Organic chemistry IGCSE Chemistry 0620
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’.
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.
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)
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.
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-
Naming hydrocarbons • Suffix (second part) depends on the bond between carbon atoms. • Single bond –ane • Double bond –ene • Triple bond –yne
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.
Crude oil • Crude oil is pumped out from the oil wells. • Important substances from crude oil are separated in an oil refinery.
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
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
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
Alcohols • Methanol (1Carbon alcohol) • CH3OH • Ethanol (2 Carbon alcohol) • C2H5OH or CH3-CH2-OH • Propanol (3 Carbon alcohol) • C3H7OH or CH3-CH2-CH2-OH
Carboxylic acids • Methanoic acid (1Carbon acid) • HCOOH • Ethanoic acid (2 Carbon acid) • CH3COOH • Propanoic acid (3 Carbon acid) • CH3CH2COOH
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.
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.
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
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
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
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.
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)
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)
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.
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
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.
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)
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
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
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)
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 + CH3COOHC2H5OOCCH3 + H2O Ethanol Ethanoic acid Ethyl ethanoate water • Propanol + Ethonoic acid Propyl ethanoate+ water • C3H7OH + CH3COOH C3H7OOCCH3 + H2O Propanol Ethanoic acid Ethyl ethanoate water
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.
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.
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
Another example is Terylene • Water molecules removed
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.
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.
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.
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.