4.10 Triglycerides 1

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 2

Triglycerides 3 Propan-1,2,3-triol Carboxylic acid

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Triglycerides Fatty 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 6

Examples of Fatty Acids 7

8 Oleic Acid

9 Olive Oil

Triglycerides 10 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

Triglycerides The state of an edible fat or oil at room temperature can be used to determine its source. Edible fats are solids at 25 o C and generally are obtained from land animals Edible oils are liquids at 25 o C and are obtained from plants or marine animals 11

Triglycerides Melting points of fats and oils As the length of the carbon chain increases so does the t m increase, due to increased dispersion forces. As the degree of unsaturation increases (i.e. number of C=C bonds increases) the t m 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 12

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Reactions of Triglycerides The degree of unsaturation of a triglyceride can be determined by its reaction with bromine or iodine 14 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)

Reactions of Triglycerides By 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. 15

Reactions of Triglycerides Iodine number The 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 16 Olive oil Iodine Number =75–94 (virgin and refined)

Reactions of Triglycerides Liquid oils can be converted to solid fats by catalytic hydrogenation The 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 17

4.11 Carbohydrates 18

Carbohydrates General formula is usually C x H 2y O y This can often be written as C x (H 2 O) 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 19

Monosaccharides Monomers General formula C x H 2x O x where x = 3 to 8 Water soluble (Hydrogen bond with water) Simple sugars eg. Glucose, Fructose Solids at room temperature Sweet 20

Glucose C 6 H 12 O 6 Can exist as a chain or ring structure These structures are in equilibrium in aqueous solution 21 D-Glucose α -D-Glucose

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Glucose In 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 23 This reaction causes the equilibrium to favour the formation of the chain structure

Disaccharides Two monosaccharides per molecule Formed by a condensation reaction (eliminating water) Can be hydrolysed to form monosaccharides Water soluble compounds (Hydrogen bond with water) 24

25 Sucrose Lactose Maltose

Polysaccharides Large polymers of monosaccharides Formed by condensation reaction and broken down to monosaccharides by hydrolysis (C 6 H 10 O 5 ) n +½nH 2 O  ½nC 12 H 22 O 11 polysaccharide disaccharide C 12 H 22 O 11 + H 2 O  2C 6 H 12 O 6 disaccharide monosaccharide Overall (C 6 H 10 O 5 ) n + nH 2 O  nC 6 H 12 O 6 26

Polysaccharides Insoluble in water. Although hydrogen bonding can occur the large molecular size prevents mixing with water Will absorb water 27

Polysaccharides Cellulose Structural material in plants Made up of approx glucose units Straight chain polymer 28

Polysaccharides Starch Made up of amylose glucose units in a straight chain and amylopectin which contains hundreds of thousands of glucose in a branched chain structure. 29

30 Amylose Amylopectin

Polysaccharides Glycogen Storage molecule for glucose in liver and muscle Branched chain polymer 31