Which of the following compounds will not give azo coupling reaction with benzene diazonium chloride?
Correct Answer :
Nitrobenzene
Solution :
The correct option is Nitrobenzene.
Azo coupling is an electrophilic aromatic substitution reaction where a diazonium ion acts as the electrophile. The benzene diazonium cation is represented as:
Due to the delocalization of the positive charge over the nitrogen atoms, the diazonium ion is a relatively weak electrophile.
Because the diazonium ion is a weak electrophile, it requires a highly activated aromatic ring to react. Aromatic rings are activated by strong electron-donating groups that increase electron density on the ring through resonance.
Examples of such activating groups include the hydroxyl group:
present in phenol, and the amino group:
present in aniline and o-toluidine. Therefore, phenol, aniline, and o-toluidine readily undergo azo coupling reactions.
In contrast, nitrobenzene contains a nitro group:
The nitro group is a strongly electron-withdrawing group due to both resonance and inductive effects. It deactivates the benzene ring by drastically reducing its electron density. As a result, the deactivated ring of nitrobenzene is not nucleophilic enough to attack the weak benzene diazonium electrophile, and no azo coupling reaction takes place.
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