Indian Forest Service (Mains)
Chemistry optional
- 2 papers
- 200 marks each
- 3 h per paper
Paper II covers organic chemistry and spectroscopy.
Principles of spectroscopy and applications in structure elucidation: every question, 2021 to 2025
58 parts worth 385 marks have been set on this unit in UPSC IFoS 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.
(a) Rotational spectra: diatomic molecules; isotopic substitution and rotational constants. (b) Vibrational spectra: diatomic molecules, linear triatomic molecules, specific frequencies of functional groups in polyatomic molecules. (c) Electronic spectra: singlet and triplet states. n→π* and π→π* transitions; application to conjugated double bonds and conjugated carbonyls, Woodward-Fieser rules. (d) Nuclear magnetic resonance: isochronous and anisochronous protons; chemical shift and coupling constants; application of ¹H NMR to simple organic molecules. (e) Mass spectra: parent peak, base peak, daughter peak, metastable peak, fragmentation of simple organic molecules; α-cleavage, McLafferty rearrangement. (f) Electron spin resonance: inorganic complexes and free radicals.
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
Notes: ESR (EPR) spectroscopy: g-value, hyperfine splitting, radical anions, metal ions and spin labels (full notes) · short notes
2025
- Q5(d) Proton NMR of dry ethanol5 marks Answered
- Q5(e) Mass fragmentation of acetic anhydride5 marks Answered
- Q5(f) Structure from combined spectra15 marks Answered
- Q6(b)(i) Two ester NMR patterns5 marks Question only
- Q6(b)(ii) A symmetric malonate ester5 marks Question only
- Q7(b)(i) Checking the conjugated chromophore5 marks Question only
- Q7(b)(ii) Conjugated and non-conjugated ketones5 marks Question only
- Q8(a)(i) CO rotational constant and bond length10 marks Answered
- Q8(a)(ii) Isotopic change in rotational constant5 marks Answered
- Q8(b)(i) Isotope exchange and zero-point energy10 marks Answered
- Q8(b)(ii) Hot-band population in iodine10 marks Answered
2024
- Q5(b) Zero-point vibrational energy5 marks Answered
- Q5(f) IR comparison of two secondary amides5 marks Answered
- Q5(g) Chlorine and bromine isotope patterns5 marks Answered
- Q5(h) Spin labels for macromolecules5 marks Answered
- Q7(b)(i) UV bands of a ketone and an enone10 marks Question only
- Q7(b)(ii) Woodward–Fieser estimates for two tetraenes5 marks Question only
- Q7(c) Identification of an amino ester15 marks Question only
- Q8(a)(i) Axial versus equatorial alpha chlorine5 marks Answered
- Q8(a)(ii) IR-active vibrations5 marks Answered
- Q8(b) Mass spectra of benzyl alcohol and anisole10 marks Answered
- Q8(c)(i) NMR distinction of two isomer pairs10 marks Answered
- Q8(c)(ii) Structure from an aldol-condensation spectrum10 marks Answered
2023
- Q5(d) Woodward–Fieser calculation and a name error5 marks Answered
- Q5(e) Distinguishing ortho and para xylene5 marks Answered
- Q5(f) Chemical and magnetic equivalence in styrene5 marks Answered
- Q5(g) Parent ion from a metastable peak5 marks Answered
- Q6(c) Two C3H6O carbonyl compounds5 marks Answered
- Q6(d) Meaning of a coupling constant5 marks Answered
- Q6(e) Intensity of alkene and ketone UV absorption5 marks Answered
- Q6(f) Isotopic substitution in rotational spectra5 marks Answered
- Q7(e) Two unsaturated ester isomers5 marks Answered
- Q7(g) Chemical-shift separation in Hz5 marks Answered
- Q7(h) Hydration of phenylacetylene5 marks Answered
- Q8(b) A C9H12 alkylbenzene mass spectrum5 marks Question only
- Q8(c) Benzene radical anion5 marks Question only
- Q8(e) Identification of glutaric anhydride15 marks Question only
2022
- Q5(d) CO bond length from rotational spacing5 marks Answered
- Q5(e) Isotope shift of C–H stretching5 marks Answered
- Q5(f) Relative carbonyl stretching frequencies5 marks Answered
- Q7(a) Woodward–Fieser calculations10 marks Answered
- Q7(b) Tautomers and chromophores5 marks Answered
- Q7(c) ESR of pyrazine5 marks Answered
- Q7(d) Infrared distinctions10 marks Answered
- Q8(a) N–H identification in hexamethylenediamine5 marks Answered
- Q8(b) Aromatic proton coupling constants5 marks Answered
- Q8(c) Matching mass-spectral behaviour10 marks Answered
- Q8(d) Diphenyl ether and its mass fragments10 marks Answered
- Q8(e) A fragrant aromatic aldehyde10 marks Answered
2021
- Q1(h) Hyperfine lines of an isotopic radical5 marks Answered
- Q3(a)(ii) Strongly shielded internal methyl groups5 marks Answered
- Q3(c)(i) ESR resonance field5 marks Answered
- Q5(e) Azobenzene and hydrazobenzene5 marks Answered
- Q8(a)(i) Methylcyclohexenes by mass spectrometry5 marks Question only
- Q8(a)(ii) Hydroxy-methoxyacetophenone assignment5 marks Question only
- Q8(b) Identification of an aromatic diester10 marks Question only
- Q8(c)(i) Oxidative coupling of acetic anhydride5 marks Question only
- Q8(e) IR distinctions between functional groups5 marks Question only