Discuss the reactivity benzene, chlorobenzene, toluene and phenol in electrophillic aromatic substitution

Phenol > Toluene > Benzene > Chlorobenzene.

The reactivity of the ring is dependant on how electron rich it is, as this determines the extent to which the (positively charged) electrophile can attack the ring. Therefore chlorobenzene is the least reactive as chlorine is more electronegative than hydrogen meaning it is electron withdrawing so reduces the electron density of the ring making chlorobenzene the least reaction. Toluene and Phenol are more reactive than benzene since their groups add electron density to the ring. Toluene's methyl group adds electron density through the inductive effect, and the hydroxyl group in phenol can delocalise one of the lone pairs on the oxygen atom into the ring (demonstrated on the whiteboard). These different forms of donation increase the electron density of the ring which makes them more reactive in electrophillic substitution than benzene.