ORGANIC CHEMISTRY
3.2 Alkanes
INSTRUCTOR: Dr Aksanoglu
AQA A LEVEL
● Alkanes are saturated hydrocarbons
○ They only contain carbon-carbon and carbon-hydrogen single bonds
● The longer the carbon chain, the higher the boiling point:
○ As there is a larger surface area
○ So more electrons, so stronger Van Der Waal’s forces
● For isomers - The more branched the carbon chain, the lower the boiling point
○ Due to weaker Van Der Waal’s forces (molecules are unable to pack as close together)
● Crude Oil is a mixture of different hydrocarbons
● Petroleum is a mixture consisting mainly of alkane hydrocarbons that can be separated by fractional
distillation.
● Deposits of crude oil and natural gas usually occur together
○ Formed by the slow decay of marine animals and plants
○ Formed over millions of years
○ Under heat and pressure, in the absence of air
● The exact composition of crude oils vary around the world
○ They are complex mixtures consisting of many alkanes
○ E.g. Cycloalkanes, some aromatics, and other compounds containing some S and O
● It has no use in its raw form (and is very unreactive) so must be separated at an oil refinery
○ The steps of the separation process (Fractional Distillation):
1. The mixture is vaporised and fed into the fractionating column
2. Vapours rise, cool and condense
3. Products are siphoned off for different uses
1
3.2 Alkanes
INSTRUCTOR: Dr Aksanoglu
AQA A LEVEL
● Alkanes are saturated hydrocarbons
○ They only contain carbon-carbon and carbon-hydrogen single bonds
● The longer the carbon chain, the higher the boiling point:
○ As there is a larger surface area
○ So more electrons, so stronger Van Der Waal’s forces
● For isomers - The more branched the carbon chain, the lower the boiling point
○ Due to weaker Van Der Waal’s forces (molecules are unable to pack as close together)
● Crude Oil is a mixture of different hydrocarbons
● Petroleum is a mixture consisting mainly of alkane hydrocarbons that can be separated by fractional
distillation.
● Deposits of crude oil and natural gas usually occur together
○ Formed by the slow decay of marine animals and plants
○ Formed over millions of years
○ Under heat and pressure, in the absence of air
● The exact composition of crude oils vary around the world
○ They are complex mixtures consisting of many alkanes
○ E.g. Cycloalkanes, some aromatics, and other compounds containing some S and O
● It has no use in its raw form (and is very unreactive) so must be separated at an oil refinery
○ The steps of the separation process (Fractional Distillation):
1. The mixture is vaporised and fed into the fractionating column
2. Vapours rise, cool and condense
3. Products are siphoned off for different uses
1
