30.1.1—Chemistry of arenes

Benzene and methylbenzene are arenes: aromatic rings with delocalised π electrons. Their characteristic reactions replace a ring hydrogen rather than add across the ring, preserving aromatic stabilisation.

Typical syllabus reactions include nitration, halogenation and Friedel–Crafts-type substitution. A methyl group activates the ring and directs substitution mainly to the 2- and 4-positions relative to itself.

Benzene gives nitrobenzene on nitration; methylbenzene gives a mixture of 2- and 4-nitromethylbenzene under comparable conditions.

Arene substitution is not ordinary alkene addition: the ring regains aromaticity after the substitution step.