A2 AQA CHEM4 3.4.6

3.4.6 Aromatic Chemistry

Bonding

·         C₆H₆ with delocalised electrons above and below the plane (one of the p-orbital electrons for each carbon is not involved in bonding since carbon bonds with 1 hydrogen

·         Planar structureà All bond angles are 120^o (trigonal planar)

·         Bond lengths are identical. The actual length is in between the length of C-C and C=C (intermediate length)

Delocalisation stability

·         Benzene is more stable than cyclohexatriene (hypothetical)

·         Hypothetical  ΔH would be -360KJmol^-1 but the ΔH of benzene is -208KJmol^-1 which means it is 152KJmol^-1 less exothermic and therefore more stable

·         This stability is caused by the delocalised electrons (hence the difference of 152 is the delocalisation enthalpy)

Electrophilic substitution

·         Electrophilic attack in arenes (containing one or more benzene rings) results in substitution of one of the hydrogens…therefore a H⁺ will be eliminated

·         Delocalised electrons in benzene ring act as area…