Bromine water is an orange solution of bromine. It becomes colourless when it is shaken with an alkene. Alkenes can decolourise bromine water, but alkanes cannot. The slideshow shows this process.

The table shows the first four alkenes, their molecular formulae, displayed formulae, structural formulae as well as a drawing of their ball-and-stick constructional models.

The carbons of the alkene functional group, the site of unsaturation, are in the rounded rectangle. Since there is only one double bond, oleic acid is an example of a monounsaturated fatty acid.