Last modified on 18 September 2012, at 14:01

A-level Chemistry/OCR/Arenes

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 'pi' electron into a 'pi' bond. The electrons become '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, when compared to Phenol. 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.

Benzene can be nitrated. In order to be nitrated it must be combined with a nitrating mixture of concentrated Sulfuric acid and Nitric acid. The sulphuric acid acts like a catalst. Therefore, it is regenerated at the end of the reaction. Benzene is 152kJ/mol more stable than expected. Therefore, it can not polarise a molecule. Sulphuric acid generates the nitronium ion -(NO2+) which can then go further on in the reaction and the nitration reaction can occur.