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Organic chemistry

Organic chemistry

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Organic chemistry

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  1. Organic chemistry IGCSE Chemistry 0620

  2. What are organic compounds? • Organic compounds are hydrocarbons and related compounds • Hydrocarbons are compounds made up of carbon and hydrogenonly. • Carbon atoms can join one to another to form carbon chain with different number of carbon atoms. Because of this there are huge number of organic compounds. • This property of carbon is called ‘catenation’.

  3. Saturated and unsaturated compounds • If all bonds between carbon atoms are single, the compounds are saturated compounds. • If a double or a triple bond is present between carbon atoms, the compounds are called unsaturated. • In saturated compounds, all valencies of carbon atoms are fully used up. So saturated compounds are not reactive.

  4. Single bond hydrocarbons are called ALKANES • Double bond hydrocarbons are called ALKENES • Triple bond hydrocarbons are called ALKYNES (You need to know only about alkanes and alkenes)

  5. Saturated Hydrocarbons

  6. Unsaturated compounds have one or more valencies in carbon atoms are free. • Second and third bonds are temporary. So if other atoms available, unsaturated compounds are very reactive.

  7. Alkenes

  8. Naming hydrocarbons • Each organic compound has two parts in their names: • Prefix depends on how many carbon atoms present. • 1 carbon compound Meth- • 2 carbon compound Eth- • 3 carbon compound Prop- • 4 carbon compound But- • 5 carbon compound pent- • 6 carbon compound hex-

  9. Naming hydrocarbons • Suffix (second part) depends on the bond between carbon atoms. • Single bond –ane • Double bond –ene • Triple bond –yne

  10. Alkanes

  11. Crude oil • Crude oil is a source of many hydrocarbons • Crude oil is formed from the dead bodies of animals (mainly aquatic) which were living millions of years ago. • These bodies are covered with sand and mud. • Due to changes in temperature and pressure, the animal bodies are changed in to a dark viscous liquid called crude oil(petroleum). • Soil changed into sedimentary rock.

  12. Crude oil • Crude oil is pumped out from the oil wells. • Important substances from crude oil are separated in an oil refinery.

  13. Fractional distillation of crude oil • Various useful substances are separated from crude oil by fractional distillation. Fractions with low boiling points with low density are collected at the top. • Following increase when coming down in the fractionating column: • Density • Molecular mass (No of C atoms) • Viscosity • Colour darker • Boiling point

  14. Fuels • Fuels give out energy. • Coal, natural gas, petrol etc are fuels • Natural gas is mainly methane. • Hydrocarbons burn in air to produce carbon dioxide and water together with energy(heat) • Methane + oxygen  Carbon dioxide + water CH4 + 2O2  CO2 + 2H2O • Ethane + oxygen  carbon dioxide + water 2C2H6 + 7O2  4CO2 + 6H2O

  15. Functional group • Double bond = • Alcohol -OH • Carboxylic acid –COOH • Halide -Cl -Br -I • Group of compounds with similar properties is called HOMOLOGOUS SERIES • Examples: Alkanes, Alkenes, Alcohols, Carboxylic acids etc

  16. Alcohols • Methanol (1Carbon alcohol) • CH3OH • Ethanol (2 Carbon alcohol) • C2H5OH or CH3-CH2-OH • Propanol (3 Carbon alcohol) • C3H7OH or CH3-CH2-CH2-OH

  17. Carboxylic acids • Methanoic acid (1Carbon acid) • HCOOH • Ethanoic acid (2 Carbon acid) • CH3COOH • Propanoic acid (3 Carbon acid) • CH3CH2COOH

  18. Alkanes • Alkanes are saturated hydrocarbons. So they are not reactive. • Alkanes burn in oxygen to form carbon dioxide and water. • CH4 + 2O2  CO2 + 2H2O • Energy is given out when alkanes burn. So alkanes are present in fuels. • Petrol and diesel are mixtures of alkanes.

  19. Substitution reaction • If atoms are replaced by other atoms, the reaction is called substitution reactions. • Alkanes show substitution reaction. Hydrogen atoms are replaced by more reactive halogen atoms in presence of light. • Here light works as a catalyst.

  20. Alkenes • Alkenes are unsaturated compounds having a double bond between carbon atoms. • Alkenes are highly reactive. • They also burn in oxygen to produce carbon dioxide gas and water. • Ethene + Oxygen  Carbon dioxide + Water • C2H4 + 3O2  2CO2 + 2H2O

  21. Addition reaction • Unsaturated compounds undergo addition reaction. • Atoms are added to the double bond to form a single product (No replacement). This kind of reaction is called addition reaction. • During addition reaction, double bond compounds(less stable) change into single bond compounds (stable) • Alkenes Alkanes

  22. Addition of halogen (bromine) • Ethene + Bromine  dibromo ethane • CH2=CH2 + Br2 CH2Br-CH2Br • Addition of hydrogen • Heat and a catalyst (Nickel) are needed for the addition of hydrogen to alkene. • Ethene + Hydrogen  Ethane (Heat & Ni needed) • CH2=CH2 + H2  CH3-CH3 • Addition of water • Heat and high pressure are needed for this. • Ethene + steam  Ethanol • CH2=CH2 + H2O  CH3-CH2-OH

  23. Polymerisation • Small molecules(monomers) join one another to form a large molecule (polymer). • This kind of reaction is called polymerisation. • At high temperature and pressure, alkenes undergo polymerisation to form different polymers (Plastics) • During polymerisation, double bond becomes single.

