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Unit 2 Nature’s Chemistry Organic Chemistry In this unit traditional organic chemistry is studied in the context of a wide range of everyday consumer goods. The chemistry of the important functional groups within these substances is emphasised, as are the characteristic chemical reactions. Unit 2 Nature’s Chemistry Organic Chemistry Prior Knowledge From previous work you should know and understand the following: 1. 2. 3. 4. 5. That molecular structure and physical properties of hydrocarbons are related. The names, molecular and structural formula of alkanes (C1-C8), alkenes (C2-C8) and cycloalkanes (C3-C8) straight and branched. How to identify isomers and draw their structural formulae. What is meant by saturated and unsaturated carbon compounds and how they can be distinguished. Addition reactions involving unsaturated hydrocarbons Unit 2 Nature’s Chemistry Organic Chemistry Prior Knowledge From previous work you should know and understand the following: 6. Alcohols functional group –OH and properties of alcohols 7. The names, molecular and structural formula of alcohols (C1C8), straight and branched. 8. Carboxylic acids functional group COOH and properties of carboxylic acids 9. The names, molecular and structural formula of carboxylic acids (C1-C8), straight and branched. Organic Chemistry Originally, chemical compounds were divided into 2 classes: Inorganic or Organic Organic compounds were derived from living things. It was believed that they contained a ‘vital force’ and could not be made from inorganic compounds (non-living sources). Organic chemistry is the study of carbon compounds Organic Chemistry Organic chemistry is basically the study of compounds containing carbon (with the exclusion of oxides and carbonates). There are so many compounds containing carbon that a whole branch of chemistry is devoted to their study. Organic molecules may be as simple as methane, CH4 or as complicated as cholesterol HO Revision from National 5 • • • • • Alkanes Alkenes Alcohols Carboxylic Acids Esters Homologous series A homologous series are a family of organic compounds with the same general formula. They have a common functional group. Examples of homologous groups include: Homologous series General formula Functional group Alkanes CnH2n + 2 Alkenes CnH2n C=C Alkynes CnH2n - 2 C=C Alkanols CnH2n + 1 OH R – OH Alkanoic acids CnH2n + 1 COOH R – COOH Alkanals CnH2n + 1 CHO R – CHO Alkanes and Alkenes Alkane general formula C n H 2n+2 Alkene general formula C n H 2n Structural formula H H H H C C C H H H H Straight Chain Name H H C H H H H C C C H H Meth Eth Prop But Pent Hex Hept Oct No C’s 1 2 3 4 5 6 7 8 Branched chains and unsaturated C=C bond CH3CH2CH3 CH3 (CH2)2CH3 CH3CH2CH2CH3 Condensed formula Molecular formula C4H9 Naming Compounds of Carbon Alkanes 1. 2. 3. 4. 5. Identify the longest chain Identify the ‘branches’ and name them. Number the carbon atoms on the longest chain, at the end giving the lowest numbers for the branches. Write the branches in alphabetical order. If there are more branches with the same name use di, tri etc Alkenes 1. 2. 3. 4. 5. Identify the longest chain, that contains a double bond. Identify the ‘branches’ and name them. Number the carbon atoms on the longest chain, starting from the end nearest the double bond. Pick the lowest number to describe the position of the double bond. Write the branches in alphabetical order. If there are more branches with the same name use di, tri etc Naming Organic Compounds, Alkanes H H H H H H H CH3 C C C C C C C H CH2 H H H CH2 H 1 CH3 H CH2 10 CH3 1. Decide on the type of compound (ie. consider functional group) 2. Select the longest chain. 3. Name the compound with the branched chains in alphabetical order. alkane 10 C’s decane 7-ethyl-3-methyldecane H H C2H5 H C C C 2 3 C = C H CH3 H H 1. Decide on the type of compound (ie. consider functional group) 1 CH3 H alkene 2. Select the longest chain 7 C’s heptene 3. Number the C atoms so that the functional group has the lowest number hept-2-ene 4. Name the compound with the branched chains in ascending order. 5,5-dimethylhept-2-ene H H CH3 H H H C C C C C H CH3 Cl H H 1. Decide on the type of compound (ie. consider functional group) 2. Select the longest chain H halogen (chloroalkane) 5 C’s pentane 3. Name the compound 3-chloro-2,2-dimethylpentane with the branched chains and halogen in alphabetical order. Structural Isomers There are two types 1. Chain isomerism. Here the isomers have different arrangements of carbon atoms or different chains. For example there are two compounds with the molecular formula C4H10 H H H H H C C C C H H H H butane H H H H H C C C H CH3 H H 2-methylpropane Here, you can see that 2-methylpropane has a side chain. 2. Position Isomerism. E.g Alkene isomers Here the isomers have the same carbon skeleton and functional group but the position of the functional group is different. H H H H H H H C C C H H Cl H 1-chloropropane H H H H C C C H H OH propan-1-ol H H C C C H Cl H H 2-chloropropane H H H H C C C H OH H propan-2-ol H CH3 CH CH2 CH3 propene CH3 CH CH3 CH CH3 CH C CH3 CH CH3 2,4-dimethy pent-2-ene But-2-ene CH3 CH2 CH C CH3 CH2 CH3 a) 3,3-dimethyl-1-pentene Naming Alkanols & Isomers • Just like the alkenes, the alkanols have isomers that are dependent on the position of the functional group, in this case the hydroxyl group (-OH). Example; and Draw and name the structure below! Now complete exercise 2.3 Move onto textbook – list some uses of alkanols. Uses of Alcohols • Drinks – the alcohol in beers and spirits is ethanol. • As a fuel – ethanol can be mixed with petrol (Gasohol) • Methylated spirits – industrial alcohol • As a solvent – in perfumes and cosmetics Carboxylic (Alkanoic) Acids Carboxylic acids, sometimes known as alkanoic acids, are a homologous group of organic acids which contain the carboxyl functional group: • The third member is; propanoic acid • What do you think the name of the first and second members are? Uses of Carboxylic Acids • Vinegar is a solution of ethanoic acid. • Ethanoic acid can also be used as a preservative in the food industry. • Carboxylic acids are used in household cleaning products including soap • In manufacture of important organic compounds), acetic anhydride (used in aspirins), cellulose acetate (used in synthetic fibres), various dyes, perfumes & medicines. • As a solvent it dissolves phosphorus, sulphur & iodine. • Carboxylic acids can be used to make chemicals called esters. Making an Ester Esters are made by reacting a carboxylic acid with an alcohol. This is known as esterification and is a CONDENSATION reaction. The name of the ester comes from the alcohol and carboxylic acid! Ethanoic Acid + Ethanol H O H H H-C - C HO-C-C-H OH H H H Ethyl ethanoate CH3COOC2H5 + Water H2O Key area: Esters, Fats and Oils Esters Overview In this section, learn about the characteristic chemistry and uses of esters, and find out how they are made by condensation reactions and broken down by hydrolysis. a) Esters Learning intention Learn how esters are named and identified and how to draw the structural formula of an ester. Esters Esterification, Alkanoic acids reacting with Alkanols. Alcohol + Carboxylic Acid Ester + Water H+ Esters have sweet smells and are more volatile than carboxylic acids. They are responsible for sweet fruit smells. 280 aromas make up a strawberry smell!! •3-methylbutyl ethanoate in bananas. •2-aminobenzoate is found in grapes. Uses of Esters • We imitate these smells by manufacturing flavourings. • Esters are also used in perfumes. • Esters can also be used as solvents in glues. • Polyesters are used to make plasticisers. • Methyl ester is a biodiesel. b) Making and naming Esters Learning intention Learn about how esters are formed by condensation reactions of carboxylic acids and alcohols. Making Esters One way of preparing esters is to condense an alcohol with a carboxylic acid: O O C R O alcohol H + H R' O carboxylic acid C R O R' + H2 O ester The reaction is slow at room temperature and the yield of ester is low. The rate can be increased by heating the reaction mixture and by using concentrated sulphuric acid as a catalyst. The presence of the concentrated sulphuric acid also increases the yield of ester. Making an Ester Esters are made by reacting a carboxylic acid with an alcohol. This is known as esterification and is a CONDENSATION reaction. The name of the ester comes from the alcohol and carboxylic acid! Ethanoic Acid + Ethanol H O H H H-C - C HO-C-C-H H H H Ethyl ethanoate CH3COOC2H5 + Water H2O Naming Esters R-yl R-OH + R’-COOH R’-COOR + Water First, the 1st word comes from the alcohol. The name ends in –yl. Second First O C2H5 C O C2H5 CH3 CH2 COO CH2 CH3 ethyl propanoate R’-oate Second, find the C=O in the carboxylate group, this gives the 2nd word with the ending –oate. This comes from the acid. Activity 1.1 Making Ester Experiment • The aim of this experiment is to prepare an ester and to identify some of the characteristic properties of esters. • Look at the next two slides Ester formation Condensation Reaction O R C O + O R H O R O C + R O H H Ester link H O R R C O CH3COOH + CH3OH ethanoic acid methanol CH3COOCH3 + H20 methyl ethanoate The reaction is brought about by heating a mixture of a carboxylic acid and an alcohol with a little concentrated sulphuric acid. (which acts as a catalyst and absorbs the water produced). Animation esterification Making esters Collect a workcard Procedure Decide which alcohol and carboxylic acid you need to make each ester in the table. 1. Before collecting the alcohol and carboxylic acid set up a water bath using the larger beaker and heat the water until it boils. Turn off the Bunsen. 