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.
Spectroscopy: every question, 2021 to 2025
54 parts worth 475 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.
Principle and applications in structure elucidation: (i) Rotational: diatomic molecules; isotopic substitution and rotational constants. (ii) Vibrational: diatomic molecules, linear triatomic molecules, specific frequencies of functional groups in polyatomic molecules. (iii) Electronic: singlet and triplet states; n→π* and π→π* transitions; application to conjugated double bonds and conjugated carbonyls, Woodward-Fieser rules; charge transfer spectra. (iv) Nuclear magnetic resonance (¹H NMR): basic principle; chemical shift and spin-spin interaction and coupling constants. (v) Mass spectrometry: parent peak, base peak, metastable peak, McLafferty rearrangement.
Explained on the blog: Woodward–Fieser rules: calculating λmax of enones and dienes (asked every year from 2022 to 2025)
Notes: UV spectroscopy and Woodward–Fieser rules (full notes) · short notes
Notes: Structure from combined spectra: IR, NMR and mass (full notes) · short notes
Notes: Rotational (microwave) and Raman spectra (full notes) · short notes
Notes: Vibrational and electronic spectra: anharmonicity and Franck–Condon (full notes) · short notes
Notes: Infrared spectroscopy: group frequencies, carbonyl stretching and hydrogen bonding (full notes) · short notes
Notes: ¹H and ¹³C NMR: chemical shift, spin–spin coupling and coupling constants (full notes) · short notes
Notes: Mass spectrometry: molecular ion, metastable peak and McLafferty rearrangement (full notes) · short notes
2025
- Q5(d) Rotational spectroscopy10 marks Answered
- Q5(e) NMR at two field strengths; mass spectrum of a ketone10 marks Answered
- Q6(b) Three numericals15 marks Answered
- Q7(a)(i) Two UV bands of acetone5 marks Question only
- Q7(a)(ii) λmax by the Woodward–Fieser rules10 marks Question only
- Q8(a)(i) Coupling constants of the lettered protons5 marks Answered
- Q8(a)(ii) Chemical shifts of Hᵃ and Hᵇ5 marks Answered
- Q8(a)(iii) Number of ¹H NMR signals5 marks Answered
- Q8(b)(i) Structure of the halogenated ester10 marks Answered
- Q8(b)(ii) C₆H₁₂ alkenes with peaks at m/z 42 and 565 marks Answered
- Q8(c)(i) Characteristic fragment ions10 marks Answered
- Q8(c)(ii) Structure of C₄H₅NO₂10 marks Answered
2024
- Q5(d) Higher λmax in each pair10 marks Answered
- Q5(e) Number of ¹H NMR signals and order of chemical shift10 marks Answered
- Q7(a) λmax of three dienones by Woodward–Fieser rules15 marks Question only
- Q7(c)(i) Two isomeric esters C₁₀H₁₂O₂10 marks Question only
- Q7(c)(ii) Fragment ions m/z 58 and m/z 9210 marks Question only
- Q8(a) Assignment of four C=O stretching bands15 marks Answered
- Q8(b)(ii) Order of J(Ha–Hb)5 marks Answered
- Q8(c)(i) Two alkenes from 2-chloro-2,3-dimethylbutane10 marks Answered
- Q8(c)(ii) Fragmentation of diethyl ether5 marks Answered
- Q8(c)(iii) Bond length of HCl from its moment of inertia5 marks Answered
2023
- Q5(a) Number of ¹H NMR signals in (A) and (B)10 marks Answered
- Q5(b) C=C stretch of methylenecyclopropane and methylenecyclobutane10 marks Answered
- Q6(a)(i) Energy change of HCl + D₂ → DCl + HD10 marks Question only
- Q6(a)(ii) C=O bands of butyric acid, its ethyl ester and its anhydride5 marks Question only
- Q6(c)(i) Structure of C₁₆H₂₅NO from IR and ¹H NMR10 marks Question only
- Q6(c)(ii) Order of chemical shift of the lettered protons10 marks Question only
- Q8(a)(i) Doxepin: site of ionisation, m/z 58 ion and metastable ion10 marks Answered
- Q8(a)(ii) Ketone C₇H₁₂O with λmax = 249 nm5 marks Answered
- Q8(b)(i) Microwave activity; rotational constants of CO10 marks Answered
- Q8(b)(ii) Expected J(Ha–Hb) in three alkenes5 marks Answered
- Q8(c)(i) Keto and enol percentages of acetylacetone from integration10 marks Answered
- Q8(c)(ii) Two isomeric amides C₅H₁₁NO by mass spectrometry5 marks Answered
- Q8(c)(iii) Fundamental vibrations of CO₂ and their IR activity5 marks Answered
2022
- Q5(d) N–H stretching of amines in IR; alcohols in PMR10 marks Answered
- Q5(e) Matching three sets of IR and NMR data with five structures10 marks Answered
- Q7(c)(i) Compound A (M = 102) and its cleavage products B and C10 marks Question only
- Q7(c)(ii) Three isomeric carbonyl compounds C₅H₁₀O10 marks Question only
- Q8(a)(i) Carbonyl stretching frequency of two acetylcyclohexenes5 marks Answered
- Q8(a)(ii) Dehydration of 1,2-dimethylcyclohexanol; telling the alkenes apart by IR10 marks Answered
- Q8(b)(i) λmax of two polyenes by Woodward–Fieser rules10 marks Answered
- Q8(b)(ii) λmax of 1,3-butadiene and 1,3,5-hexatriene5 marks Answered
- Q8(c)(i) McLafferty rearrangement; fragmentation of butyl butyrate10 marks Answered
- Q8(c)(ii) C₂H₂BrCl with J = 16 Hz; two dienones from UV data10 marks Answered
2021
- Q5(a) Five ¹H NMR signals of pentane-2,4-dione10 marks Answered
- Q5(e) McLafferty rearrangement in pentan-2-one; base peak of pentan-3-one10 marks Answered
- Q6(a)(i) Product of acetone with dilute sodium hydroxide from its spectra15 marks Question only
- Q6(a)(ii) Higher carbonyl stretching frequency in two pairs5 marks Question only
- Q7(c) Structure of a phenol C₁₀H₁₄O from IR, mass and NMR data15 marks Question only
- Q8(b)(i) C₉H₁₈O with a single ¹H NMR line10 marks Answered
- Q8(b)(ii) Two UV bands of acetone5 marks Answered
- Q8(c)(i) ¹H NMR spectrum of methyl propenoate10 marks Answered
- Q8(c)(ii) Two carbonyl bands of chloroacetone5 marks Answered
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