4. Organic Compounds
a. Introduction
b. Crude Oil
c. Alkanes
d. Alkenes
e. Alcohols
f. Carboxylic acids
g. Esters
h. Synthetic polymers
a. Introduction
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Hydrocarbon: Compound that contains only hydrogen and carbon atoms
Example:
Diagram showing different examples on hydrocarbons
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Representing Organic Molecules
Definitions
Example: Ethane (C2H6)
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Representing Organic Molecules
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Homologous series: A series of organic compounds that has similar features:
o Same general formula
o Same functional group
o Similar chemical reactions
o Physical properties show graduations
o Each member differs in molecular formula from the next by CH2
Example: Alkanes
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
Example: Alcohols
CH3OH
C2H5OH
C3H7OH
C4H9OH
C5H11OH
C6H13OH

Functional group: A group of atoms bonded in a specific arrangement that controls the
property of the homologous series:
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Isomerism: Compounds that have the same molecular formula but different structural formulae
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Organic Compounds: Naming & Formulae
Naming Compounds
Note: Organic compounds are named according to IUPAC system

The first part of the name comes from the number of carbon atoms in the hydrocarbon, the
second part comes from the functional group present
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Example:
Further rules
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When there is more than one carbon a functional group can be located it is important to
distinguish which carbon the functional group is on. Each carbon is numbered and these
numbers are used to describe where the functional group is
When 2 functional groups are present di- is used as a prefix to the second part of the name
Branching also needs to be considered, the carbon atoms with the branches are described by
their number
When the location of functional groups and branches needs to be described the functional
group takes precedence so the functional group has the lowest number
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Examples
Displayed & Structured Formulae
Displayed formula:
A graphic representation that shows the symbols for each atom in a compound, with straight
lines joining them to represent the covalent bonds.
Structural Formula:
A condensed representation that shows the symbols for each atom in a compound, with straight
lines joining them to represent the covalent bonds.
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Questions:
Name the following compounds according to the IUPAC system
a.
b.
c.
d.
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Classifying Reactions of Organic Compounds
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1.Substitution: A reaction where one atom is swapped with another atom
o Example: Methane reacts with bromine under ultraviolet light

2.Addition: A reaction in which one molecule combines with another to form a larger
molecule with no other products
o Example: Bromine will react with ethene and the bromine molecule will react and add
across the double bond of the ethene
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3.Combustion: A reaction in which one molecule combines with another to form a larger
molecule with no other products
o Example: Alkenes burn when heated in air of oxygen
o If there is an unlimited supply of air / oxygen, the products are carbon dioxide and
water:
CH4 + 2O2 → CO2 + 2H2O
C3H8 + 5O2 → 3CO2 + 4H2O
o
This is termed complete combustion
o
If there is a limited supply of air / oxygen, the products are carbon monoxide and
water:
CH4 + ½O2 → CO + 2H2O
o
This is termed incomplete combustion
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b. Crude Oil
Crude oil: A mixture of hydrocarbons.

Thick, sticky, black liquid that is found under porous rock (under the ground and under
the sea).
If any fraction from crude oil is burned, then carbon dioxide and water is produced – this shows
that crude oil is a complex mixture of hydrocarbons:
Fractional Distillation
Fractional distillation: To separate two or more liquids that are miscible with one another
Industrial process of fractional distillation:
The process of fractional distillation to separate crude oil in a fractionating column
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Explanation:
Fractional distillation is carried out in a fractionating column.
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In the fractionating column, it is hot at the bottom and cool at the top.
Crude oil will enter the fractionating column and will be heated so vapours will rise and
evaporate.
Vapours of hydrocarbons with very high boiling points will immediately turn into liquid and
are tapped off at the bottom of the column.
Vapours of hydrocarbons with low boiling points will rise up the column and condense at the
top to be tapped off.
The different fractions will condense at different heights according to their boiling points and
will be tapped off as liquids. All the fraction are mixtures of different kinds of hydrocarbon.
To conclude the smaller hydrocarbons are collected at the top of the fractionating column as gases.
The bigger hydrocarbons are collected at the lower sections of the fractionating column.
Trends of Crude Oil Fractions
Viscosity: Viscosity refers to the ease of flow of a liquid. High viscosity liquids are thick and flow
less easily. If the number of carbon atoms increases, the attraction between the hydrocarbon
molecules increases, which results in the liquid becoming more viscous – this is because of the
increasing length of the hydrocarbon chains. The liquid flows less easily with the increasing
molecular mass.
Colour: As carbon chain length increases, liquid colour gets darker, as it becomes thicker and more
viscous.
Melting point/boiling point: As the molecules get larger, the intermolecular attraction becomes
greater, so more energy in the form of heat is needed to separate the molecules. With increasing
molecular size there is an increase in boiling point.
Volatility: Volatility refers to the tendency of a substance to vaporise. As their molecular size
increases, hydrocarbon liquids become less volatile
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Fuel
Fuel: Substance which when burned, releases heat energy

