Which of the following cannot be prepared by Sandmeyer reaction ?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → ArF
In the Sandmeyer reaction, the diazonium group of an arenediazonium salt is replaced by a nucleophile with the help of a copper(I) salt, and nitrogen gas escapes. It works for Cl, Br and CN:
\( \displaystyle \ce{ArN2^+X^-} \xrightarrow{\ce{Cu2Cl2/HCl}} \ce{ArCl + N2} \)
Fluorine cannot be introduced this way. Aryl fluorides are made by the Balz–Schiemann reaction: the diazonium salt is converted to the diazonium fluoroborate with fluoroboric acid, and this salt is heated.
Option (1) ArCl — Prepared by the Sandmeyer reaction. With Cu2Cl2/HCl, as shown above.
Option (2) ArBr — Prepared by the Sandmeyer reaction. With Cu2Br2/HBr.
Option (3) ArF — Not prepared by it. Aryl fluorides are made through the diazonium fluoroborate.
Option (4) ArCN — Prepared by the Sandmeyer reaction. With CuCN/KCN.
NCERT (2026-27 edition):
Reactions Involving Displacement of Nitrogen – …
