 1 double bond the molecule is referred to as polyunsaturated

Naturally occurring tri-esters of propan-1,2,3-triol generally will contain three different fatty acids

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Page 7: Organic and Biological Chemistry

Examples of Fatty Acids

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Page 8: Organic and Biological Chemistry

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Oleic Acid

Page 9: Organic and Biological Chemistry

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Olive Oil

Page 10: Organic and Biological Chemistry

Triglycerides

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Triglycerides can be hydrolysed to produce glycerol and three fatty acid molecules.

In biological organisms that can utilise triglycerides for energy this reaction is catalysed by lipase enzymes

In the laboratory concentrated acid or alkali combined with heating can be used to break down the triglyceride

Page 11: Organic and Biological Chemistry

TriglyceridesThe state of an edible fat or oil at room

temperature can be used to determine its source.

Edible fats are solids at 25oC and generally are obtained from land animals

Edible oils are liquids at 25oC and are obtained from plants or marine animals

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Page 12: Organic and Biological Chemistry

TriglyceridesMelting points of fats and oilsAs the length of the carbon chain increases

so does the tm increase, due to increased dispersion forces.

As the degree of unsaturation increases (i.e. number of C=C bonds increases) the tm

decreases. The molecules can’t pack together as closely and so don’t solidify

Fat contains a greater percentage of saturated fatty acids than unsaturated fatty acids and as a result it is solid at room temperature

Oils contain a greater percentage of unsaturated fatty acids and are liquids

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Page 13: Organic and Biological Chemistry

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Page 14: Organic and Biological Chemistry

Reactions of TriglyceridesThe degree of unsaturation of a

triglyceride can be determined by its reaction with bromine or iodine

C

H

H

C

H

H

C

H

H

C

H

H

+

Br Br

Br Br

C

H

H

Br C

H

H

Br

C

H

H

Br C

H

H

Br

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This is referred to as an Addition reaction

The orange colour of the bromine disappears as the reaction occurs. (The products are colourless)

To enable the bromine to mix with the triglyceride both the bromine and triglyceride are dissolved in a non polar solvent (cyclohexane)

Page 15: Organic and Biological Chemistry

Reactions of TriglyceridesBy titrating a standard solution of bromine

(burette) with a known volume of a standard solution of fat or oil the degree of unsaturation can be measured.

The greater the amount of bromine required the greater the degree of unsaturation.

The end point is indicated by the first permanent orange colour in the flask.

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Page 16: Organic and Biological Chemistry

Reactions of TriglyceridesIodine numberThe degree of unsaturation of a fat

or oil is often described in terms of the iodine number

The iodine number is the mass of iodine that reacts with 100g of the fat or oil

The greater the iodine number the greater the degree of unsaturation

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Olive oil Iodine Number =75–94 (virgin and refined)

Page 17: Organic and Biological Chemistry

Reactions of TriglyceridesLiquid oils can be converted to solid fats by

catalytic hydrogenationThe vegetable oil is heated with hydrogen gas

under pressure in the presence of a nickel catalyst. These conditions increase the rate of reaction.

Sufficient hydrogen is added to produce a product that is solid at room temperature

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C

H

H

C

H

H

C

H

H

C

H

H

+

H H

H H

Ni High PNi

Ni

High P

High P

C

H

H

H C

H

H

H

C

H

H

H C

H

H

H

Page 18: Organic and Biological Chemistry

Organic and Biological Chemistry

4.11 Carbohydrates

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Page 19: Organic and Biological Chemistry

CarbohydratesGeneral formula is usually CxH2yOy

This can often be written as Cx(H2O)y

Carbohydrates are polyhydroxyaldehydes or polyhydroxyketones or compounds that produce these when hydrolysed

Can be monosaccharides, disaccharides or polysaccharides depending on the number of simple sugars in the molecule

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Page 20: Organic and Biological Chemistry

MonosaccharidesMonomersGeneral formula CxH2xOx where x = 3 to 8Water soluble (Hydrogen bond with water)Simple sugars eg. Glucose, FructoseSolids at room temperatureSweet

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Page 21: Organic and Biological Chemistry

GlucoseC6H12O6

Can exist as a chain or ring structureThese structures are in equilibrium in

aqueous solution

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D-Glucose α-D-Glucose

Page 22: Organic and Biological Chemistry

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Page 23: Organic and Biological Chemistry

GlucoseIn the chain form the aldehyde can be

oxidised by Tollen's reagent forming the silver mirror and the carboxylate ion but there is no reaction with the ring form

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H O C

H

H

C

H

O

H

C

H

O

H

C

O

H

H

C

H

O

H

C

O

H

H O C

H

H

C

H

O

H

C

H

O

H

C

O

H

H

C

H

O

H

C

O

H

TollensTollens

Tollens

H O C

H

H

C

H

O

H

C

H

O

H

C

O

H

H

C

H

O

H

C

O

O–

H O C

H

H

C

H

O

H

C

H

O

H

C

O

H

H

C

H

O

H

C

O

O–

This reaction causes the equilibrium to favour the formation of the chain structure

Page 24: Organic and Biological Chemistry

DisaccharidesTwo monosaccharides per moleculeFormed by a condensation reaction

(eliminating water)Can be hydrolysed to form

monosaccharidesWater soluble compounds (Hydrogen bond

with water)

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Page 25: Organic and Biological Chemistry

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Sucrose

Lactose

Maltose

Page 26: Organic and Biological Chemistry

PolysaccharidesLarge polymers of monosaccharidesFormed by condensation reaction and

broken down to monosaccharides by hydrolysis

(C6H10O5)n +½nH2O ½nC12H22O11

polysaccharide disaccharideC12H22O11 + H2O 2C6H12O6

disaccharide monosaccharideOverall(C6H10O5)n + nH2O nC6H12O6

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Page 27: Organic and Biological Chemistry

PolysaccharidesInsoluble in water. Although hydrogen

bonding can occur the large molecular size prevents mixing with water

Will absorb water

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Page 28: Organic and Biological Chemistry

PolysaccharidesCelluloseStructural material in plantsMade up of approx. 3000 glucose unitsStraight chain polymer

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Page 29: Organic and Biological Chemistry

PolysaccharidesStarchMade up of amylose 250-2000 glucose

units in a straight chain and amylopectin which contains hundreds of thousands of glucose in a branched chain structure.

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Page 30: Organic and Biological Chemistry

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AmyloseAmylopectin

Page 31: Organic and Biological Chemistry

PolysaccharidesGlycogenStorage molecule for glucose in liver and

muscleBranched chain polymer

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