Which substituent on a benzene ring acts as a deactivating group yet directs an incoming electrophile to ortho and para positions?
Answer and explanation
Correct answer: D.
- Step 1: Halogens () possess strong electron-withdrawing inductive effects () due to high electronegativity, which deactivates the aromatic ring toward electrophilic substitution.
- Step 2: However, halogens also possess non-bonding lone pairs capable of resonance donation into the ring during transition state formation.
- Step 3: This resonance stabilization of the arenium intermediate operates specifically at the ortho and para positions, making halogens weakly deactivating but ortho/para-directing.
Answer
(chlorine).
Why not the others: is strongly deactivating and meta-directing; is strongly activating and ortho/para-directing; is activating and ortho/para-directing.
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