UPSC Combined Geo-Scientist, Mains · 2026 · Mains Paper III
Q9(b). Ionone mass spectrum; HWE, DIBAL-H and Sharpless sequence
Question
(i) Among the following, identify the ionone that will give the peak at m/z=136 in EI mass spectrum and explain your answer: α-ionone, β-ionone. (ii) Draw the major products (A–C) formed (with appropriate stereochemistry, if any) in the following reaction sequence: PhCHO + (MeO)₂P(O)CH₂CO₂Me, NaH, THF → A; DIBAL-H (2 equiv.), THF → B; Ti(OⁱPr)₄, (+)-DET, t-BuOOH → C.
Model answer
The free solution for 2026 answers the questions picked in its time plan. Question 9 is answered in full in the Book Edition of the 2026 solutions of Geo-Scientist Chemistry Paper III.
Coversretro-Diels–Alder; asymmetric synthesisIonone mass spectrumHWE
All parts of Question 9
- 9(a) Diels–Alder of a quinone; ring opening and cycloaddition of a cyclobutene10 marks
- 9(b) Ionone mass spectrum; HWE, DIBAL-H and Sharpless sequence10 marks
- 9(c) Ziegler–Natta polymerisation of ethylene10 marks