Q7(b). LiAlH₄ and NaBH₄: solvents, reactivity and choice of reagent
Discuss the solvent compatibility of LiAlH₄ and NaBH₄ and the factors responsible for their differential reactivity. Also suggest the preferred reagent between the two for the two given transformations (a keto amide in which only the COCH₃ group is to be reduced, and a propargylic alcohol to be reduced). [schemes given in the paper]
Model answer
The free solution for 2021 answers questions 1, 2, 3, 5 and 8, the ones picked in its time plan. Question 7 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
CoversLiAlH4NaBH4chemoselective reductionhydride reagentssolvent compatibility
All parts of Question 7
- 7(a) A, B and C in two polymer-forming sequences20 marks
- 7(b) LiAlH₄ and NaBH₄: solvents, reactivity and choice of reagent15 marks
- 7(c) Structure of a phenol C₁₀H₁₄O from IR, mass and NMR data15 marks