2. Add the alcohol to a test tube to a depth of about 1 cm. To this add about the same volume of carboxylic acid. If the acid is a solid then use a spatulaful. 3.In the interests of safety your teacher/lecturer may carry out the next step. Add about 5 drops of concentrated sulphuric acid to the reaction mixture. Making esters 4. Soak the paper towel in cold water, fold it up and wrap it round the neck of the test tube. Secure it with a rubber band. This arrangement acts as a condenser when the reaction mixture is being heated. 5. Place a loose plug of cotton wool in the mouth of the test tube. This will contain any chemicals which may spurt out of the reaction mixture when it is heated. 6.Place the test tube in the hot water bath Making esters 7. While the reaction mixture is being heated add about 20 cm3 of sodium hydrogencarbonate solution to the small beaker. 8. After about 10 minutes, take the test tube from the water bath and remove the plug of cotton wool. Slowly pour the reaction mixture into the sodium hydrogencarbonate solution. This neutralises the sulphuric acid and any remaining carboxylic acid and so removes the smell of the carboxylic acid. 9. Gently swirl the contents of the beaker and look to see if there is any sign of the ester separating from the aqueous mixture. 10. To smell the ester with your nose at least 30 cm from the mouth of the beaker gently waft the vapour towards your nose and take just a sniff. 1.3 Uses of Esters Learning intention Learn about the many everyday uses of esters. Uses of esters Esters are oily liquids with generally very pleasant fruity smells and have a range of uses. Many esters are used as flavourings and in perfumes. Natural fruit flavours contain subtle blends of some of the esters in the table below: Esters are also used as non-polar industrial solvents. Name 3-methylbut-1-yl ethanoate Methyl Butanoate 3-Methylbutyl Butanoate Ethyl heptanoate 2-Methylpropyl methanoate Benzyl ethanoate Ethyl methanoate Methyl 2-aminobenzoate Benzyl butanoate Shortened Structural Formula Odour/Flavour CH3COOCH2CH2CH(CH3)CH3 Banana C2H5COOC4H9 Pear drops Pineapple C3H7COOCH2CH(CH3)C2H5 Apple CH3COOC3H7 Pear Grape, cherry Raspberry C3H7COOC5H11 Apricot, Strawberry CH3COOCH2C6H5 Peach, flowers C6H4(NH2)COOCH3 C3H7COOCH2C6H5 Grapes Cherry Uses of esters Factors affecting perfume design e.g. using esters: Designing a perfume - several issues to address by way of design factors. The perfume needs to be a mixture of compounds to give a prolonged perfumery effect. The perfumer chemist has to design the mixture to give a particular fragrance which includes ... the top note - the first fragrant molecule to be released, and the low note, the last molecule to be vapourised. Uses of esters Esters are also used as non-polar industrial solvents. Some of the smaller esters are quite volatile and are used as solvents in adhesives, inks and paints – pentyl ethanoate is used in nail varnish for example. Uses of esters Ethyl ethanoate is one of a number of solvents used to extract caffeine from coffee and tea. De-caffeinated products produced with ethyl ethanoate are often described on the packaging as "naturally decaffeinated" because ethyl ethanoate is a chemical found naturally in many fruits. Uses of esters Caffeine (C8H10N4O2) is an example of a class of compounds called alkaloids which are produced by plants. The name alkaloid means “alkali-like”, where alkali is a base and hence refers to these basic properties. Carryout the experiment to extract caffeine from tea. Uses of esters Caffeine is more soluble in the organic solvent ethyl ethanoate than in water, so we will extract caffeine into the organic solvent to separate it from glucose, tannins, and other water soluble compounds using a separating funnel. . The ethyl ethanoate portions can be combined and the ethyl ethanoate removed by evaporation to leave the caffeine http://www.periodicvideos.com/videos/mv_caffeine.htm 1.4 VOCs http://greencleaning.about.com/od/GreenCleaningResources /g/Volatile-Organic-Compounds-Vocs-What-They-Re-AllAbout.htm 1.5 Hydrolysis of Esters Learning intention Learn how esters can be broken down by hydrolysis into the parent carboxylic acid and alcohol. The process is the reverse of condensation – making esters. Process is called HYDROLYSIS Hydrolysing Esters Condensation Alcohol + Carboxylic Acid Ester + Water Hydrolysis Alcohol + Carboxylic Acid Ester + Water The ester is split up by the chemical action of water, hydrolysis. The hydrolysis and formation of an ester is a reversible reaction. O R C O R + H Bonds broken Ester + Water + O O H R C O O R H H Bonds formed Carboxylic Acid + Alcohol http://www.ltscotland.org.uk/highersciences/chemistr y/consumerchemistry/fruitflavours/makingesters.asp Examine some old perfume bottles What do you notice? Use all your senses Percentage Yield • You could be asked to calculate the mass produced if an experiment is working at x% efficiency or calculate the percentage yield. • Always follow the basic principles for all calculations • Start with a balanced chemical equation • Write down what you are told in the question • and what you are trying to work out. For percentage yield you need to know 2 things The actual yield in the experiment and the theoretical yield (from mole calculation). percentage yield = actual yield x 100 theoretical yield actual yield - usually given in question theoretical yield - Can be calculated from the equation Percentage yields CH3COOH + CH3CH2CH2OH <=> CH3COOCH2CH2CH3 + H2O 4.3 g of propyl ethanoate was produced when 6 g of ethanoic acid was reacted with propan-1-ol. What is the percentage yield of the ester? Percentage yield = actual yield/theoretical yield x 100% • Example • C6H6 + HNO3 -> C6H5NO2 + H2O • 18.72g of benzene, C6H6, enters a reaction chamber with excess nitric acid. After a time, 22.14g of nitrobenzene C6H5NO2 is obtained. • Calculate the percentage yield. 18.72g 78g Worked Answer xg 123g theoretical X g = 18.72 x 123 78 = 29.52g % yield = actual x 100 = 22.14 theoretical 29.52 = 75% • 2009 • 8. Ammonia is produced in industry by the Haber Process. • N2(g) + 3H2(g) --> 2NH3(g) • (c) Under certain conditions, 500 kg of nitrogen reacts with excess hydrogen to produce 405 kg of ammonia. • Calculate the percentage yield of ammonia under these conditions. • Show your working clearly. Worked Answer Fats and oils Overview In this section, study the chemistry and structure of edible fats and oils, and learn how the difference in melting points of fats and oils can be explained in terms of structural differences. 1.7 Edible fats and oils Learning intention Learn about the characteristic properties of fats and oils and study how they are formed by a condensation reaction of glycerol with fatty acids. Fats in our Diet We eat fats to provide us with energy. Fats provide more energy per gram than carbohydrates. Fat molecules are insoluble in water, and tend to group together and form a large droplet. This is how fat is stored in the adipose tissue. We store our extra energy as fat. Questions ; Are Fats/Oils polar or non-polar? What van der waal forces exist between fat molecules? The type of fat or oils we eat is important. Animal fats contain important fat soluble vitamins. Oils, are thought to be healthier than solid fats, as they are less likely to be deposited inside our arteries. However, there is an ongoing debate about which fats are better for us. Polyunsaturated fats are considered to be less potentially harmful to the heart. Origins of Fats and oils Naturally occuring Animal fat Vegetable oil Marine oil lard suet sunflower oil coconut oil cod liver oil whale oil Fats and Oils 50% of your brain is fat. Fats and oils are a range of substances all based on glycerol, propane-1,2,3-triol. Glycerol reacts with fatty acids to form a fat or oil molececule with ___ ester groups Natural fats and oils are a mixture of triglyceride compounds. H H C O H H C O H H C O H H Glycerol propane-1,2,3-triol An alcohol with three –OH groups Glycerol + 3 fatty acids = Fat/oil Each OH group in the glycerol can combine chemically with one carboxylic fatty acid molecule. The resulting molecules are fats and oils. Question: What is the name of this reaction? They are described as triglycerides. (tri esters) The hydrocarbon chain in each can be from 4 to 24 C’s long. The C’s can be single bonded (saturated) or double bonded (unsaturated). Fats and oils Fats and oils are ESTERS of glycerol and long chain carboxylic acids Fats and oils Fats and oils are built from an alcohol with three -O-H groups. glycerol Systematic name is propane-1,2,3-triol Fatty Acids – Saturated and Unsaturated C17H35COOH H3C CH2 CH2 C17H33COOH H3C CH2 CH2 CH2 Stearic Acid (suet, animal fat) Saturated CH3(CH2)16COOH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3(CH2)7CH=CH(CH2)7COOH CH2 CH2 CH2 CH2 CH Humans fatty acids Oleic acid 47% Palmitic acid 24% Linoleic acid 10% Stearic acid 8% CH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 O C OH Oleic Acid (olive oil) Unsaturated CH2 CH2 O C OH Octadec-9-enoic acid Fats and oils The other components of fat molecules are carboxylic acids such as Stearic acid Systematic name is octadecanoic acid In fats – the acid always has an even number of carbon atoms. Fats and oils Removal of water in the condensation reaction gives - The molecular formula shown above suggests that the fat molecule is shaped like an E, but the molecule is actually shaped more like this: b) The melting point of fats and oils Learning intention Learn how differences in structure of fats and oils lead to differences in strength of intermolecular forces, and therefore to differences in melting points. . Fats and oils Fats are mainly built from carboxylic fatty acids with C-C single bonds. They are said to be saturated and are linear (straight) in shape. Stearic acid in beef fat Oils have some C=C bonds in the carboxylic fatty acids from which they are made. They are said to be more Unsaturated and are not linear (straight in shape) Oleic acid in olive oil Fats and oils Oil Double bonds in oil make the molecule, slightly bent, not linear, so they are less compact. This means they are Less tightly packed molecules And their LDF are weaker, making oils liquid. Fat Fat molecules pack together more tightly due to their linear shape. So LDP forces are stronger, This makes fats solid at room temperature. Fat Oil Fat molecules pack together tightly, so stronger LDF, making fats solid at room temperature. Double bonds in oil make the molecule less compact. Less tightly packed molecules make oils liquid because the London Forces between molecules are weaker. Unsaturation in fats and oils 1. Using a plastic pipette, add five drops of olive oil to 5 cm3 of hexane in a conical flask. 