Indian Forest Service (Mains), Chemistry optional · 2025 · Paper II
Q1(e). Oxymercuration of norbornene
Question
Predict the oxymercuration–demercuration product of the drawn norbornene and explain its stereochemistry. [structure of norbornene given in the paper]
Answer in brief
Under aqueous oxymercuration conditions, the main alcohol is exo-2-norborneol.
Key points
- The bridge hinders endo-face approach, so electrophilic Hg(OAc)⁺ addition occurs preferentially from the accessible exo face.
- The bridged intermediate undergoes characteristic cis-exo addition of Hg and OH; water capture and deprotonation give the exo organomercury alcohol.
- NaBH₄ replaces the C–Hg group by C–H; this demercuration step is radical in character and not generally stereospecific.
- The diagnostic retained stereochemistry is the predominantly exo OH group; no methyl shift or skeletal rearrangement is required.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
Coversoxymercuration–demercurationnorborneneexo-2-norborneolexo face selectivityMarkovnikov hydration
All parts of Question 1
- 1(a) Aromaticity of small rings5 marks
- 1(b) Nitrene transfer to an alkene5 marks
- 1(c) Electrophilic substitution of heteroarenes5 marks
- 1(d) Elimination next to an existing alkene5 marks
- 1(e) Oxymercuration of norbornene5 marks
- 1(f) Medium-dependent pinacol rearrangement5 marks
- 1(g) Two thermal electrocyclic steps5 marks
- 1(h) Intramolecular Claisen condensation5 marks