Q.Among the following, which is meta directing group?
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Start your 14-day free trial to unlock the full solution →-NO2 withdraws electron density from the benzene ring by both induction and resonance, so it deactivates the ring and directs the next electrophile to the meta position.
When benzene undergoes electrophilic aromatic substitution, an existing substituent controls where the second group goes by stabilising (or destabilising) the intermediate arenium (sigma-complex) cation formed at the ortho, meta and para positions.
Groups such as -NH2, -OCH3 and -OH have a lone pair on the atom attached to the ring. This lone pair can be donated into the ring by resonance (+M effect), which is strongest when the electrophile attacks ortho or para to the group, because only then can the positive charge in the intermediate be placed on the very carbon bearing the substituent and be neutralised by the lone pair. These groups are therefore activating and ortho/para directing (even though -OH and -NH2 are also weakly -I, their +M effect dominates).
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