2. Use a burette filled with a dilute solution of bromine water (0.02 moll–1) (Harmful and irritant). Read the burette. Scholar animation available Unsaturation in fats and oils 3. Run the bromine water slowly into the oil solution. Shake vigorously after each addition. The yellow colour of bromine disappears as bromine reacts with the oil. Continue adding bromine water to produce a permanent yellow colour. 4. Read the burette. Subtract to find the volume of bromine water needed in the titration. 5. Repeat the experiment with: five drops of cooking oil (vegetable) and five drops of cooking oil (animal). Fats and Oils The degree of saturation in a fat or oil can be determined by the Iodine Number. (bromine can also be used). The iodine reacts with the C=C bonds, so the greater the iodine number, the greater the number of double bonds. Fat Av Iodine No Butter 40 Beef Fat 45 Lard 50 Olive Oil 80 Peanut Oil 100 Soya Bean Oil 180 Solid fats – butter, beef fat & lard have low iodine numbers because they are more saturated than the unsaturated oils. Margarine is made from vegetable oils, butter from animal fats. One reason why margarine spreads better! Omega 3 fatty acids make up a large % of your brain’s fat. In practice both fats and oils are mixtures of esters containing both saturated and unsaturated compounds. Beef Fat Olive oil In general oils have a higher proportion of unsaturated molecules. Catalytic Hydrogenation of Oils (Hardening) The addition of hydrogen, using a nickel catalyst to an unsaturated oil will ‘harden’ the oil. The hydrogen is added across the double bond. It makes it more linear so will increase it’s m.p. So the oil becomes a solid! Question: Give another name for this porcess? This process is used to make margarine, otherwise margarine would be a liquid when taken out of the fridge. Yellow margarine song http://www.youtube.com/watch?v=7rzJNy_WZG4 Summary of the Chemistry of Fats and Oils http://www.educationscotland.gov.uk/highersci ences/chemistry/animations/oilsfats.asp Structures of Fats and Oils Hydrolysis of a fat or oil produces a molecule of glycerol (alcohol) for every 3 carboxylic acid molecules. The carboxylic acids are usually called long chain fatty acids. Most fats and oils are, in fact, esters of propane-1,2,3-triol, sometimes called, triesters. H O H C O C O R1 H C O C O R2 C R H C O 3 H Glycerol part Fatty acid part Triesters. R 1,R 2,R 3 are long carbon chains, which can be the same or different Hydrolysis Glycerol + Fatty Acids Key area: Proteins Overview In this section, study the structure and function of proteins. Learn about how they are formed from amino acids in condensation reactions, and how they are broken down by hydrolysis. a) Function of proteins Learning intention Learn about the function of proteins in living things. Proteins b) Making Protiens Amino Acids Learning intention Learn about the characteristic chemistry of amino acids, the building blocks of proteins. • Introduction to proteins An animation of three proteins which demonstrate common structural elements despite their very different functions. Amino acids All proteins contain the elements C,O,H, N. They are condensation polymers, made by amino acids linking together. Amino acids contain an Amine group -NH2 and an acid group -COOH Amino Acids H R O H N C C R O H NH2CHCOOH Most proteins contain 20+ different amino acids H When R is Hydrogen, the amino acid is glycine (Gly) (aminoethanoic acid) When R is CH3, the amino acid is alanine (Ala) (2-aminopropanoic acid) Amino acids c) Amide links Learning intention Learn how proteins are formed by condensation reactions of amino acids to produce amide (peptide) links. Protein Polymers and Essential Amino Acids Proteins are condensation polymers, made by amino acids linking together. An amine group of one molecule links to the carboxyl group of another molecule to form an amide link or peptide bond. Our body makes proteins by joining together amino acids in the right order to make the correct proteins. However, The body cannot make every type of amino acids that it needs. So our diet must contain essential amino acids. (about 10 of them). We synthesise the others. Protein Polymers CH3 H H O N–C-C OH H H + CH3 H O N–C-C OH H H + glycine alanine H N–C-C H O OH H alanine Tripeptide, ala-gly-ala CH3 O H H O H CH3 H O N–C– C - N–C–C- N–C-C OH H H H H Polypeptide chain can have 10000 amino acids amide (peptide) link + 2H2O Protein Structures Some proteins are composed of a single polypeptide chain, but many consist of two or more polypeptide chains. Proteins are classified according to their shape into fibrous and globular proteins. Fibrous proteins These have their polypeptide chains interwoven. The polypeptide chains are held together by hydrogen bonding, between the N-H and the C=O groups. This gives these proteins their properties of toughness, insolubility, and resistance to change in pH and temperature. So they are found in skin,tissue, (collagens), hair, nails (keratins). Globular proteins Proteins which operate within cells need to be soluble. The polypeptide chains are coiled together in spherical shapes. E.g. Haemoglobin and many hormones. e.g. Insulin, was the first protein structure to be worked out. Enzymes are globular proteins. Protein Structures Silk is a typical example of a fibrous protein. Silk This view shows the protein chains contain 2 different amino acids. This view shows the individual atoms in the protein chains. Protein Structures Albumin, in egg white, is a globular protein.. Albumin backbone view atom view Protein Structures Enzymes are globular proteins. The structure of amylase is shown below. Starch molecule in the enzyme’s active site. Enzyme Activity Enzymes catalyse chemical reactions in the body. Each enzyme has a unique shape held together by many weak bonds. Changes to pH and temperature can denature the enzyme. This changes the enzyme’s shape and stops it working properly. Narrow optimum range Enzyme activity Temp or pH The bonds that hold most biological enzymes are broken around 60oC. Enzyme Activity, Lock and Key The critical part of an enzyme molecule is called its active site. This is where binding of the substrate to enzyme occurs and where catalysis takes place. Most enzymes have one active site per molecule. Substrate Enzyme Scholar animation available Enzyme Activity, Lock and Key Substrate Enzyme Active site Enzyme Activity, Lock and Key The substrate becomes activated Enzyme Enzyme Activity, Lock and Key The substrate becomes activated Enzyme Enzyme Activity, Lock and Key The complex molecule splits Enzyme Enzyme Activity, Lock and Key The complex molecule splits Enzyme Practical Task • Factors Affecting Enzyme Activity • Collect a work card • Does temperature and pH effect enzymes? d) Hydrolysis of protein Learning intention Learn how proteins are broken down to amino acids by the process of hydrolysis. http://www.educationscotland.gov.uk/higherscience s/chemistry/animations/chemicalequations.asp This animation illustrates the process of protein formation by the condensation of the carboxylic acid and amine groups of amino acids. It also looks at the reverse process of protein hydrolysis Protein hydrolysis Proteins are broken down during digestion. Digestion involves the hydrolysis of proteins to form amino acids Protein + 2H2O Amino acids Chromatography Chromatography can be used to separate a mixture of different inks. Some example questions… R G B X 1) Ink X contains two different colours. What are they? 1 2 3 2) Which ink is ink Z made out of? Z Identifying amino acids by chromatography In the lab a protein can be hydrolysed back to its constituent amino acids by refluxing with concentrated hydrochloric acid for several hours. Amino acids can be identified by the use of paper (or thin layer) chromatography. A piece of chromatography paper is spotted with some amino acids suspected as being present and also with the hydrolysed protein. Identifying amino acids by chromatography By comparing the position of the spots of the known amino acids with that of the hydrolysed protein, the amino acids in the protein can be identified. •Add your results to the diagram •The hydrolysed fruit juice contained? Scholar animation available Key area: Chemistry of cooking Overview In this section, learn how functional groups in volatile molecules influence food flavour, and find out how cooking affects the structure of protein in food. a) Flavour in food Learning intention