What are Alkenes?

Alkenes are unsaturated hydrocarbons that contain at least one double bond between carbon atoms. The same prefixes as for alkanes are used according to the number of carbon atoms, but the ending "-ane" is changed to "-ene".

Rules for naming alkenes

To name alkenes correctly, follow these rules:

1. Identify the main chain, which must contain the double bond (even if it is not the longest).
2. Number the chain so that the double bond receives the lowest possible locant.
3. Indicate the position of the double bond with a number before the alkene name.
4. Identify and name the branches (alkyl radicals).
5. List the branches alphabetically (ignoring di-, tri-, etc. prefixes).

Examples of alkenes

1-butene:

A butene with the double bond at position 1.

2-pentene:

Main chain: pentene. The double bond is between carbons 2 and 3.

3-methyl-1-butene:

A butene with the double bond at position 1 and a methyl group at position 3.

4-methyl-2-hexene:

The main chain is a hexene with the double bond at position 2 and a methyl group at position 4. Number from the left to give the lowest position to the double bond.

penta-1,3-diene:

The main chain is a diene with double bonds at positions 1 and 3. Number from the left to give the lowest positions to the double bonds.