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 years
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Paper II, organic chemistry and spectroscopy
Question paper, 2023
UPSC Civil Services (Mains), Chemistry optional. 16 pages, as issued by UPSC.
Every question of 2023, one page each50 parts in 8 questions, with the question as text and the key points of its answer
Question 1 50 marks
- 1(a)(i)Acidity of cyclopentadiene5 marks
- 1(a)(ii)Hydrogen exchange in cyclopropyl and cyclopropenyl ketones5 marks
- 1(b)(i)IUPAC name with stereodescriptors5 marks
- 1(b)(ii)Dimerisation ability of three triarylmethyl-type radicals5 marks
- 1(c)Methyl iodide with sodium azide: DMF against methanol10 marks
- 1(d)Photochemical electrocyclic closure of two cyclonona-1,3-dienes10 marks
- 1(e)(i)2-Chloro-6-methylcyclohexanone with methoxide5 marks
- 1(e)(ii)Name reaction that gives nitrogen as a by-product5 marks
Question 2 50 marks
- 2(a)(i)Aromatic, antiaromatic or non-aromatic by the Hückel rule5 marks
- 2(a)(ii)Primary and secondary kinetic isotope effects5 marks
- 2(a)(iii)Enolates of butan-2-one: NaOMe versus LDA5 marks
- 2(b)(i)Hydrolysis of bis(2-chloroethyl) sulfide and of 1,5-dichloropentane5 marks
- 2(b)(ii)Both glycosyl bromides give the β-glycoside5 marks
- 2(b)(iii)Ketene, hν, then cis-but-2-ene10 marks
- 2(c)(i)Acetolysis of 2-(cyclopent-3-enyl)ethyl tosylate10 marks
- 2(c)(ii)Indole: electrophilic substitution at C-3, not C-25 marks
Question 3 50 marks
Question 4 50 marks
- 4(a)(i)Norbornene with D–Br5 marks
- 4(a)(ii)Relative rates of bromination in methanol5 marks
- 4(a)(iii)Hydroboration–oxidation of a tetrasubstituted alkene10 marks
- 4(b)Cyclic benzylammonium salt with NaNH₂ / NH₃10 marks
- 4(c)(i)Crossed aldol: butanone and acetaldehyde10 marks
- 4(c)(ii)Benzonitrile from benzene10 marks
Question 5 50 marks
- 5(a)Number of ¹H NMR signals in (A) and (B)10 marks
- 5(b)C=C stretch of methylenecyclopropane and methylenecyclobutane10 marks
- 5(c)Acetylene to neoprene; why rubber perishes in air10 marks
- 5(d)LiAlH₄ reduction of camphor: OH cis to the bridge10 marks
- 5(e)Photolysis of acetone: vapour phase and room temperature10 marks
Question 6 50 marks
- 6(a)(i)Energy change of HCl + D₂ → DCl + HD10 marks
- 6(a)(ii)C=O bands of butyric acid, its ethyl ester and its anhydride5 marks
- 6(b)(i)Products A, B and C10 marks
- 6(b)(ii)Tacticity: isotactic, syndiotactic and atactic polymers5 marks
- 6(c)(i)Structure of C₁₆H₂₅NO from IR and ¹H NMR10 marks
- 6(c)(ii)Order of chemical shift of the lettered protons10 marks
Question 7 50 marks
- 7(a)2′-Deoxycytidine-3′-monophosphate; acidity; duplex stability; G≡C pairing15 marks
- 7(b)(i)Vapour-phase photolysis of cyclopentanone10 marks
- 7(b)(ii)Direct and benzophenone-sensitised photolysis of 1,3-butadiene5 marks
- 7(c)(i)Structures of (A), (B), (C), (D) and (E)10 marks
- 7(c)(ii)Osmate ester from cyclohexene; oxidation state and geometry of osmium5 marks
- 7(c)(iii)D-Mannitol: cyclohexylidene ketal, then HIO₄5 marks
Question 8 50 marks
- 8(a)(i)Doxepin: site of ionisation, m/z 58 ion and metastable ion10 marks
- 8(a)(ii)Ketone C₇H₁₂O with λmax = 249 nm5 marks
- 8(b)(i)Microwave activity; rotational constants of CO10 marks
- 8(b)(ii)Expected J(Ha–Hb) in three alkenes5 marks
- 8(c)(i)Keto and enol percentages of acetylacetone from integration10 marks
- 8(c)(ii)Two isomeric amides C₅H₁₁NO by mass spectrometry5 marks
- 8(c)(iii)Fundamental vibrations of CO₂ and their IR activity5 marks