Learn how the chemistry of certain functional groups in volatile molecules in foods influence flavour. The chemistry of flavour The chemistry of flavour Molecules responsible for flavour in vegetables are normally trapped inside the cell walls. During cooking the cell walls are damaged for two reasons: • Chemical damage occurs as the cell walls, which are made of cellulose, break down. • Physical damage occurs as water inside the cells boils forming steam and the cell walls break open. The chemistry of flavour A major issue in cooking is to retain molecules responsible for flavour in the food – overcooking can result in loss of these molecules. One destination for lost flavour molecules is in the cooking water. This will occur if the flavour molecules are water-soluble. If this is the case, many of the flavour molecules will be lost down the drain when the cooking water is poured away. The chemistry of flavour • What is flavour? Illustrates the idea that flavour is taste plus aroma, and shows tasting experiments in which a blindfolded taster holds his nose and becomes unable to identify flavour. • Chocolat coulant Heston Blumenthal describes how to make a pudding containing chocolate and cheese and explains why this unlikely-sounding combination tastes good. • Fire and spice: the molecular basis for flavour Explains the stereochemical theory of odour which suggests that a molecule that fits into an olfactory receptor can fire nerve cells, ultimately producing a particular odour perception b) Flavour in foodChanges upon heating Learning intention Learn how heating proteincontaining foodstuffs leads to a change in food texture as intermolecular forces are broken. Changes in protein structure on heating • Within proteins, the long chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes. The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids. When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature).These changes alter the texture of foods. • Cooking meat Experiments in which different cuts of meat are cooked under different conditions to determine the optimum cooking temperature. Key area: Oxidation of foods Overview In this section, learn how oxidation reactions in foods convert alcohols to aldehydes and ketones, and study the role of antioxidants in the preservation of foods. . a) Oxidation of alcohols Learning intention In this section, learn about the products of oxidation of primary, secondary and tertiary alcohols. Find out about important mild oxidising agents and learn how to spot an oxidation reaction in a carbon compound. Classification of alcohols H H H C C H OH CH3 H H C CH3 H O H3C C CH3 H H H H C C C H OH H propan-2-ol H CH3 Secondary alcohol, One Hydrogen joined to the C bonded to the OH group Primary alcohol, Two Hydrogens joined to the C bonded to the OH group O Tertiary alcohol, No Hydrogens joined to the C bonded to the OH group CH3 H H3C C CH3 OH 2-methylpropan-2-ol Oxidation of Alcohols Primary alcohols can be oxidised by a number of oxidising agents, in two stages, 1st Stage - Hydrogen is lost; 2nd Stage - oxygen is gained. When applied to carbon compounds, oxidation results in an increase in the oxygen to hydrogen ratio. 1st H R C O oxidation H + O R O R C H + H2O aldehyde O H 2nd C H aldehyde + O oxidation O R C O H Carboxylic acid Secondary alcohols can be oxidised to form ketones, Tertiary alcohols do not undergo oxidation. O R C ketone R1 b) Aldehydes and Ketones Learning intention Learn about the characteristic functional groups and chemical reactions of aldehydes and ketones. Study how aldehydes and ketones are named and drawn. Aldehydes and Ketones Uses H + C=O Methanal, a 40% solution in water is formalin, and is used to make polymers (including Kevlar) C=O Ethanal, Its trimer (CH3CHO)3 is used as a sleep inducing drug. It also causes a hangover C=O Butanone, is a solvent used to make VHS tapes. H CH3 H CH3CH2 CH3 CH3 CH3 Butan-2-one C=O C4H8O Propanone, nail varnish remover and is used in the making of perspex Aldehydes and Ketones Distinguishing tests (Using mild oxidising agents.) Aldehydes are oxidised to carboxylic acids Ketones do not react with mild oxidising agents 1. Fehlings solution contains Cu2+ ions (blue) which form Cu+ ions (orange-red) in the presence of aldehydes. 2. Tollens’ reagent contains Ag+ ions, which form Ag in the presence of aldehydes (silver mirror test) 3. Acidified Potassium dichromate orange Cr2O72-(aq) to green Cr3(aq) Oxidation Collect a workcard Procedure 1. Before collecting the carbonyl compounds X and Y set up a water bath and heat the water until it boils. Turn off the Bunsen. 2. Add sulphuric acid to each of two test tubes to a depth of about 2 cm. Then add potassium dichromate solution to both to give a total depth of about 3 cm in each. 3. To one of these test tubes add about 5 drops of compound X and to the other add about 5 drops of compound Y. 4.Place both test tubes in the water bath and observe and record any changes. 5.Add Benedict's solution to each of two test tubes to a depth of about 3 cm. 6. Repeat steps 3 and 4. 7. Add Tollens' reagent to each of two very clean test tubes to a depth of about 3 cm. 8. Repeat steps 3 and 4 and immediately after, wash the contents of the test tubes down the drain with large amounts of water. Oxidation of Aldehydes and Ketones – What’s Happening? INTRODUCTION Both aldehydes and ketones contain the carbonyl group. C O In aldehydes a hydrogen atom is bonded to the carbonyl group but in ketones the carbonyl group is always flanked by carbon atoms: O C H aldehyde O C C C ketone This structural difference accounts for the fact that aldehydes can undergo mild oxidation to form carboxylic acids but ketones resist oxidation. Oxidising agents can therefore be used to distinguish between aldehydes and ketones. The aim of this experiment is to use the mild oxidising agents, acidified potassium dichromate solution, Benedict's solution and Tollens' reagent, to distinguish between two given carbonyl compounds one of which is an aldehyde and the other a ketone. Oxygen to Hydrogen Ratio • These are different definitions from those met previously and only apply in carbon chemistry. • oxidation • eg C2H5OH → CH3CHO • O:H 1:6 1:4 • • Oxidation of ethanol to ethanal has increased the O:H ratio. Ethanal can also be reduced back to ethanol and this would be a decrease of the ratio. • Try examples in your notes Oxidation of food • Oxidation reactions can occur when food is exposed to oxygen in the air. • Foods containing fats or oils are at the greatest risk of oxidation. • Antioxidants can help prevent oxidation Foods rich in fats and oils Oxidation of Fats Fats and oils, or foods containing them, are the most likely to have problems with oxidation. The oxidation of unsaturated oils and fats primarily takes place via a free-radical process where the C=C bond is attached by the free radical Fats react with oxygen and even if a food has a very low fat content it may still need the addition of an antioxidant to stop the free radical process. Fat Fat Oxygen http://www.understandingfoodadditives.org Effects of oxidation on food When fats react with oxygen they are broken down, causing: – deterioration of flavour (rancidity) due to production of aldehydes, ketones and carboxylic acids – loss of colour – loss of nutritional value – a health risk from toxic oxidation products. Antioxidants Added to Food Antioxidants are commonly used in: •vegetable oil •snacks (extruded) •animal fat •meat, fish, poultry •margarine •dairy products •mayonnaise / salad dressing •baked products •potato products (instant mashed potato) As the fat decomposes and reacts with oxygen, chemicals called peroxides are produced. These change into the substances characteristic of the smell and soapy flavour of a rancid fat. Antioxidants prevent the formation of peroxides and so slow the process of the food 'going off'. Some antioxidants react with oxygen itself and so prevent the formation of peroxides. Air-tight packaging, using inert gases like nitrogen, vacuum packing and refrigeration can all be used to delay the oxidation process. However, these can still be inefficient and adding antioxidants can be an effective way of extending the shelf life of a product. http://www.understandingfoodadditives.org Fat breaking down Fat Oxygen Fat molecules CH3 CH2 CH2 CH2 CH2 CH2 CH2 C O O H Fat O C H O C H C H H C CH2 CH2 CH2 O O CH2 C CH2 CH2 CH2 CH2 CH3 CH2 CH2 CH CH CH3 R CH2CH2CH2CH CH CH3 Radicals attack near the double bond (NB ‘R’ represents the remainder of the fat molecule) c) Antioxidants Learning intention Learn about the chemistry of the antioxidant molecules which prevent oxidation reactions in foods from taking place. Lesson Starter 1. There are many flavour and aroma compounds found in chocolate. Two examples are shown below. a. Which family of organic molecules does 1,3diphenylpropan-2-one belong to? b. Describe a test that could be used to distinguish between these two compounds. c. Draw the product made when phenylethanal undergoes oxidation. d. What is meant by oxidation? Antioxidants • Antioxidants are chemicals that are added to food to prevent the food from ‘going off’. • An antioxidant is a substance that slows down or prevents the oxidation of another chemical. • Anti oxidants can provide electrons to stop the loss of electrons (oxidation) from continuing! They are free radical scavengers (and reducing agents) Antioxidants Learning Intentions State what is meant by an antioxidant. Describe how antioxidants work. Give examples of common antioxidants. Antioxidants Antioxidants are molecules which prevent oxidation. This is important in the