JEE Main 2023 · 12 April · morning · Single correct · +4 / −1
The incorrect statement regarding the reaction given below is
- (a) 'B' is N-nitroso ammonium compound
- (b) The product 'B' formed in the above reaction is p-nitroso compound at low temperature
- (c) The electrophile involved in the reaction is NO⁺
- (d) The reaction occurs at low temperature
Answer and solution
Answer (a) 'B' is N-nitroso ammonium compound
Solution
Chemistry ma’am · 4 steps
A tertiary aryl amine has no N–H to lose, so NO⁺ attacks the ring at para, not the nitrogen.
- Make the electrophile. Cold NaNO₂ and HX give HNO₂, which forms the nitrosonium ion NO⁺. The mixture is kept near 0 to 5 °C because nitrous acid decomposes on warming.
- Why not nitrogen. A secondary amine loses its N–H proton after NO⁺ attacks and becomes a neutral N-nitrosamine. In N,N-dimethylaniline the nitrogen has no H, so no stable N-nitroso product can form.
- Ring attack instead. The -N(CH₃)₂ group strongly activates the ring and directs ortho and para. The bulky group blocks ortho, so NO⁺ substitutes at para and gives p-nitroso-N,N-dimethylaniline as B.
Statement Check Verdict (a) B is an N-nitroso ammonium compound Substitution happens on the ring, not on N Incorrect (b) B is a p-nitroso compound Para ring substitution Correct (c) Electrophile is NO⁺ Formed from HNO₂ in acid Correct (d) Reaction at low temperature HNO₂ is unstable when warm Correct - So. The incorrect statement is (a). B is a C-nitroso compound, p-nitroso-N,N-dimethylaniline, not an N-nitroso ammonium compound.
The idea to keep. With nitrous acid, 1° amines give diazonium salts or alcohols, 2° amines give N-nitrosamines, and 3° aryl amines get ring nitrosation at para. Count the N–H bonds first.
Answer from the NTA final answer key. Solution by PrepWiser.