UPSC Civil Services (Mains), Chemistry optional · 2022 · Paper II

Q2(b)(ii). 1,2-Dihydronaphthalene with NBS, then sodium ethoxide

5 marks
Topic: Reactive intermediates
Question only

Question

Predict [A] and [B] in the following reaction: 1,2-dihydronaphthalene with NBS in CCl₄ gives [A]; [A] with NaOEt in EtOH, Δ gives [B]. [structure of the substrate 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 2 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: reactive intermediates (carbocations, carbanions, radicals, carbenes, nitrenes, benzyne), with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversNBSallylic brominationWohl–Ziegler reactiondehydrohalogenationaromatisation

All parts of Question 2

2(a) Products X and Y in three reactions15 marks
2(b)(i) 2,2-Dimethyltetrahydrofuran with one equivalent of HI5 marks
2(b)(ii) 1,2-Dihydronaphthalene with NBS, then sodium ethoxide5 marks
2(b)(iii) Alkenes from 2-chloro-2,3-dimethylpentane with sodium ethoxide5 marks
2(c)(i) Matching three heterocycle syntheses; mechanism of the indole synthesis10 marks
2(c)(ii) L-Dopa from L-tyrosine10 marks