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Tuesday, 6 October 2026 · New Delhi

UPSC CSE Mains · Optional Subject

Chemistry

The molecular world — atomic structure, bonding, reactions and spectroscopy.

Paper I

250marks

3 hours each

Paper II

250marks

3 hours each

Optional total

500marks

Counts toward the Mains merit

Paper I syllabus

250 marks · 3 hours

1. Atomic Structure :

  1. Heisenberg's uncertainty principle Schrodinger wave equation (time independent); Interpretation of wave function, particle in one-dimensional box, quantum numbers, hydrogen atom wave functions; Shapes of s, p and d orbitals.

2. Chemical bonding :

  1. Ionic bond, characteristics of ionic compounds, lattice energy, Born-Haber cycle; covalent bond and its general characteristics, polarities of bonds in molecules and their dipole moments; Valence bond theory, concept of resonance and resonance energy; Molecular orbital theory (LCAO method); bonding H2 +, H2 He2 + to Ne2, NO, CO, HF, CN–, Comparison of valence bond and molecular orbital theories, bond order, bond strength and bond length.

3. Solid state :

  1. Crystal systems; Designation of crystal faces, lattice structures and unit cell; Bragg's law; X-ray diffraction by crystals; Close packing, radius ratio rules, calculation of some limiting radius ratio values; Structures of NaCl, ZnS, CsCl, CaF2; stoichiometric and nonstoichiometric defects, impurity defects, semi-
  2. conductors.

4. The gaseous state and Transport Phenomenon :

  1. Equation of state for real gases, intermolecular interactions, and critical phenomena and liquefaction of gases; Maxwell’s distribution of speeds, intermolecular collisions, collisions on the wall and effusion; Thermal conductivity and viscosity of ideal gases.

5. Liquid State :

  1. Kelvin equation; Surface tension and surface energy, wetting and contact angle, interfacial tension and capillary action.

6. Thermodynamics :

  1. Work, heat and internal energy; first law of thermodynamics.
  2. Second law of thermodynamics; entropy as a state function, entropy changes in various processes, entropy-reversibility and irreversibility, Free energy functions; Thermodynamic equation of state; Maxwell relations; Temperature, volume and pressure dependence of U, H, A, G, Cp and Cv, and ; J-T effect and inversion temperature; criteria for equilibrium, relation between equilibrium constant and thermodynamic quantities; Nernst heat theorem, introductory idea of third law of thermodynamics.

7. Phase equilibria and solutions :

  1. Clausius-Clapeyron equation; phase diagram for a pure substance; phase equilibria in binary systems, partially miscible liquids—upper and lower critical solution temperatures; partial molar quantities, their significance and determination; excess thermodynamic functions and their determination.

8. Electrochemistry :

  1. Debye-Huckel theory of strong electrolytes and Debye-Huckel limiting Law for various equilibrium and transport properties.
  2. Galvanic cells, concentration cells; electrochemical series, measurement of e.m.f. of cells and its applications fuel cells and batteries.
  3. Processes at electrodes; double layer at the interface; rate of charge transfer, current density; overpotential; electroanalytical techniques : amperometry, ion selective electrodes and their use.

9. Chemical kinetics:

  1. Differential and integral rate equations for zeroth, first, second and fractional order reactions; Rate equations involving reverse, parallel, consecutive and chain reactions; Branching chain and explosions; effect of temperature and pressure on rate constant. Study of fast reactions by stop-flow and relaxation methods. Collisions and transition state theories.

10. Photochemistry:

  1. Absorption of light; decay of excited state by different routes; photochemical reactions between hydrogen and halogens and their quantum yields.

11. Surface phenomena and catalysis:

  1. Adsorption from gases and solutions on solid adsorbents; Langmuir and B.E.T. adsorption isotherms; determination of surface area, characteristics and mechanism of reaction on heterogeneous catalysts.

12. Bio-inorganic chemistry:

  1. Metal ions in biological systems and their role in ion-transport across the membranes (molecular mechanism), oxygen-uptake proteins, cytochromes and ferrodoxins.

