Q2(a). Ester shift with sodium ethoxide; cyclisation of an epoxy-diene
(i) In the presence of sodium ethoxide (1) NaOEt; 2) HCl), the following transformation occurs. Explain. (ii) Propose a suitable mechanism for the following transformation (H₂SO₄, H₂O). [structures of the cyclic β-keto ester and the epoxy-diene given in the paper]
Model answer
The free solution for 2025 answers questions 1, 3, 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.
Part of VKC Basic
Read the key points and the full model answer with VKC Basic
VKC Basic (₹999 for 6 months) opens every solved answer, the notes, the handbook and the daily answer archive. Every Mains test series includes it.
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
CoversDieckmann condensationretro-Claisenβ-keto esterepoxide openingcationic cyclisation
All parts of Question 2
- 2(a) Ester shift with sodium ethoxide; cyclisation of an epoxy-diene15 marks
- 2(b)(i) Acid-catalysed hydration of 3,3-dimethylbut-1-ene10 marks
- 2(b)(ii) Styrene with BrCCl₃ under light5 marks
- 2(c) Products of four reactions20 marks