UPSC Combined Geo-Scientist
Chemist
- 3 descriptive papers
- 200 marks each
- 3 h per paper
Mains Paper III covers analytical and organic chemistry.
All years
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Mains Paper III, analytical and organic chemistry
Question paper, 2025
UPSC Combined Geo-Scientist, Stage II (Mains). 11 pages, as issued by UPSC.
Every question of 2025, one page each53 parts in 10 questions, with the question as text and the key points of its answer
Question 1 40 marks
- 1(a)Sample mass for a sampling standard deviation of ±5 %5 marks
- 1(b)van Deemter equation and its significance5 marks
- 1(c)Non-absorbing analyte by UV-vis spectrophotometry5 marks
- 1(d)Flame absorption profiles of magnesium and silver5 marks
- 1(e)Heating rate, particle size and heat of reaction in TGA5 marks
- 1(f)Quadrupole mass analyser in ICP–MS5 marks
- 1(g)Gravimetric estimation of nickel in steel5 marks
- 1(h)Lattice spacing from Bragg’s law5 marks
Question 2 30 marks
Question 3 30 marks
Question 4 30 marks
Question 5 30 marks
Question 6 40 marks
- 6(a)Singlet and triplet carbenes; fluorenylidene with cis-but-2-ene4 marks
- 6(b)Bromine addition: styrene reacts faster than propene4 marks
- 6(c)Addition of HCl to an α,β-unsaturated acid4 marks
- 6(d)Michael addition of a cyclic 1,3-dione to cyclohex-2-enone4 marks
- 6(e)Hydroboration–oxidation of 1-methylcyclohexene4 marks
- 6(f)Cope rearrangement of a 1,5-diene4 marks
- 6(g)Diels–Alder reaction: product and reactants4 marks
- 6(h)IR distinction: hydrogen bonding and ring strain4 marks
- 6(i)McLafferty rearrangement: 2-pentanone and 3-pentanone4 marks
- 6(j)NMR assignment of 4-methylpent-1-yne4 marks
Question 7 30 marks
- 7(a)(i)p-Cresol: Reimer–Tiemann reaction, then a cyanohydrin5 marks
- 7(a)(ii)2-Naphthoic acid to a urethane: Curtius rearrangement5 marks
- 7(b)(i)6π electrocyclic ring closure: thermal and photochemical modes5 marks
- 7(b)(ii)Furil to furilic acid: benzilic acid rearrangement5 marks
- 7(c)(i)4-Methoxybenzaldehyde with NaCN: benzoin condensation5 marks
- 7(c)(ii)Norrish Type II against Type I in two ketones5 marks
Question 8 30 marks
- 8(a)(i)6,6-Dimethylfulvene takes up hydride; a simple alkene does not5 marks
- 8(a)(ii)Doped and non-doped conducting polymers; polyacetylene5 marks
- 8(b)(i)Wittig alkene, then epoxide and diol5 marks
- 8(b)(ii)Ozonolysis, then intramolecular aldol condensation5 marks
- 8(c)(i)[1,5]-Hydrogen shift, then ring opening of a cyclobutene5 marks
- 8(c)(ii)Oxy-Cope rearrangement of a bicyclic vinyl carbinol5 marks
Question 9 30 marks
- 9(a)(i)Dieckmann condensation, then NaBH₄ reduction5 marks
- 9(a)(ii)Polyurethane: characteristic use and repeating unit5 marks
- 9(b)(i)HBr and buta-1,3-diene: kinetic and thermodynamic control5 marks
- 9(b)(ii)Sharpless asymmetric epoxidation of an allylic alcohol5 marks
- 9(c)Structure from IR, NMR and mass spectra: C₁₀H₁₃NO₂10 marks
Question 10 30 marks
- 10(a)(i)para-Claisen rearrangement of an allyl aryl ether5 marks
- 10(a)(ii)Electrocyclic ring closure and Diels–Alder cycloaddition5 marks
- 10(b)(i)Woodward–Fieser rules: two ketones, 249 nm and 287 nm5 marks
- 10(b)(ii)Structure from IR bands and two chemical tests: M = 1085 marks
- 10(c)(i)Structure from IR, ¹H and ¹³C NMR: C₉H₈O₂5 marks
- 10(c)(ii)Mass spectrum: benzyl acetate or ethyl benzoate5 marks