preservation of food as it spoils when it is oxidised. Vitamin C • Vitamin C is a powerful antioxidant. It is present in many fruits and vegetables. • Vitamin C is also known as ascorbic acid. Vitamin E • Vitamin E is a powerful antioxidant. • There are many sources of vitamin E... How do antioxidants work? • Antioxidants are compounds which will easily oxidise – they lose electrons. This means they oxidise in the place of the substance you are trying to protect (in this case the food). They give electrons to Free Radicals Vitamin C Oxidised Other uses for antioxidants • As well as their properties to prevent food spoilage antioxidants are believed to be beneficial to our health, in particular preventing ageing and a diet rich in antioxidants is thought to prevent forms of cancer. Antioxidants in action Oxidation occurs when the apple is left exposed to air The apple is protected when dipped in orange juice containing the antioxidant vitamin C Antioxidants Oxidation reactions happen when chemicals in the food are exposed to oxygen in the air. In natural conditions, animal and plant tissues contain their own antioxidants but in foods, these natural systems break down and oxidation is bound to follow. Oxidation of food is a destructive process, causing loss of nutritional value and changes in chemical composition. Oxidation of fats and oils leads to rancidity and, in fruits such as apples, it can result in the formation of compounds which discolour the fruit. Antioxidants are added to food to slow the rate of oxidation and, if used properly, they can extend the shelf life of the food in which they have been used. http://www.understandingfoodadditives.org Antioxidants and health benefits There may be health benefits from the use of antioxidants. Oxidation reactions in the body could be linked to the build-up of fatty deposits that cause blockages in arteries that can cause heart attacks. Antioxidants may be important in preventing this and there could also be a link with the prevention of certain cancers, arthritis and other conditions – antioxidant stop damage to our cells. The picture is not yet clear and a great deal of research needs to be undertaken. http://www.understandingfoodadditives.org Do antioxidants help us live longer? Studies involving 230,000 men and women across the UK have shown that there is no convincing proof that antioxidants have any effect on how long people can live. However 40% of women and 30% of men are reportedly taking these supplements and spending over £333 million on them per year. Impact of antioxidants on health Free radicals in living cells Free radicals are present in all living cell and are a part of the cell processes. However excessive free radicals in our cells can attack the cell membranes (the outer coat of the cell). This attack causes cell and tissue damage. Radicals can also break strands of DNA (the genetic material in the cell). Some of the chemicals known to cause cancer, do so by forming free radicals. The imbalance between free radicals and antioxidants can lead to disease and ill health. The 4 main non-enzymatic antioxidants metalonin, α-tocopherol (Vitamin E), ascorbic acid (Vitamin C) and βcarotene (precursor for Vitamin A) can be found in a range of foods in our diet. However medical opinions are divided as regards the impact these antioxidants have our on general health. Free Radicals and Oxidative damage – food (and skin) • Oxidation reactions can produce free radicals. • A free radical is a highly reactive species containing an unpaired electron. • Free radicals can damage food by removal of an electron. • Antioxidant molecules ‘mop up’ free radicals to protect the foodstuff. They are Free radical Scavengers Free Radicals and Antioxidants • • Free radicals are atoms or groups of atoms with an odd (unpaired) number of electrons and can be formed when oxygen interacts with certain molecules. Once formed these highly reactive radicals can start a chain reaction, like dominoes. Their chief danger comes from the damage they can do when they react with important cellular components such as DNA, or the cell membrane. Cells may function poorly or die if this occurs. To prevent free radical damage the body has a defense system of antioxidants. Antioxidants are molecules which can safely interact with free radicals and terminate the chain reaction before vital molecules are damaged. Although there are several enzyme systems within the body that scavenge free radicals, the principle micronutrient (vitamin) antioxidants are vitamin E, beta-carotene, and vitamin C. The body cannot manufacture these micronutrients so they must be supplied in the diet – i.e. fruits and veg as well as other foods. Radical now in a stable pair Damaging free radical Neutralised free radical Electron transferred Antioxidant Antioxidant converted to a stable free radical How does an antioxidant cancel out a free radical? The antioxidant molecule donates an electron to the potentially damaging free radical. A stable electron pair is formed, stabilising the free radical. The antioxidant itself becomes oxidised (loses an electron). Antioxidants are also Reducing Agents In a redox reaction, one reactant is oxidised (_________electrons) and the other is reduced (_________ electrons). E.g. Note: The electron donor is the _________ agent and the electron acceptor is the _________ agent. Antioxidants are _________ agents. They stop oxidation of food etc by __________ electrons to molecules. The table shows some typical antioxidants: http://www.understandingfoodadditives.org Antioxidant E-number Typical foods Ascorbic acid (vitamin C) E300 Beers, cut fruits, jams, dried potato. Helps to prevent cut and pulped foods from going brown by preventing oxidation reactions that cause the discolouration. Can be added to foods, such as potato, to replace vitamin C lost in processing. Tocopherols E306 Oils, meat pies. Obtained from soya beans and maize. Reduces oxidation of fatty acids and some vitamins. Butylated hydroxyanisole (BHA) E320 Oils, margarine, cheese, crisps. Helps to prevent the reactions that break down fats and cause the food to go rancid . Citric acid E330 Jam, tinned fruit, biscuits, alcoholic drinks, cheese, dried soup. Naturally-occuring in citrus fruits like lemons. Helps to increase the anti-oxidant effects of other substances. Helps to reduce the reactions that can discolour fruits. May also be used to regulate pH in jams and jellies. Vitamin C (ascorbic acid) • The antioxidant vitamin C can act as a reducing agent (electron donor), preventing oxidation (electron loss) from the foodstuff. C6H8O6 Ascorbic acid C6H6O6 + 2H+ + 2eDehydroascorbic acid Examples of Antioxidants Vitamin C - Ascorbic Acid Ascorbic acid is also known as Vitamin C and is commonly found in fruits and vegetables. It is one of the essential vitamins and the human body is unable to synthesize it. It can be easily oxidised and acts as a hydroxyl or superoxide anion radical scavenger. This is Vitamin C HO H HO HO O O OH This is Vitamin C acting as a Free radical Scavenger. R● is a free radical. The Vitamin C is oxidised and give a hydrogen to bond with the R●. It is now not a free radical. β-carotene This is a precursor to vitamin A. It is a highly red-orange pigment found in plants and fruits. In particular it gives carrots their orange colour. It helps human cells to absorb vitamin A. H3C H3C CH3 CH3 CH3 CH3 CH3 CH3 H3C CH3 Melatonin This is a hormone which helps to regulate sleep in our bodies. This compound can be termed as a terminal or suicidal antioxidant as once it has removed the free radicals it has to be replaced. H3C O HN HN CH3 O α-tocopherol This is a form of vitamin E and can be found in vegetable oil, nuts and seeds. It has been suggested that it is good for the skin. CH3 HO H H3C H CH3 CH3 CH3 O CH3 CH3 CH3 Practical Task The Assignment Investigating the levels of Antioxidants in different fruits and vegetables. Key Area: Soaps, Detergents and Emulsions Soaps,Detergents and Emulsions Overview In this section, learn about the chemistry of soap-making, find about how soaps and detergents clean, and study the chemistry of emulsions and emulsifiers. a) Making soap Learning intention Find out how soaps are formed by alkaline hydrolysis of fats and oils. Soaps Soaps are salts of fatty acids. Alkaline hydrolysis is used to make sodium salts of fatty acids Soaps are formed by the alkaline hydrolysis of fats and oils by sodium or potassium hydroxide by boiling under reflux conditions: . H H H H C C C O O O O C O H C H 17 35 C O C H C C H 17 35 17 35 H Glyceryl tristearate + 3NaOH H C O H H C O H H C O H H Glycerol + 3 C17H35COO -- Na + Sodium stearate (soap) http://www.educationscotland.gov.uk/hi ghersciences/chemistry/animations/s oapformation.asp This animation describes the formation of soap by the alkaline hydrolysis of fats / oils followed by neutralisation to form sodium salts of fatty acids. The structure of soap Hydrophobic tail COO- Na + Hydrophilic head The long covalent hydrocarbon chain gives rise to the hydrophobic (water hating) and oil-soluble (non-polar) properties of the soap molecule (represented in yellow). The charged carboxylate group (represented in blue) is attracted to water molecules (hydrophilic). In this way, soaps are composed of a hydrophilic head and a hydrophobic tail: Detergents Example of Detergent Structure Making Soap Practical b) Cleansing action of soap and detergents Learning intention Learn how the characteristic structure of soap and detergent molecules allows effective cleaning of oily stains to take place. Cleansing action of soaps The following ball (blue for hydrophilic head