Organic chemistry
IGCSE Chemistry 0620
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 to another Carbon atom
to form long Carbon chains.
 Because of this there are huge number of organic
compounds.

Saturated and unsaturated compounds
If all bonds between carbon atoms are single,
the compounds are saturated compounds.
 If a double bond is present between carbon
atoms, the compounds are called unsaturated.
 In saturated compounds, all four valencies of
carbon atoms are used up.
 So saturated compounds are not 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


Single bond hydrocarbons are called ALKANES
Alkanes have a general formula:
 CnH(2n+2) where n is the number of carbon atoms.


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Methane CH4
Butane C4H10
Ethane C2H6
Pentane C5H12
Propane C3H8
Hexane C6H14
Double bond hydrocarbons are called ALKENES
 Alkenes have a general formula:


CnH2n where n is the number of carbon atoms.

Ethene C2H4
Pentene C5H10

Propene C3H6
Hexene C6H12
Butene C4H8

https://www.youtube.com/watch?v=Sfm3e
He57PU
Formula of Saturated Hydrocarbons (Alkanes)
Unsaturated compounds (Alkenes) have free
valencies with carbon atoms.
 Second bond in the double bond is weak and
temporary.
 So if other atoms available, unsaturated
compounds are very reactive.

Formula of unsaturated compounds (Alkenes)
Test to find if a compound is saturated or
unsaturated
Mix the compound with bromine water.
(Bromine water is red brown in colour)
 If the hydrocarbon is unsaturated (alkene),
it will react with bromine in bromine
water and becomes colourless.
 If the hydrocarbon is saturated (alkane),
no reaction will take place with bromine
and colour remains the same

Video

https://www.youtube.com/watch?v=1r9aY
S4Ndac
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
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



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
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Fuels give out energy.
Coal, natural gas, petrol etc are fuels
Natural gas (petroleum 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.
 CH4 + Cl2  CH3Cl + HCl

UV
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

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)
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Esterification
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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
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.

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.

Polymerisation
Small molecules(monomers) join one
another to form a large molecule (polymer).
 This kind of reaction is called
polymerisation.
 1. Addition 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)

2. Condensation polymers
Some polymers are made from non-double bond
compounds.
 Example: Nylon is a polymer from an amine and acid. Water
molecules removed. The bond formed is called amide

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.
THE END