Explain the relative resistance to bromination of benzene compared to phenol and compared to cyclohexene.

Within benzene the electrons within the pi-system are delocalised. This means the electrons are spread across the whole ring and has a lower electron density making it less susceptible to electrophilic attack. In comparison, phenol has an OH group which is partially delocalised into the benzene ring making it more electron dense than benzene and therefore more susceptible to electrophiles. Similarly, cyclohexene has three localised electrons in double bonds, meaning it also is more electron dense and like phenol can induce a dipole in Br2, unlike benzene. (includes diagrams in explanation)