UPSC Civil Services (Mains)
Chemistry optional
- 2 papers
- 250 marks each
- 3 h per paper
- 5 of 8 questions, Q1 and Q5 compulsory
Paper II covers organic chemistry and spectroscopy.
All topics
Paper II, organic chemistry and spectroscopy
Pericyclic reactions: every question, 2021 to 2025
19 parts worth 185 marks have been set on this unit in UPSC CSE Chemistry Paper II from 2021 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
Syllabus
Classification and examples; Woodward-Hoffmann rules: electrocyclic reactions, cycloaddition reactions [2+2 and 4+2] and sigmatropic shifts [1, 3; 3, 3 and 1, 5], FMO approach.
Notes: Pericyclic reactions (full notes) · short notes
2025
- Q5(a) Dichloroacetyl chloride with Et₃N, then cyclopentadiene10 marks Answered
- Q7(b)(i) Diels–Alder reactivity of four dienes10 marks Question only
- Q7(b)(ii) 2-Methoxybutadiene with acrylonitrile5 marks Question only
- Q7(c)(i) Rearrangement of a cis-divinylcyclopropane10 marks Question only
- Q7(c)(ii) Mode of ring closure in two electrocyclic reactions10 marks Question only
2024
- Q1(e) Electrocyclic steps of cyclononatriene10 marks Answered
- Q3(b)(i) Enone from a methoxy triene5 marks Answered
- Q3(b)(ii) Classify the rearrangement at 33 °C5 marks Answered
- Q3(b)(iii) Methoxy methyl benzoquinone with butadiene5 marks Answered
2023
- Q1(d) Photochemical electrocyclic closure of two cyclonona-1,3-dienes10 marks Answered
- Q3(a) Cycloocta-1,4-diene to a tricyclic isomer: heat or light15 marks Answered
- Q3(b) 3-Phenyl-4-pentenal from 3-(cinnamyloxy)acrylic acid15 marks Answered
- Q3(d) Methoxybutadienes with acrolein10 marks Answered
2022
- Q1(e) Heating cyclopentadiene10 marks Answered
- Q3(a) Acetal and ortho-ester Claisen rearrangements of an allylic alcohol15 marks Question only
- Q3(b)(i) Ergosterol, precalciferol and the need for sunlight10 marks Question only
2021
- Q1(e) Two transformations by electrocyclic relays10 marks Answered
- Q4(a)(i) Deuterium scrambling on heating 3-deuteroindene10 marks Question only
- Q4(a)(ii) Cyclopentadiene with maleic anhydride10 marks Question only
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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