Q10(b)(i). Woodward–Fieser rules: two ketones, 249 nm and 287 nm
Two ketones were filled in two reagent bottles A and B, but their labels got damaged and were removed. Measurement of UV spectra of the contents of the two bottles gave λmax 249 nm for A and 287 nm for B. Assign the structures with appropriate λmax for A and B by using Woodward–Fieser rule. [structures (I) and (II) given in the paper]
Model answer
The free solution for 2025 answers questions 1, 2, 4, 6, 7 and 9, the ones picked in its time plan. Question 10 is answered in full in the Geo-Scientist Chemistry Paper III, 2021 to 2025 book, with every part of every paper.
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UPSC Combined Geo-Scientist (Main) Chemistry Paper III: Model Answers 2021 to 2025
- All ten questions of each paper, with the question printed above its answer
- Instruments drawn as labelled diagrams, numericals worked with units
- Topic-wise weightage and a topic-wise index
CoversWoodward-Fieser rulesλmax calculationα,β-unsaturated ketoneUV spectroscopyenone
All parts of Question 10
- 10(a)(i) para-Claisen rearrangement of an allyl aryl ether5 marks
- 10(a)(ii) Electrocyclic ring closure and Diels–Alder cycloaddition5 marks
- 10(b)(i) Woodward–Fieser rules: two ketones, 249 nm and 287 nm5 marks
- 10(b)(ii) Structure from IR bands and two chemical tests: M = 1085 marks
- 10(c)(i) Structure from IR, ¹H and ¹³C NMR: C₉H₈O₂5 marks
- 10(c)(ii) Mass spectrum: benzyl acetate or ethyl benzoate5 marks