UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper II
Q1(e)(ii). Name reaction that gives nitrogen as a by-product
Question
Identify the name reaction which produces nitrogen as a by-product. (A) Fischer indole synthesis (B) von Richter reaction (C) Stobbe reaction (D) Bischler–Napieralski reaction
Answer in brief
(B) von Richter reaction.
Key points
- Cine substitution: CO₂H enters ortho to the carbon NO₂ leaves.
- Nitro N and cyanide N leave together as N₂; no nitrite forms.
- Example: p-bromonitrobenzene with KCN in aq. EtOH gives m-bromobenzoic acid + N₂.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
Coversvon Richter reactioncine substitutionFischer indole synthesisStobbe condensationBischler–Napieralski reaction
All parts of Question 1
- 1(a)(i) Acidity of cyclopentadiene5 marks
- 1(a)(ii) Hydrogen exchange in cyclopropyl and cyclopropenyl ketones5 marks
- 1(b)(i) IUPAC name with stereodescriptors5 marks
- 1(b)(ii) Dimerisation ability of three triarylmethyl-type radicals5 marks
- 1(c) Methyl iodide with sodium azide: DMF against methanol10 marks
- 1(d) Photochemical electrocyclic closure of two cyclonona-1,3-dienes10 marks
- 1(e)(i) 2-Chloro-6-methylcyclohexanone with methoxide5 marks
- 1(e)(ii) Name reaction that gives nitrogen as a by-product5 marks