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Alkanes 2812 1

ALKANES
General · members of a homologous series with general formula CnH2n+2 - non-cyclic only
· saturated hydrocarbons - all carbon-carbon bonding is single
· bonds are spaced tetrahedrally about carbon atoms.



Isomerism The first example of structural isomerism occurs with C4H10. Two structural isomers exist

CH3…

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2 2812 Alkanes


CHEMICAL PROPERTIES OF ALKANES

Introduction · fairly unreactive - their old family name, paraffin, means little reactivity
· consist of relatively strong, almost non-polar covalent bonds
· have no real sites that will encourage substances to attack them


Combustion · alkanes make useful fuels - especially the…

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Pollution Processes involving combustion give rise to a variety of pollutants ...
power stations SO2 emissions produce acid rain
internal combustion engines CO, NOx and unburnt hydrocarbons



Q.4 What does the formula NOx stand for ?




Q.5 Why are the following classed as pollutants ?

· CO…

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4 2812 Alkanes


Breaking covalent bonds
There are three different ways to split the shared pair of electrons in an unsymmetrical covalent bond.



UNEQUAL SPLITTING

+ + - produce IONS


}
a) X Y X Y

known as HETEROLYSIS or
- + HETEROLYTIC FISSION
b) X Y X + Y…

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Alkanes 2812 5


Chlorination
of methane Reagents chlorine and methane

Conditions UV light or sunlight - heat could be used as an alternative energy source

Equation(s) CH4(g) + Cl2(g) ----> HCl(g) + CH3Cl(g) chloromethane

CH3Cl(g) + Cl2(g) ----> HCl(g) + CH2Cl2(l) dichloromethane

CH2Cl2(l) + Cl2(g) ----> HCl(g) + CHCl3(l) trichloromethane…

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6 2812 Alkanes

CRACKING
Process · involves the breaking of C-C (and C-H) bonds in alkanes
· converts heavy fractions into smaller, higher value products such as alkenes

· two types THERMAL Free radical mechanism
CATALYTIC Carbocation (carbonium ion) mechanism



THERMAL · HIGH PRESSURE ... 7000 kPa
· HIGH TEMPERATURE…

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The Petrochemical Industry

Crude Oil In the past, most important organic chemicals were derived from coal. Nowadays, natural
gas and crude petroleum provide an alternative source.

· the composition of crude petroleum varies according to its source
· it is a dark coloured, viscous liquid
· consists…

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