Benzene is the most common Arene. It has a hexagonal shape. The electrons in a benzene molecule are in 'pi' bonds. Each of the carbon atoms contribute one electron into a 'pi' bond. The electrons are 'delocalised' as they are spread out over all 6 'pi' bonds within the benzene molecule.

To break the 'pi' bonds in benzene compounds requires a lot of energy and therefore they do not always react easily. The majority of their reactions are substitution reactions and there are 4 groups known as the 4 ations that are important to this module.

The first of the 4 ations are nitroarenes. The nitrogroups are substituted for hydrogen atoms on the benzene ring. They are used for drugs and dyes and also explosives such as TNT.