Here's why:
* Benzene's Stability: Benzene has a very stable structure due to its delocalized pi electrons. This makes it relatively unreactive towards typical electrophilic attack.
* Chlorine as a Deactivating Group: When chlorine is attached to a benzene ring, it acts as a deactivating group. This means it reduces the electron density in the ring, making the benzene less reactive towards further electrophilic substitution.
* Inductive Effect: Chlorine is more electronegative than carbon. It pulls electron density away from the benzene ring through an inductive effect. This makes the ring less electron-rich and less susceptible to electrophilic attack.
* Resonance Effect: Chlorine can also participate in resonance with the benzene ring, further reducing the electron density in the ring.
In Summary: Chlorine, when attached to benzene, makes the ring less reactive towards further electrophilic substitution due to its deactivating effect through inductive and resonance effects.
Important Note: While chlorine makes benzene less reactive compared to unsubstituted benzene, it still undergoes electrophilic substitution reactions, just at a slower rate.
