Organic Chemistry - alkanes and alkenes

A quick overview of alkanes, alkenes, isomers, reactions of alkenes and the bromine test for alkenes.

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  • Created on: 28-04-09 19:40
Preview of Organic Chemistry - alkanes and alkenes

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Organic Chemistry ­ alkanes and alkenes
Organic chemistry is the chemistry of carbon.
Hydrocarbons are a compound made of hydrogen and carbon only
Alkane ­ a type of hydrocarbon
Methane = CH4 ­ the simplest type of alkane
The formula for alkanes is CnH2n+2
Common alkanes:
Ethane = C2H6
Propane = C3H8
Butane = C4H10
Isomers have the same molecular formula but different structures
Alkenes ­ an unsaturated hydrocarbon
Unsaturated means the compound has at least 1 double bond. In the alkenes case, this must be a
carbon=carbon double bond.
Ethene = C2H4 ­ the simplest type of alkene.
It is impossible to have `methene' as there must be two carbon atoms for a double bond.
The formula for alkenes is CnH2n
Common alkenes:
Propene = C3H6
Butene = C4H8
Alkenes are unsaturated so you can add hydrogen by breaking the double bonds.
All the bonds off a carbon molecule with a double bond are at 120° to each other.
Reactions of alkenes:
This diagram shows an unsaturated
hydrocarbon (ethene) going through
the process of `hydrogenation' ­
where the double carbon bond is broken and the ethene becomes saturated. This is an example of an
addition reaction.
Testing for alkenes
To test for an alkene, simply add bromine water to the alkene. If the brown colour disappears then the
solution is an alkene. If it doesn't the compound cannot be an alkene.


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