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

Explanation

Chlorine is an electron withdrawing group and has -I (inductive) effect. Therefore, it withdraws electrons from the benzene ring and tends to destabilize the intermediate carbocation formed during the electrophilic substitution reaction. The intermediate carbocations for ortho- and para-attacks are shown below :

However, the lone pairs of electrons on the chlorine atom stabilise the intermediate carbocation due to resonance :

Since -I effect of Cl is stronger than its +R effect, therefore, causes electron withdrawal and this causes net deactivation. The resonance effect tends to oppose the inductive effect for attack at ortho and para position and hence makes deactivation less for ortho-and para-attack. Thus, we can say that the reactivity is controlled by the stronger inductive effect and orientation is controlled by the resonance effect. Thus, although chlorobenzene is less reactive than benzene but it is ortho, para directing in electrophilie substitution reaction.