In the following reactions, which one is NOT correct?

Solution

Chemistry ma’am · 3 steps

Ethanol is not a nucleophile here: it hands a hydride to the diazonium salt and gives benzene, not an ether.

1. The common pattern. In every reaction, the -N₂⁺ group leaves as nitrogen gas. Whatever the reagent supplies takes its place on the ring. So check what each reagent actually supplies.
2. Role of ethanol. Mild reducing agents such as H₃PO₂ and ethanol both replace -N₂⁺ by -H. Ethanol is oxidised to ethanal in the process, so the main product is benzene.

   C₆H₅N₂⁺Cl⁻ + CH₃CH₂OH → C₆H₆ + N₂ + CH₃CHO + HCl

   Option	Reagent	Group that replaces -N₂⁺	Product shown
   (a)	H₃PO₂ / H₂O	-H (reduction)	benzene, correct
   (b)	CuCN / KCN	-CN (Sandmeyer)	benzonitrile, correct
   (c)	C₂H₅OH	-H (reduction)	ethoxybenzene, not correct
   (d)	KI	-I	iodobenzene, correct

3. So. The reaction in (c) should give benzene, not ethoxybenzene (phenetole). Option (c) is the incorrect one.

The idea to keep. Remember the pair H₃PO₂ and ethanol together. Both reduce ArN₂⁺ to ArH. This is how you remove an -NH₂ group from a ring after it has done its directing job.

Answer from the NTA final answer key. Solution by PrepWiser.