Indian Forest Service (Mains), Chemistry optional · 2024 · Paper II
Q1(h). Hydrazine reductions
Question
Give products from (i) CH₃CHBrCH₂COCH₃ with hydrazine/t-BuOK in hot DMSO and (ii) RCOCOR with hydrazine and alcoholic KOH/glycol.
Answer in brief
(i) 1,2-Dimethylcyclopropane; (ii) under exhaustive Wolff–Kishner conditions, RCH₂CH₂R.
Key points
- (i) Condensation gives the ketone hydrazone; cyclization chemistry of the β-halo substrate can proceed through a pyrazoline, and nitrogen extrusion closes the three-carbon ring.
- Equivalently, the carbanion generated during reductive loss of nitrogen attacks the β-carbon intramolecularly, displacing Br⁻.
- (ii) Each carbonyl undergoes hydrazone formation, base-mediated proton transfers and N₂ loss. Protonation replaces each C=O with CH₂.
- Benzil, for example, is converted to bibenzyl under exhaustive hydrazine/KOH/glycol reduction.
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.
CoversWolff-Kishner reductionhydrazonecyclopropane formation1,2-diketone reductionHuang-Minlon modification
All parts of Question 1
- 1(a) Annulenes and aromaticity5 marks
- 1(b) Secondary kinetic isotope effect5 marks
- 1(c) Five aromaticity decisions5 marks
- 1(d) Amination through a benzyne5 marks
- 1(e) Intramolecular aldol condensation5 marks
- 1(f) Pulegone to a ring-contracted ester5 marks
- 1(g) Photochemical alkyl migration5 marks
- 1(h) Hydrazine reductions5 marks