UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper II
Q1(e)(i). 2-Chloro-6-methylcyclohexanone with methoxide
Question
Identify the major product of the reaction of 2-chloro-6-methylcyclohexanone with methoxide. [reaction and options (A)–(D) given in the paper]
Answer in brief
(A), methyl 1-methylcyclopentane-1-carboxylate, formed by the Favorskii rearrangement (ring contraction).
Key points
- Favorskii: α′-H removed; enolate displaces Cl⁻ internally: cyclopropanone.
- MeO⁻ adds to C=O; ring opens to the more stable (2°) carbanion.
- Rejected: (B) needs 3° carbanion; (C) SN2, (D) E2 do not compete.
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.
Topic notes: molecular rearrangements, with every Civil Services, IFoS and Geo-Scientist PYQ →
CoversFavorskii rearrangementcyclopropanone intermediatering contractionα-haloketonemethoxide
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