Aryl halides such as chlorobenzene are far less reactive towards nucleophilic substitution than alkyl halides because
- A. the benzene ring repels all nucleophiles equally
- B. chlorine is not electronegative in aromatic compounds
- C. a lone pair on the halogen is delocalised into the ring, giving the carbon to halogen bond partial double bond character
- D. aryl halides are ionic
Explanation
Overlap between the halogen lone pair and the ring pi system shortens and strengthens the bond, so the halogen is a much poorer leaving group and substitution requires extreme conditions of temperature and pressure. The carbon involved is also sp2 hybridised and holds its electrons more tightly. This is why chlorobenzene does not give a precipitate with silver nitrate on warming while chloroethane does.