group) and stick (yellow for hydrophobic tail group) diagram represents the initial interaction of soap on addition to water and material with a grease stain: When the solution containing soap and water is agitated (stirred vigorously) the interactions of hydrophobicity and hydrophilicity become apparent. The hydrophobic, non-polar, tails burrow into the greasy, non-polar molecule – like attracting like. In the same way the polar hydrophilic head groups are attracted to polar water molecules. The head groups all point up into the water at the top of the grease stain. The attraction of the head group to the surrounding water, via polar-to-polar interactions, is so strong that it causes mechanical lift of the grease molecule away from the material on which it was deposited. The hydrophobic tails are anchored into the grease due to non-polar to non-polar attraction. In combination, these effects allow for the removal of the grease stain. http://www.educationscotland. gov.uk/highersciences/chemis try/animations/cleansingsoap.a sp Experiment • • • • • Collect 3 measuring cylinders Measure 50cm3 of distilled water 50 cm3 of soap solution Make up a 50% soap solution Add a spatula of MnO2 to each • Record observations • Explain the chemistry of what you see c) Emulsions in food Learning intention Learn about the characteristics of an emulsion, and study the chemistry of typical emulsifier molecules. Emulsifier molecules An emulsion contains small droplets of one liquid dispersed in an another liquid. Emulsions in food are mixtures of oil and water. To prevent oil and water components separating into layers, a soap-like molecule known as an emulsifier is added. Emulsifiers for use in food are commonly made by reacting edible oils with glycerol to form molecules in which either one or two fatty acid groups are linked to a glycerol backbone rather than the three normally found in edible oils. The one or two hydroxyl groups present in these molecules are hydrophilic whilst the fatty acid chains are hydrophobic. The presence of this emulsifier is shown on packaging by E-numbers, E471 and is one of the most common on food packaging. Emulsifiers Mayonnaise contains oil and water. The emulsifier keeps these mixed and without it the oil and water separate. Emulsifiers in food Emulsifiers in food Emulsifiers are among the most frequently used types of food additives. They are used for many reasons. Emulsifiers can help to make a food appealing. They are used to aid in the processing of foods and also to help maintain quality and freshness. In low fat spreads, emulsifiers can help to prevent the growth of moulds which would happen if the oil and fat separated. Emulsifiers in food Foods that Commonly Contain Emulsifiers Biscuits Toffees Bread Extruded snacks Chewing gum Margarine / low fat spreads Breakfast cereals Frozen desserts Coffee whiteners Cakes Ice-cream Topping powders Desserts / mousses Dried potato Peanut butter Soft drinks Chocolate coatings Caramels http://www.ltscotland.org.uk/higherscience s/chemistry/animations/emulsions.asp This animation explains the difference between a stable and an unstable emulsion, and goes on to show how addition of an emulsifier can stabilise an emulsion which is otherwise unstable. The chemical structure of a typical emulsifier is described and this is used to explain the favourable properties of emulsifiers Emulsifiers Practical Key area: Fragrances Overview In this section, learn about the chemistry of terpenes and essential oils, key components of fragrances. a) Essential oils Learning intention Learn about the constitution, properties and uses of essential oils. Essential oils • Essential oils are the concentrated extracts of volatile, non-water-soluble aroma compounds from plants. • Essential oils are widely used in perfumes, cosmetic products, cleaning products and as flavourings in foods. Essential oils • Essential oils are mixtures of organic compounds. • Terpenes are the key components in most essential oils. The history of essential oils • The benefits of essential oils have been recognised for thousands of years. • Their use is described in the New Testament of the Bible. • They were used in anointing rituals and in healing the sick. The history of essential oils The ancient Egyptians used essential oils for embalming, religious rites and medicinal purposes. King Tut’s tomb was found to contain 50 jars of essential oil when it was opened in 1922. Modern uses Cosmetics Dentistry Perfumes Cleaning Flavours Essential oils Adhesives Insect repellents Medical What are essential oils? • ‘Essential’ refers to the fact that the oil carries the distinctive essence (scent) of the plant. • Concentrated, volatile, non-water soluble aroma compounds extracted from plants. • Contain no artificial substances, unlike perfumes and fragrance oils. Essential oils – composition • Essential oils are mixtures of organic compounds. • Terpenes are the key components of all essential oils. Essential oils – chemistry • The distinctive character of an essential oil can be attributed to the functional group present in its key molecule. • Esters, aldehydes, ketones and alcohols are all found in essential oils. Essential oils – perfume • The ester linalyl acetate is found in the essential oil lavender. • This ester is often added to perfumes. H3C C CH3 O C H3C CH2 CH O CH3 C CH2 Linalyl acetate CH2 CH Essential oils – cleaning • The essential oil known as lemon oil contains the terpene d-limonene. • It is known for its ability to act as a natural solvent andCHa cleanser. H C 3 2 C CH H2C CH2 H2C CH C CH3 Limonene (skin of citrus fruits) Hospital Cleaners • Certain essential oils kill bacteria and fungi (including MRSA and E. coli) within 2 minutes of contact. • Essential oils are blended into soaps and shampoos used in hospitals to eradicate deadly ‘super bugs’. Essential oils – cosmetics • The essential oil geraniol is added to some cosmetics to balance and revitalise the skin. CH3 CH3 C H3C C CH2 CH CH2 Geraniol CH2 CH OH Essential oil – cold sores • Melissa oil contains the terpene citral, which is used to combat cold sores. CH3 C H3C CH CH2 CH2 Citral CH3 H C C CH O Essential oils – toothpaste • The essential oil thymol has antiseptic properties. CH3 C HC CH C CH HO C CH H3C Thymol CH3 Steam distillation • Steam distillation is one of the methods used to extract essential oils from plants. • Steam passes over the plant and extracts the essential oil. • The mixture evaporates and passes into the condenser. • The essential oil vapour is chilled and collected. Steam distillation Essential oils – summary • Concentrated extracts of volatile, non-watersoluble aroma compounds from plants. • Widely used in perfumes, cosmetics, cleaning products and flavourings. • Mixtures of organic compounds. • Terpenes are the key components of most essential oils. b) Terpenes Learning intention Learn about the chemistry and uses of terpenes, a key group of unsaturated molecules based upon isoprene. Terpenes • The name ‘terpene’ is derived from the Greek word ‘terebinth’. • Terebinth is a type of pine tree from which terpene-containing resins are obtained. What are terpenes? • Natural organic compounds. • Components of a variety of fruit and floral flavours and aromas. • Used in perfumes, essential oils and medicines. Essential oils contain terpenes • Lavender – used to relieve tension. • Ylang-ylang – used to treat anxiety. • Lemon oil – aids good circulation. • Essential oils often contain a mixture of terpenes. Spices contain terpenes • Terpenes in plants can be oxidised to produce the compounds responsible for the distinctive aroma of spices. • Terpenes containing oxygen or other functional groups are known as ‘terpenoids’. • Common spices containing terpenes include cloves, cinnamon and ginger. Terpenes are unsaturated • Terpenes are unsaturated compounds. • All terpenes are built up from units of isoprene. Isoprene • Isoprene is the common name for 2-methylbuta-1,3-diene CH3 H2C C H3C CH CH2 C CH2 H2C CH Isoprene Head Tail CH3 C CH2 CH = CH2 Isoprene (2-methylbuta-1,3-diene) One isoprene unit contains five carbon atoms Building terpenes from isoprene Isoprene units can be linked: • head to tail to form linear terpenes • in rings to form cyclic terpenes. Myrcene – a linear terpene Head CH2 H3C CH2 CHH23C H3C C H2C Head Tail C CH H3C C C CH Tail CH2 CH CH HH22CC • Myrcene is a component of plants, including bay, ylang-ylang and thyme. Limonene – a cyclic terpene CH2 H3C C CH H2C CH2 H2C CH C CH3 Limonene (skin of citrus fruits) Menthol – a cyclic terpenoid CH3 H3C CH CH OH H2C CH H2C CH2 CH CH3 Menthol (peppermint) This terpene has been oxidised to a terpenoid Absinthe – a cyclic terpenoid CH3 H3C This terpene has been oxidised to a terpenoid CH C H2C CH2 HC C CH CH3 Thujone (Absinthe) O Camphor – a cyclic terpenoid CH3 H3C C CH CH2 CH2 C H2C H3C C O Camphor (Camphor tree) a-Selinene – a cyclic terpene CH2 H2C H2C CH C 3 isoprene units CH3 CH2 C CH2 C CH2 CH2 C H CH3 -Selinene CH2 15 carbon atoms β-carotene – a linear terpene H3C H3C C C H2C C CH2 CH C CH H2C CH C CH2 C CH2 CH3 CH3 CH3 CH2 CH CH CH3 8 isoprene units 40 carbon atoms CH CH -carotene C CH3 CH CH CH CH CH C CH C CH3 C CH H3C CH3 Questions • Which unit makes up every terpene? • How many carbons are there in an isoprene unit? • What is the systematic name for isoprene? • What is an oxidised terpene known as? Answers • Which unit makes up every terpene? Isoprene unit • How many carbons there are in an isoprene unit? Five • What is the systematic name for isoprene? 