Q10(b). 4π ring opening, then 6π ring closure: the intermediate II
Predict the intermediate II in the following electrocyclic reaction which involves 4π and 6π electron system: I → (Δ) → II → (Δ) → III. Propose mechanism with suitable explanation. [Structures of I and III given in the paper]
Answer in brief
II = cis,cis,trans-cyclodeca-1,3,5-triene, (1Z,3Z,5E), C₁₀H₁₄. I → II: thermal 4π conrotatory ring opening. II → III: thermal 6π disrotatory ring closure.
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.
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.
Topic notes: pericyclic reactions, with every Civil Services, IFoS and Geo-Scientist PYQ →
Coverselectrocyclic reactionconrotatorydisrotatoryWoodward–Hoffmann rulescyclodecatriene
All parts of Question 10
- 10(a) Perkin reaction, then three steps to 2-methylindane10 marks
- 10(b) 4π ring opening, then 6π ring closure: the intermediate II5 marks
- 10(c) Cope rearrangement of cis-2,3-divinyloxirane5 marks
- 10(d) Structure from mass, IR and NMR spectra: a bromo acid10 marks