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 hydrogen only.
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

12. 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.

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

14. 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

16. 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

17. 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

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

19. Carboxylic acids Methanoic acid (1Carbon acid) HCOOH
CH3COOH
Propanoic acid (3 Carbon acid)
CH3CH2COOH

20. 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.

21. 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.

23. 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

24. 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

25. 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

26. 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.

27. Ethene  Poly ethene (Polythene)  -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)

28. 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)

29. 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.

30. 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

31. 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.

32. 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)

33. 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

34. Ethanol + Oxygen  Carbon dioxide + water
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.
C12H  C8H C2H4
(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

35. 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)

36. 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 ethanoate ester 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

37. Methyl propanoate is 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.

38. 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 chloro ethene are 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.

39. 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

40. Another example is Terylene
Water molecules removed

41. 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.

42. 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.

43. 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.

44. 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.

45. THE END