2-methylbuta-1,3-diene • What is an oxidised terpene known as? Terpenoid Summary • Terpenes are unsaturated compounds formed by joining together isoprene units. • Terpenes are components in a wide variety of fruit and floral flavours and aromas. • Terpenes can be oxidised within plants to produce the compounds responsible for the distinctive aroma of spices. Key area: Skin care products Overview In this section, learn about the effect of UV-light on the skin, including the chemistry of freeradical reactions and the role of UV-scavengers in skin-care products. a) Effect of ultra-violet light Learning intention Learn how high energy UV-light causes damage to skin by breaking bonds in molecules. Sun, sea, sand and …. Ultraviolet radiation (UV) Image of the sun taken with ultraviolet imaging telescope • Ultraviolet radiation is broken into three types of wavelengths: • UV-A: This is the longest wavelength and is not absorbed by the ozone. It penetrates the skin deeper than UV-B. • UV-B: Responsible for sunburns. It is partially blocked by the ozone layer. • UV-C: This is totally absorbed by the earth's atmosphere; we encounter it only from artificial radiation sources. Ultraviolet radiation (UV) Ultraviolet radiation (UV) is a highenergy form of light, present in sunlight. Exposure to UV light can result in molecules gaining sufficient energy for bonds to be broken. UV damage to DNA Damage to DNA causes mutations which stop the DNA functioning properly The radiation excites DNA molecules in skin cells, causing new covalent bonds to form between adjacent cytosine bases, producing a bulge. This mutation can result in cancerous growths, and is known as is commonly seen in skin cancers. Skin cancer – malignant melanoma In the UK, 2,000 people a year die from malignant melanoma, and the number is increasing. Natural defence - Melanin Melanin is a pigment that is produced when your skin is exposed to sunlight. It absorbs the UV radiation found in sunlight to help protect your skin. This results in your skin becoming darker, a tan which is a sign that it has been damaged by UV rays. Melanin stops you burning so easily but it does not prevent the other harmful effects of UV radiation, such as cancer and premature ageing. Photo ageing • In the skin, UV radiation causes collagen to break down. • The body tries to rebuild the collegen, disorganized collagen fibers known as solar scars can form. • When the skin repeats this imperfect rebuilding process over and over wrinkles develop. There’s no such thing as a healthy tan Photoageing caused by UVA Exposed to sun (through car window) TAXI Driver Not exposed to sun The effects of UV - ageing of skin How to protect yourselfSunscreen • Sunscreen works by combining organic and inorganic active ingredients. • Inorganic ingredients like zinc oxide or titanium oxide reflect or scatter ultraviolet (UV) radiation. • Organic ingredients absorb UV radiation, dissipating it as heat. UV photography reveals sun damage This article illustrates how dermatologists use ultraviolet (UV) photography to show their patients how the sun has damaged the skin. Your health, your choices: Sunburn NHS information on sunburn, including symptoms, causes, treatment and prevention. Sunblock Guidance from the School of Medicine at the University of California, San Francisco, on the use of sunblock to prevent skin cancer. Lists common active ingredients of sunblock. UV Radiation and Children: A study of sunglass use to prevent ocular damage from sun exposure M. Bauer, W. Catanio, W. Fahrman, B. Godard, R. Irwin, A. Opyd New England College of Optometry, Boston, MA Purpose To determine if children are wearing sunglasses regularly. Results cont’d Conclusions cont’d Figure 2. The comparison of children and adult sunglass wear. Despite the public consciousness of UV damage there has been little public education involved in the prevention of cataracts, pterygia, or photokerititis. The most obvious and cost effective form of prevention is the use of sunglasses.4 Sunglasses are available in various styles and sizes, with 100% UV protection, at low cost. Comparative amount of sunglass use in children and parents Number of responses To investigate whether or not parents are aware of the harmful effects of UV radiation on young children's eyes. 160 140 120 100 80 60 parents children 40 20 0 Introduction Never Sometimes Always Amount Figure 3. Percent of children that wear sunglass in relation to parental use. Up to 80% of a lifetime sun exposure is obtained before the age 18. Children require special protection as they are at the highest risk for developing ocular damage or diseases caused by overexposure to Ultraviolet radiation from sunlight. It is important that parents teach their children how to enjoy fun in the sun safely. With the right precautions, the chance of developing ocular damage can be greatly reduced. It has been proven that simple measures, such as the use of brimmed hats and sunglasses, as personal protection measures can effectuate up to an 18-fold difference in ocular UV exposure.2 a. UV damage to cornea5 b. Pterygium5 d. Skin cancer6 c. Cataract5 Figure 1. Ocular disease manifestations. Methods A six-item survey was composed to access parental knowledge and awareness of the adverse effects of sunlight on the eyes. The surveys were handed out, with permission, at an elementary school and a pediatrician’s office in New Jersey and Rhode Island. Different states were surveyed in order to make the results generalizable throughout the United States. Results of the survey were analyzed in order to determine if public education would be beneficial to this issue. An educational pamphlet was made in order to inform the public on the negative effects of sunlight on the eyes. % of children that wear sunglasses Frequency of sunglass wear in children Acute eye damage can occur from single outings on bright days. Photokeratitis, (solar corneal damage) is a temporary but painful burn on the surface of the eye (cornea). This self-healing injury typically resolves in 24 hours with no permanent damage.1 Chronic UV exposure contributes to the development of many eye disorders: Pterygium is an abnormal growth of fibro-vascular tissue from the corner of the eye. If severe, a pterygium can grow over the cornea, threatening vision loss and requires surgery to be removed; Cataract is a clouding of the normally clear, natural lens inside the eye. The clouded lens prevents light from reaching the retina therefore reducing vision; Skin Cancer can develop on the eyelids and surrounding skin. Basal cell carcinomas, squamous cell carcinomas, and malignant melanomas can all occur from chronic UV exposure2,3 (Figure 1). The segment of the population at greatest risk to accrue damage from ultraviolet radiation is children from the ages of birth to adolescence. UV absorption by the natural lens of the eye varies throughout life. Immediately after birth, nearly all of the UV light is transmitted by the lens. During childhood, lens transmittance decreases, and by the age of 25, the lens absorbs UV light almost completely.2 Regardless of the fact that an overwhelming number of parents thought that childhood was the ideal age to start wearing sunglasses, only 11% answered that their children always wore sunglasses. Children’s lack of wearing sunglasses could be due to the fact that manufactures and advertisement companies are not using this age group as a demographic 120.0 5.8 100.0 5.6 18.8 80.0 60.0 38.9 65.3 Child Always Child Sometimes 56.3 Child Never 40.0 55.6 20.0 28.9 25.0 0.0 Parent Always Parent Sometimes Parent Never Parental sunglass use Figure 4. Parental awareness of ultraviolet radiation damage to the eye. UV damage awareness No 22% Yes realistic 28% Results Of the 800 surveys distributed, 235 were returned and analyzed. Parental educational background of those surveyed included college 57%, high school/GED 21%, graduate/masters 18%, and some high school 4%. When asked if they always, sometimes, or never wore sunglasses it was found that the majority of parents sometimes wore sunglasses. It was also found that the majority of their children sometimes wore sunglasses (Figure 2,3).When asked if their child would wear sunglasses if given a pair, 76% said yes. The majority of parents felt that childhood was the ideal age to start wearing sunglasses, with 75% of the responses. It was found that the majority of the people surveyed knew that UV radiation was damaging to the eyes (figure 4). Of these parents 50% were unable to provide a correct possible outcome. The top three incorrect answers were blindness, glaucoma, and sensitivity/squinting/soreness. The top three obtained correct answers were cataract, damage to retina, and damage to cornea. Yes false 50% Conclusions According to the results found in the previous section, 78% of adults surveyed were aware that ultraviolet radiation is damaging. However, half of them where unaware of the actual pathologies involved. The severity of sun exposure was also greatly underestimated. Common incorrect answers were blindness, glaucoma, watery eyes, and wrinkles. These general trends lead to several possible conclusions. One being that further education is a possible solution to the lack of adequate sunglass use. target. The most common answer of why children would not wear sunglasses was that they found them uncomfortable. More research on the design of children’s sunglasses could be beneficial to this issue. In conclusion, there is a serious lack of education on the damaging ocular effects of sun exposure. Moreover, there is little preventative behavior in preventing these potentially serious diseases. Because it is known that sunglass protection is most vital in childhood, it is alarming to see that a majority of youth are not protecting their eyes. This preliminary survey showed that there is a potential need for public health education on the adverse effect of UV radiation on the eye and the protection methods that could possible prevent these effects. A larger scale survey would be beneficial to determine nation wide parental knowledge on this subject. Future research would determine the most effective educational program. In order to aid the education process an ocular sun safety flyer will be distributed to optometric offices across the state of Massachusetts. References 1. Cronly-Dillon, J, Rosen, E. S., & Marshall, J. Hazards of light : myths & realities : eye and skin : proceedings of the First International Symposium of the Northern Eye Institute. University of Manchester, July 1985. 