This heat can be transferred into electricity, which we use in our daily lives
Complete combustion of hydrocarbons: During the complete combustion of hydrocarbons,
carbon dioxide and water will be produced:
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Carbon will oxidise to form carbon dioxide
Hydrogen will oxidise to water
Hydrocarbon + Oxygen → Carbon dioxide + Water
Incomplete combustion: Occurs when there is a limited supply of air so that elements in the
fuel do not fully react with Oxygen

During the incomplete combustion of hydrocarbons, water will still be produced but
instead of carbon dioxide, carbon monoxide (soot) will form
Hydrocarbon + Oxygen → Carbon Monoxide + Water
Carbon Monoxide
Carbon monoxide: A poisonous gas that is colourless and odourless, produced during
incomplete combustion:
Hydrocarbon + Oxygen → Carbon monoxide + Water
Effect of Carbon monoxide on blood:

When carbon monoxide is produced by incomplete combustion, it is absorbed in the
lungs and this reduces the capacity of the blood to carry oxygen.
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Acid Rain
Formation of oxides of nitrogen in car engines:
 When fuels are burned in car engines, high temperatures are reached which allows
Nitrogen and Oxygen from the air to combine to produce Nitrogen monoxide:
Nitrogen + Oxygen → Nitrogen Monoxide
N2 (g) + O2 (g) → 2NO (g)

When this Nitrogen monoxide is released from the engines of vehicles, it combines
with Oxygen in the air to form Nitrogen dioxide:
Nitrogen Monoxide + Oxygen → Nitrogen Dioxide
2NO (g) + O2 (g) → 2NO2 (g)

Both Nitrogen monoxide and Nitrogen dioxide are produced in car engines as a result
and is referred to as NOx
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Hydrocarbon fuels: Impure Hydrocarbon fuels contain Sulfur compounds
Combustion of Hydrocarbon fuels:
During the combustion of Hydrocarbon fuels, impurities such as Sulfur compounds
will be oxidised to produce sulfur dioxide:
Combustion of Hydrocarbon Fuels
Sulfur + Oxygen → Sulfur Dioxide
S (g) + O2 (g) → SO2 (g)

Acid rain: Rain that contains dissolved acidic gases such as sulfur dioxide and oxides
of nitrogen. The pH value of normal rain is slightly below 7. The pH value of acid rain
is approximately 3.4.

Sulfur dioxide will react with oxygen and dissolve in water droplets in clouds, forming
dilute sulfuric acid which will cause acid rain:

Sulfur Dioxide + Oxygen + Water → Sulfuric Acid
2SO2 (g) + O2 (g) + H2O (l) → 2H2SO4 (aq)
Nitrogen oxides will dissolve in water droplets in clouds, forming dilute Nitric acid
and Nitrous acid, causing acid rain:
Nitrogen Dioxide + Water → Nitric Acid
NO2 (g) + H2O (l) → HNO3 (aq)
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Catalytic Cracking
Long-chain hydrocarbons: large number of hydrocarbon molecules. More viscous and less
flammable so less useful.
Short-chain hydrocarbons: small numbers of hydrocarbon molecules.
Cracking is simply splitting of larger molecules to simpler ones.
Explanation:
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Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful
hydrocarbon molecules.
Fractions containing large hydrocarbon molecules are heated at 600 – 700°c to vaporise
them.
Vapours will then pass over a hot catalyst of silica or alumina
This process breaks covalent bonds in the molecules, causing thermal decomposition
reactions.
As a result, cracking produces smaller alkanes and alkenes. The molecules are broken up in a
random way which produce a mixture of alkanes and alkenes.
Why Cracking is Necessary
Although there is use for each fraction after the fractional distillation of crude oil, the amount of
longer chain hydrocarbons produced is far greater than needed.
However, the amount of shorter chain hydrocarbons produced is far less than needed (e.g. gasoline
fraction) and there is a higher demand for shorter chain hydrocarbons. This is why cracking is
necessary to increase the supply of shorter chain hydrocarbons.
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Short chain hydrocarbons burn well and flow well.
Cracking is used to produce petrol for cars.
Cracking also produces alkenes which are raw material in the plastic industry.
Cracking is used to produce hydrogen gas which is a raw material in manufacture of
ammonia in Haber process.
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Example: The Cracking of hexane (C6H14) to produce butane (C4H10) and ethene
(C2H4):
C6H14 (g) →
C4H10 (g) +
C2H4 (g)
Ethene: The ethene can be used to make poly(ethene), a type of plastic.
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Questions:
1) Many hydrocarbons are used as fuels. There are problems associated with this use.
(i) Explain how the combustion of a hydrocarbon can lead to the formation of a poisonous
gas.
(2)
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
(ii) State why this gas is poisonous to humans.
(1)
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2) Fuels used in cars often have sulfur compounds removed.
Explain how the combustion of these fuels in car engines still leads to the formation of acid
rain.
(4)
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