CBSE Class 12-science Answered

• Chlorine withdraws electrons through inductive effect and releases electrons through resonance.

 

• Through inductive effect, chlorine destabilises the intermediate carbocation formed during the electrophilic substitution.

 

• Through resonance, halogen tends to stabilise the carbocation and the effect is more pronounced at ortho- and para- positions.
• The inductive effect is stronger than resonance and causes net electron withdrawal and thus causes net deactivation.
• The resonance effect tends to oppose the inductive effect for the attack at ortho- and para positions and hence makes the deactivation less for ortho- and para attack.
• Reactivity is thus controlled by the stronger inductive effect and orientation is controlled by resonance effect.