2. Friedlaender, Mitchell. Ultraviolet Radiation and the Eye. International Ophthalmology Clinics. 2005;45:49-52 3. Parisi, Alfio V., Green, A., & Kimlin, M. G. Diffuse Solar UV Radiation and Implications for Preventing Human Eye Damage. Photochemistry and Photobiology. 2000;73:135-139. 4. Van Kuijk J.G.M, Frederik. Effects of Ultraviolet Light on the Eye: Role of Protective Glasses. Environmental Health Perspectives. 1991;96:177-184 5. Ocular Image Database, New England College of Optometry Library [Internet]. [Cited 2006 Apr 26]. http://ncoimagesdb.ne-optometry.edu/ocular.asp. 6. Basal Cell Carcinoma (BCC), University of Utah John A. Moran Eye center [Internet]. [Cited 2006 Apr 26]. http://www.insight.med.utah.edu/opatharch/lid/basal_cell_carcinoma_bcc.htm. Acknowledgements A special thank you to Dr. Clifford Scott and Dr. Li Deng for their help with this public health project. b) Free radical reactions Learning intention Study the chemistry of free radical chain reactions. Hydrogen and chlorine When UV light breaks bonds free radicals are formed. Free radicals have unpaired electrons and, as a result, are highly reactive. Free radical chain reactions include the following steps: initiation, propagation and termination. Hydrogen and chlorine 1) Initiation U.V. light provides the energy for the homolytic fission of halogen into reactive halogen atoms or free radicals (atoms with an unpaired electron). Cl2(g) → Cl.(g) + .Cl(g) Hydrogen and chlorine 2) Propagation In this stage, free radicals collide with other species but the number of free radicals is maintained (hence the term propagation). H2(g) + .Cl → H.(g) + HCl(g) H.(g) + Cl2(g) → HCl(g) + Cl. (g) These reactions continue until reactants are used up, or until free radicals are used up by collision with each other. Hydrogen and chlorine 3) Termination In this stage, free radicals are used up by collision with each other. H.(g) + .Cl(g) → HCl(g) H.(g) + .H(g) → H2(g) Cl.(g) + .Cl(g) → Cl2(g) Free radical Substitution Methane Another free radical reaction takes place when halogen is substituted into an alkane in the presence of UV light. This reaction is not explosive and results in the decolourisation of bromine. Alkanes react with bromine in the presence of U.V. light, though the reaction with bromine is slow. The reaction can be shown as follows: CH4(g) + Br2(g) → CH3Br(g) + HBr(g) The presence of acid HBr in the product can be shown with moist pH paper. However, the reaction does not end here and further substitution can occur with hydrogen atoms progressively replaced by halogen atoms. The slow substitution reaction follows a free radical chain reaction, initiated by U.V. light (hν). For convenience, the reaction can be split into three stages. Free radical Substitution Methane 1) Initiation U.V. light provides the energy for the homolytic fission of halogen into reactive halogen atoms or free radicals (atoms or molecular fragments with an unpaired electron). Br2(g) → Br.(g) + .Br(g) Free radical Substitution Methane 2) Propagation In this stage, free radicals collide with other species but the number of free radicals is maintained (hence the term propagation). CH3-H(g) + .Br → CH3.(g) + HBr(g) CH3.(g) + Br2(g) → CH3 - Br(g) + Br. (g) These reactions continue until reactants are used up, or until free radicals are used up by collision with each other. Free radical Substitution Methane 3) Termination In this stage, free radicals are used up by collision with each other. Br.(g) + .Br(g) → Br2(g) CH3.(g) + .Br(g) → CH3 - Br(g) CH3.(g) + .CH3(g) → CH3 - CH3(g) The product of the last equation is ethane. However, to minimise the range of possible products, an excess of the original alkane is used and the products separated from the excess alkane by distillation. Free radical Substitution Methane Evidence to support this mechanism The reaction is initiated by U.V. light and, once started, can continue in the dark. Other substitution products are made such as CH2Br2, CHBr3, CBr4 together with longer alkanes (and smaller amounts of substitution products of these alkanes. However, these other substitution products can be minimised by using an excess of the original alkane to try to ensure collision of the relatively small number of free radicals produced by sunlight quickly uses up the bromine. c) Free-radical scavengers Learning intention Learn about the chemistry of the free-radical ‘scavenger’ molecules which are included in many skin-care products. Free Radical Scavengers Many cosmetic products contain free radical scavengers. These are molecules which can react with free radicals to form stable molecules and prevent chain reactions. Melatonin and Vitamin E are examples of natural free radical scavengers. Melatonin Free radical scavengers are also added to food products and to plastics. As UV light can cause wrinkling of skin, some skin-care products claim to contain chemicals which prevent wrinkling. These are claimed to be anti-aging creams. Free radicals remove electrons from skin cells and damage them and wrinkles start to develop. • Here is a banned advert. This time Nivea Visage is suggesting that the cream could deliver permanent benefits Do they work? • There is a range of antioxidants used in anti-wrinkle creams, and some are better at penetrating the skin than others. • The antioxidants used in skin care are derived from Vitamins A, E and C • The derivatives of Vitamins A (retinol) and E combat free radicals. Vitamin C is used in the construction of collagen. • Other antioxidants work by exfoliating the dead skin on the surface to reveal newer, younger-looking skin underneath. • Still others create a barrier to prevent moisture loss from the skin. • Claims for retinol derivatives say it can reduce the appearance of lines and reduce skin roughness, and blotchiness. There is some research that says retinol can increase the thickness of the epidermis. But as the molecules are large, they can't fit though the skin unless combined with substances that make the holes in the lipid matrix bigger. • Vitamin E is the most widely used ingredient in skin care products, used for its moisturising and antioxidant properties. Predicting Physical Properties of Molecules from Functional Groups Learning intentions To become familiar with identifying key functional groups within molecules. To be able to explain the influence of functional groups on intermolecular forces. To be able to predict the physical properties of molecules from functional groups present. Butanoic acid has a powerful, unpleasant odour. It is found in rancid butter, Parmesan cheese and vomit. Carboxyl group Can you identify and name the functional group present in butanoic acid? Aqueous solutions of methanal are commonly used in embalming to preserve human or animal remains. Carbonyl group Can you identify and name the functional group present in methanal? Is methanal an aldehyde or a ketone? Aldehyde The molecule below is found in the disinfectant Dettol, which we instantly recognise by its distinctive smell. Dettol (chloroxylenol) helps us fight unwanted bacteria. Hydroxyl group Can you identify and name the functional group present in Dettol? 4-formamidobenzoic acid is used in pharmaceutical compositions. Carboxyl group Amide group Can you identify and name two functional groups present on the 4-formamidobenzoic acid molecule? Cinnamon is a tasty spice used to flavour biscuits, cakes and pies. Cinnamon also has medicinal properties. Carbonyl group Carbon-tocarbon double bond Can you identify and name two functional groups in cinnamon? Is cinnamon an aldehyde or a ketone? Aldehyde What is the strongest type of intermolecular force of attraction between cinnamon molecules? (Hint: Think about the bond polarity of the functional groups present!) Methyl anthranilate occurs naturally in grapes and is used as grape flavouring in drinks and chewing gum. Ester link Amino group Can you identify and name the two functional groups present in methyl anthranilate? Vitamin C is needed in your diet for the growth and repair of tissues in all parts of your body. Ester link Carbon-tocarbon double bond Hydroxyl group Can you identify and name three different types of functional group on the structure of vitamin C? Which is the strongest type of intermolecular force of attraction between molecules of vitamin C? Is vitamin C a polar or a non-polar molecule? Is vitamin C soluble in water or in hexane? (Hint: Think about which functional groups are present!) Glucose is a simple sugar that is used as an energy source by many living organisms. Is glucose soluble in water or in hexane? Justify your answer with reference to the functional groups present. 2-methylpropane is a branched hydrocarbon that is used as a refrigerant. Is 2-methylpropane soluble in water or in hexane? Justify your answer with reference to the structure.