Q.Chlorobenzene is treated with $\text{Br}_2$ in the presence of $\text{FeBr}_3$. Identify the major organic product and explain why substitution occurs predominantly at the ortho and para positions relative to chlorine even though chlorine deactivates the ring.

$\text{FeBr}_3$ polarises $\text{Br}_2$ into an electrophilic brominating species, which then attacks the chlorobenzene ring. Chlorine's lone pair can donate into the ring by resonance specifically when the electrophile adds at the ortho or para position, stabilising the resulting arenium-ion intermediate at those positions in a way that is not possible for meta attack (no analogous resonance structure exists placing the positive charge adjacent to the chlorine when attack is meta). So although chlorine's strong inductive withdrawal makes the whole ring less reactive than benzene itself (the reaction is slower overall), wherever substitution does occur it is directed almost entirely to ortho and para. Para product predominates over orth …

Separate the two effects explicitly: resonance donation controls where substitution occurs (ortho/para), inductive withdrawal co …

Assuming a deactivating substituent must be meta-directing -- halogens are the classic exception, deactiv …