UPSC Civil Services (Mains), Chemistry optional · 2025 · Paper II

Q4(c)(ii). Kinetic and thermodynamic enolates trapped with D₂O

10 marks
Topic: Reaction mechanisms
Question only

Question

Identify the major product in the following reactions and justify your answer: the ketone with 1) LDA/THF, 2) D₂O gives Q; the same ketone with 1) excess NaOH, 2) D₂O gives P. [structure of the ketone given in the paper]

Model answer

The free solution for 2025 answers questions 1, 3, 5, 6 and 8, the ones picked in its time plan. Question 4 is answered in full in the Chemistry Paper II, 2021 to 2025 book, with every part of every paper.

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UPSC Civil Services (Main) Chemistry Paper II: Model Answers 2021 to 2025

All eight questions of each paper, with the question printed above its answer
Mechanisms drawn out and labelled on the scheme
Topic-wise weightage and a topic-wise index

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Topic notes: methods of studying mechanisms (isotopic labelling, crossover, trapping, kinetic isotope effect, kinetic and thermodynamic control), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverskinetic enolatethermodynamic enolateLDAdeuterium exchangeD2O

All parts of Question 4

4(a)(i) Molecular weight of poly(p-hydroxybenzoic acid)7 marks
4(a)(ii) Structure of the polymer3 marks
4(a)(iii) Precursor of natural rubber5 marks
4(b)(i) Nylon 6 and nylon 6,6 compared5 marks
4(b)(ii) Preparing syndiotactic polystyrene5 marks
4(b)(iii) Salient features of the α-helix5 marks
4(c)(i) Two dichlorides with NaN₃: neighbouring sulfur10 marks
4(c)(ii) Kinetic and thermodynamic enolates trapped with D₂O10 marks