Q8(d). Photochemical 6π electrocyclic ring closure of an octatriene
Predict the structure of the product including stereochemical aspects based on orbital symmetry principles for the following reaction: [octatriene under hν; structure given in the paper]
Model answer
The free solution for 2022 answers questions 1, 4, 5, 6, 7 and 10, the ones picked in its time plan. Question 8 is answered in full in the Geo-Scientist Chemistry Paper III, 2021 to 2025 book, with every part of every paper.
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UPSC Combined Geo-Scientist (Main) Chemistry Paper III: Model Answers 2021 to 2025
- All ten questions of each paper, with the question printed above its answer
- Instruments drawn as labelled diagrams, numericals worked with units
- Topic-wise weightage and a topic-wise index
Topic notes: pericyclic reactions, with every Civil Services, IFoS and Geo-Scientist PYQ →
Coverselectrocyclic reactionconrotatoryphotochemical ring closureoctatrienedimethylcyclohexadiene
All parts of Question 8
- 8(a) Woodward–Fieser rules: λmax of three unsaturated ketones10 marks
- 8(b) ¹H NMR of an enaminone: assignment and the change at 300 MHz5 marks
- 8(c) A diene and an enone in UV light: [2 + 2] cycloaddition5 marks
- 8(d) Photochemical 6π electrocyclic ring closure of an octatriene5 marks
- 8(e) Cope rearrangement of a 1,5-diene with CN and CO₂Et5 marks