Q3(b)(i). Ergosterol, precalciferol and the need for sunlight
Considering the structural features of ergosterol (A) and precalciferol (B), a precursor of vitamin D, giving mechanistic details, explain why vitamin D deficiency is endemic in those parts of the world where sunlight is scarce. [structures of A and B given in the paper]
Model answer
The free solution for 2022 answers questions 1, 4, 5, 6 and 8, the ones picked in its time plan. Question 3 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
Topic notes: pericyclic reactions, with every Civil Services, IFoS and Geo-Scientist PYQ →
Coversergosterolprevitamin Delectrocyclic ring openingWoodward–Hoffmann rulesconrotatoryvitamin D
All parts of Question 3
- 3(a) Acetal and ortho-ester Claisen rearrangements of an allylic alcohol15 marks
- 3(b)(i) Ergosterol, precalciferol and the need for sunlight10 marks
- 3(b)(ii) p-Bromonitrobenzene to m-bromobenzoic acid5 marks
- 3(c)(i) Cl₂CH–CF₃ with ethoxide: product and energy profile10 marks
- 3(c)(ii) SN2 reactivity of four tertiary bromides10 marks