Question

For an electrophilic substitution reaction, the presence of a halogen atom in the benzene ring _______.

• A. Directs the incoming electrophile to meta position by increasing the charge density relative to ortho and para position.
  
• B. Deactivates the ring by resonance.
  
• C. Deactivates the ring by inductive effect.
  
• D. Increases the charge density at ortho and para position relative to meta position by resonance.
  

Answer 1

Answer: (C), (D)

Increases the charge density at ortho and para position relative to meta position by resonance.


For an electrophilic substitution reaction, the presence of halogen atoms in the benzene ring deactivates the ring by inductive effect $(-Ieffect)$ and increases the charge density at ortho and para position relative to meta position by resonance

$\bullet$ From these structures, it is clear that due to $+R/+M$ effect of $Cl$, electron density increases at ortho and para positions as compared to meta position, although it is not effective due to the fact that bigger orbital electrons from $Cl$ are being delocalised.


Also, halogen being electronegative pulls the electron from the benzene ring showing $–I$ effect and deactivating it. Hence, electrophiles majorly attack the ortho or para position in aryl halides.