Which position of phenol is involved in coupling reaction with benzene diazonium chloride?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → para
In a coupling reaction the benzenediazonium ion acts as an electrophile and attacks an activated aromatic ring, joining the two rings through an –N=N– bond. The diazonium ion is a weak electrophile, so it reacts only with strongly activated rings such as phenol (as the phenoxide ion, in mildly alkaline solution) and aniline. The –OH group directs the attack to the ortho and para positions, and the bulky diazonium ion goes to the less crowded para position:
\( \displaystyle \ce{C6H5N2^+Cl^- + C6H5OH} \xrightarrow{\ce{OH^-}} \ce{C6H5-N=N-C6H4OH} + \ce{Cl^- + H2O} \)
Why the other options are incorrect
Option (1) ortho — Incorrect. The ortho positions are activated too, but they are crowded by the –OH group; coupling takes place there only when the para position is already occupied.
Option (2) meta — Incorrect. The –OH group raises the electron density at the ortho and para positions, not at meta, so the weak electrophile does not attack there.
NCERT (2026-27 edition):
Reactions Involving Retention of Diazo Group
