Question

Although chlorine is an electron withdrawing group, yet it is orthopara-directing in electrophilic aromatic substitution reactions. Why?

Answer 1

Chlorine withdraws electrons through inductive effect and releases electrons through resonance. Through inductive effect, chlorine destabilizes the intermediate carbocation formed during the electrophilic substitution.






Through resonance, halogen tends to stabilize the carbocation and the effect is more pronounced at ortho-and para-positions.But in case of chlorine the inductive effect is more dominant than resonance and causes net deactivation.

The resonence 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.

Hence, chlorine is an electron withdrawing group,but it is ortho-para-directing in electrophilic aromatic substitution reactions.