A level Chemistry revision: Most organic compounds can be named using the IUPAC method. With this method, three features on the molecule are described:

• the longest straight carbon chain
• the length and positioning of any branches
• the nature and position of any functional groups

The longest straight chain on the molecule- A level chemistry revision

One of the prefixes in the table below indicates the longest straight chain present on a molecule.

The length and positioning of any branches- A level chemistry revision

A lot of carbon chains are branched. The following prefixes indicate the presence of a branch:

• Methyl
• Ethyl

The positioning of the branch is specified according to how many carbon form the straight chain that it is attached to. The carbon chain is numbered starting from either the carbon closest to the functional group or, if there is no functional group, from the end closest to the branch.

• 2-methylbutane
• 2,2-dimethylpropane
• 2-methyl, 3-ethylpentane

A lot organic compounds can be represented in different ways due to notation or bonds being rotated. Butane for example.

The nature and position of any functional groups- A level chemistry revision

• Alkanes end with -ane.

? Methane

? Ethane

? Propane

? Butane

• Alkenes end with -ene. If the straight chain of carbon consists of 4 or more atoms then the positioning of the C=C double bond has to be specified. The carbon atoms are numbered, beginning with the end that is closest to the double bond. The carbon atom with the lowest number making up the double bond is indicated before the -ene.

? Ethene

? Propene

? But-1-ene

• Haloalkanes have the prefix chloro-, bromo- or iodo- and end with -ane. If a straight carbon chain consists of three of more carbons then the positioning of the halogen atom has to be specified. The atoms are numbered starting with the one closest to the halogen atom and the number of carbon atom attached to the halogen is indicated before the prefix.

? Chloroethane

? 2-bromopropane

? 1-iodopenthane

Unless composed of one carbon atom, the positioning of all halogens within dihaloalkanes needs to be specified. If the same type of halogen occurs more than once on a molecule, a prefix must be used in correspondence with the number of repetitions: di for two, tri for three, and tetra for four.

? 1, 1-dichloroethane

? 1,2-dichloroethane

? 1-bromo, 2-chloropropane