Question

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

Answer 1

Hint: Proceed by considering the exceptional case of halogens in priority order of resonance, hyperconjugation and induction in case of electrophilic aromatic substitution. Also, keep in mind the case or ring activation and deactivation.

Complete step-by-step solution -

Electrophilic Aromatic Substitution reaction is mostly seen in benzene and its derivatives.
The most common named reactions in Electrophilic Aromatic Substitution includes-
Halogenation (Chlorination/ Bromination/ Iodination)
Nitration
Sulphonation
Friedel Craft Acylation
Friedel Craft Alkylation
As we know, the effect of resonance dominates over inductive effect.
Any compound containing a lone pair of electrons tends to show resonance over the ring and increase its electron density. Chlorine has a lone pair of electrons and hence, shows +R effect.
But its electronegativity is comparatively high (around 3.16). So, it has a higher tendency to pull electrons towards itself. Therefore, the -I effect in case of chlorine dominates over +R effect. Thus, the net effect is deactivation of the ring.
Also, Inductive effect (-I) destabilised the intermediate carbocation. This results in ortho-para directing the nature of chlorine in electrophilic aromatic substitution reaction.
Therefore, we can conclude that chlorine, being an electron withdrawing group, still acts as an ortho-para directing group in the case of electrophilic aromatic substitution.

Additional Information:
Dominance order: Resonance > Hyperconjugation > Induction

Note: This exception, i.e. being an electron withdrawing group, it is ortho-para directing in electrophilic aromatic substitution reaction – is seen in all halogens. To summarize –
(1). Activators are ortho-para directing
(2). Deactivators (except halogens) are meta-directing
(3). Halogens are deactivators but ortho-para directing.