UPSC Combined Geo-Scientist, Mains · 2024 · Mains Paper III

Q6(e). Intramolecular oxymercuration–demercuration: a cyclic ether

4 marks
Topic: Addition reactions
Answered

Question

Give the product and mechanism of the following reaction: 4-methylpent-4-en-1-ol, (i) Hg(OAc)₂/THF, (ii) NaBH₄/MeOH → ? [structure given in the paper]

Answer in brief

2,2-Dimethyltetrahydrofuran (2,2-dimethyloxolane), C₆H₁₂O: the OH group of the same molecule adds to the C=C in the Markovnikov sense.

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Topic notes: addition to alkenes and alkynes (Markovnikov, stereochemistry, dienes), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversoxymercurationdemercurationmercurinium ionMarkovnikov additioncyclic ethertetrahydrofuran

All parts of Question 6

6(a) Curtius rearrangement; the isocyanate closes to a cyclic urea4 marks
6(b) HBr and a conjugated diene: 1,2- and 1,4-addition4 marks
6(c) Phenylglycine and mandelic acid from benzaldehyde4 marks
6(d) Coumarin and 3-acetylcoumarin from salicylaldehyde4 marks
6(e) Intramolecular oxymercuration–demercuration: a cyclic ether4 marks
6(f) trans- and cis-Cyclohexane-1,2-diol from cyclohexanone4 marks
6(g) [1,5]-Carbon shift and Cope rearrangement4 marks
6(h) Four C₁₀H₁₄ isomers: the one marked by a McLafferty peak4 marks
6(i) C₃H₇NO with two N–methyl singlets: N,N-dimethylformamide4 marks
6(j) ν(C=C) of methylidenecycloalkanes and ring size4 marks