JEE Main 2021 · 1 September · evening · Single correct · +4 / −1
Which one of the following gives the most stable Diazonium salt?
- (a) CH₃-CH₂-CH₂-NH₂
- (b)
- (c)
- (d) CH₃; |; CH₃-, C, -NH₂; |; H
Answer and solution
Answer (b)
Solution
Chemistry ma’am · 3 steps
A stable diazonium salt needs an -NH₂ group sitting directly on a benzene ring. Find that one.
- Why aryl wins. In ArN₂⁺ the benzene ring's π electrons spread the positive charge over the ring by resonance. That is why arenediazonium salts survive in cold solution at 273 to 278 K.
- Two conditions. The amine must be primary, so that it has two N–H bonds to lose during diazotisation. It must also be aromatic, so that a ring is there to stabilise the charge.
Option Type of amine With NaNO₂ + HCl in the cold (a) CH₃CH₂CH₂NH₂ primary aliphatic diazonium ion forms but loses N₂ at once, giving alcohols (b) 4-methylaniline primary aromatic stable arenediazonium salt (c) N-methylaniline secondary aromatic N-nitrosoamine, no diazonium salt (d) (CH₃)₂CHNH₂ primary aliphatic diazonium ion forms but loses N₂ at once - So. Only 4-methylaniline is a primary aromatic amine, so (b) gives the most stable diazonium salt. The para methyl group also pushes electron density into the ring, which helps a little more.
The idea to keep. A stable diazonium salt needs a primary -NH₂ attached directly to an aromatic ring. Aliphatic diazonium ions lose N₂ instantly, and secondary amines give nitrosoamines instead.
Answer from the NTA final answer key. Solution by PrepWiser.