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A p-nitrophenyl diazonium salt is coupled with 1-amino-2-naphthol at pH <= 6. Which product will be present in the highest percentage in the product mixture?

1. (A) 1-amino-2-naphthol coupled with p-nitrophenyl diazonium at the 1-position of the naphthalene ring
2. (B) p-nitrophenyl azo compound coupled to 1-amino-2-naphthol through the benzene ring
3. (C) 1-amino-2-naphthol coupled with p-nitrophenyl diazonium at the 3-position of the naphthalene ring
4. (D) p-nitrophenyl azo compound coupled to 1-amino-2-naphthol through the naphthalene ring

Correct answer: (C) 1-amino-2-naphthol coupled with p-nitrophenyl diazonium at the 3-position of the naphthalene ring

Solution

At pH <= 6, the -NH2 group is protonated (-NH3+) and cannot activate the ring. The -OH group at C2 remains phenolic and activates positions C1 and C3 for electrophilic substitution. Since C1 is occupied by -NH2, coupling with the diazonium salt occurs preferentially at C3.

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