3.10 Aromatic chemistry

Aromatic chemistry takes benzene as an example of this type of molecule and looks at the structure of the benzene ring and its substitution reactions.

Electrophilic substitution mechanism in aromatic chemistry - Electrophilic attack on benzene rings (arene compounds) results in substitution, limited to monosubstitutions. Nitration is an important step in synthesis e.g. manufacture of explosives and formation of amines from which dyestuffs are manufactured Students should know the electrophilic substitution mechanism of nitration, including the generation of the nitronium ion. Friedel–Crafts acylation reactions are also important steps in synthesis. Students should know the electrophilic substitution mechanism of acylation using
Bonding (aromatic chemistry) - The nature of the bonding in a benzene ring, limited to planar structure and bond length intermediate between single and double. Delocalisation of p electrons makes benzene more stable than the theoretical molecule cyclohexa-1,3,5-triene. Students should be able to: • use thermochemical evidence from enthalpies of hydrogenation to account for this extra stability • explain why electrophilic substitution reactions occur in preference to addition reactions