  24. Ethene  Poly ethene (Polythene) • …CH2=CH2 + CH2=CH2 + CH2=CH2 + CH2=CH2….  -CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2 • The above reaction can be summarised as • nCH2=CH2  -(CH2-CH2)-n • Another example is chloroethene when polymerised, we get polychloroethene (PVC) • nCH2=CHCl  -(CH2-CHCl)-n • Propene when polymerised we get polypropene (another plastic)

  25. Test for unsaturated compounds • Saturated compounds have single bonds between carbon atoms • Unsaturated compounds have a double/triple bond between carbon atoms. • When an unsaturated compound is passed through bromine water, the colour will change from orange brown to colourless. • This is because of the addition reaction with unsaturated compound and bromine. • CH2=CH2 + Br2 CH2Br-CH2Br (orange brown) (colourless)

  26. Alcohols • Common alcohols are methanol, ethanol and propanol • CH3OH, C2H5OH, C3H7OH • Ethanol is present in alcoholic drinks. Also used in hospitals, industries (as a solvent) and different types of medicines. Widely used as fuel for car engines. • Methanol is poisonous • Propanol is a good solvent used to clean audio and video heads.

  27. Ethanol • Two methods of making ethanol are: • Batch process • In this method glucose is fermented using yeast. Enzymes in yeast change glucose into ethanol and carbon dioxide (anaerobic respiration by yeast) • Glucose  ethanol + carbon dioxide • C6H12O6  2C2H5OH + 2CO2 • Ethanol formed is separated by distillation

  28. Continuous process • In this process, ethene is treated with super heated steam at high temperature and pressure in presence of concentrated acid as a catlyst (addition) • CH2=CH2 + H-OH  CH3-CH2OH • Ethene is a by-product during the petroleum industry. • The production of ethanol takes place continuously.

  29. Advantages and disadvantages • Batch process • Advantage: environmental friendly • Disadvantage: Takes long period of time for yeast to ferment • Continuous process • Advantage: quick and continuous production • Disadvantage: can cause pollution and expensive (need of fuel)

  30. Cracking • It is opposite of polymerisation • Large molecules are broken down into small molecules using catalyst or heat. • Most petroleum products are large hydrocarbon molecules. • These large molecules are cracked into small molecules which are present in petrol (5-10 carbon atoms). • Alkenes will be formed when alkanes are cracked

  31. Fermentation: Yeast changes glucose into alcohol and carbon dioxide gas is called fermentation. Fermentation is anaerobic respiration. • Ethene formed as by-product during cracking is useful in the manufacture of ethanol. • C12H26 C8H18 + 2C2H4 (large alkane) (useful alkane) Ethene • Ethanol when burns in oxygen (air), it gives out carbon dioxide, water and energy. • Ethanol + Oxygen  Carbon dioxide + water • C2H5OH + 3O2  2CO2 + 3H2O + Energy

  32. Acids • Important carboxylic acids are: • Methanoic acid, Ethanoic acid and Propanoic acid H-COOH CH3-COOH C2H5-COOH Ethanoic acid is prepared by the oxidation of ethanol using potassium manganate(VII). • C2H5OH + 2(O)  CH3COOH + H2O • Acid present in vinegar is Ethanoic acid. • Alcohol (wine) turns sour if left open in air (acid formation) • Ethanoic acid is a weak acid(Hydrogen ions are given out partially)

  33. Esterification • When an organic acid reacts with an alcohol, ester and water are formed. This is done in presence of conc sulphuric acid.(dehydrating agent) • Example: Ethanol reacts with ethanoic acid will produce ethyl ethanoateester and water. • C2H5OH + CH3COOHC2H5OOCCH3 + H2O Ethanol Ethanoic acid Ethyl ethanoate water • Propanol + Ethonoic acid  Propyl ethanoate+ water • C3H7OH + CH3COOH C3H7OOCCH3 + H2O Propanol Ethanoic acid Ethyl ethanoate water

  34. Methyl propanoateis formed from which alcohol and acid? • Methanol and Propanoic acid • Write formula of Methanol, Propanoic acid and methyl propanoate • CH3OH, C2H5COOH, CH3OOCC2H5 • Write names of any two esters, alcohol and acid from which they are formed and write their formulas. • Esters are sweet smelling substances (found in fruits). So they are used to make perfumes.

  35. Macromolecules • Macromolecules are large molecules (polymers) formed from small molecules (monomers). • Macromolecules are synthetic(man made) or natural. • Synthetic polymers. • Poly ethene, poly propene and chloroetheneare polymers formed by the addition polymerisation (of double bond monomers). • Non biodegradable plastics stay in soil and cause soil pollution. Bio-degradable plastics can be removed by micro organisms.

  36. Condensation polymers • Some polymers are made from non-double bond compounds. • Example: Nylon is a polymer from an amine and acid. Water molecules removed. OR

  37. Another example is Terylene • Water molecules removed

  38. Natural polymers • Mainly carbohydrates, proteins and fats • These are food constituents • Carbohydrates macromolecules such as starch is made up of simple sugars like glucose or fructose. -OH + HO- groups joined here. • Water molecules removed.

  39. Complex carbohydrates when hydrolyse turn into simple sugars back • Starch + water glucose • Hydrolysis is breaking large molecules into smaller ones by adding water. In our body, digestive enzymes help in hydrolysis.

  40. Proteins and fats • Proteins are made up of amino acids. • Many amino acid molecules join to form proteins. • Amino group (-NH2) is basic and acid group (-COOH) is acidic. • So amino group and acid group react to form amide link (peptide bond). Water is removed during the process.

  41. Proteins on hydrolysis give the amino acids. • Fats and oils(lipids) are macromolecules of fatty acids and glycerol. • Glycerol and fatty acids are joined like that in terylene • Fats on digestion (hydrolysis) gives fatty acids and glycerol. • Fats when hydrolyse with alkali we get soaps. • Amino acids from protein molecules are separated and identified by chromatography.

  42. THE END