Explain the relative resistance to bromination of benzene compared with alkenes.

Benzene has a delocalised pi system in which p orbitals of all carbon atoms overlap above and below the carbon ring. Alkenes, however, have localised pi-orbital overlaps between two carbon atoms. The electron density in the localised system is much greater than the delocalised system in benzene. This greater electron density in alkenes allows a dipole to be induced more readily in bromine and thus makes alkenes more susceptible to electrophilic attack. The electron density in benzene's pi system is not significant enough to produce an electrophile, and thus benzene does not readily undergo electrophilic substitution.