13. Coordination chemistry :

  1. (i) Bonding in transition of metal complexes. Valence bond theory, crystal field theory and its modifications; applications of theories in the explanation of magnetism and electronic spectra of metal complexes.
  2. (ii) Isomerism in coordination compounds; IUPAC nomenclature of coordination compounds; stereochemistry of complexes with 4 and 6 coordination numbers; chelate effect and polynuclear complexes; trans effect and its theories; kinetics of substitution reactions in square-planar complexes; thermodynamic and kinetic stability of complexes.
  3. (iii) EAN rule, Synthesis structure and reactivity of metal carbonyls; carboxylate anions, carbonyl hydrides and metal nitrosyl compounds.
  4. (iv) Complexes with aromatic systems, synthesis, structure and bonding in metal olefin complexes, alkyne complexes and cyclopentadienyl complexes; coordinative unsaturation, oxidative addition reactions, insertion reactions, fluxional molecules and their characterization; Compounds with metal—metal bonds and metal atom clusters.

14. Main Group Chemistry:

  1. Boranes, borazines, phosphazenes and cyclic phosphazene, silicates and silicones, Interhalogen compounds; Sulphur—nitrogen compounds, noble gas compounds.

15. General Chemistry of ‘f’ Block Element:

  1. Lanthanides and actinides: separation, oxidation states, magnetic and spectral properties; lanthanide contraction.

Paper II syllabus

250 marks · 3 hours

1. Delocalised covalent bonding :

  1. Aromaticity, anti-aromaticity; annulenes, azulenes, tropolones, fulvenes, sydnones.

2. (i) Reaction mechanisms : General methods (both kinetic and non-kinetic) of study of

  1. mechanisms or organic reactions : isotopies, method cross-over experiment, intermediate trapping, stereochemistry; energy of activation; thermodynamic control and kinetic control of reactions.
  2. (ii) Reactive intermediates : Generation, geometry, stability and reactions of carboniumions and carbanions, free radicals, carbenes, benzynes and nitrenes. (iii) Substitution reactions :—SN 1, SN 2, and SN i, mechanisms ; neighbouring group participation; electrophilic and nucleophilic reactions of aromatic compounds including heterocyclic compounds—pyrrole, furan, thiophene and indole.
  3. (iv) Elimination reactions :—E1, E2 and E1cb mechanisms; orientation in E2 reactions— Saytzeff and Hoffmann; pyrolytic syn elimination—acetate pyrolysis, Chugaev and Cope eliminations.
  4. (v) Addition reactions :—Electrophilic addition to C=C and CC; nucleophilic addition to C=O, CN, conjugated olefins and carbonyls.
  5. (vi) Reactions and Rearrangements :—(a) Pinacol-pinacolone, Hoffmann, Beckmann, Baeyer- Villiger, Favorskii, Fries, Claisen, Cope, Stevens and Wagner—Meerwein rearrangements.
  6. (b) Aldol condensation, Claisen condensation, Dieckmann, Perkin, Knoevenagel, Witting, Clemmensen, Wolff-Kishner, Cannizzaro and von Richter reactions; Stobbe, benzoin and acyloin condensations; Fischer indole synthesis, Skraup synthesis, Bischler-Napieralski, Sandmeyer, Reimer-Tiemann and Reformatsky reactions.

3. Pericyclic reactions :—Classification and examples; Woodward-Hoffmann rules—electrocyclic

  1. reactions, cycloaddition reactions [2+2 and 4+2] and sigmatropic shifts [1, 3; 3, 3 and 1, 5], FMO approach.

4. (i) Preparation and Properties of Polymers: Organic polymerspolyethylene, polystyrene,

  1. polyvinyl chloride, teflon, nylon, terylene, synthetic and natural rubber.
  2. (ii) Biopolymers: Structure of proteins, DNA and RNA.

5. Synthetic Uses of Reagents:

  1. OsO4, HlO4, CrO3, Pb(OAc)4, SeO2, NBS, B2H6, Na-Liquid NH3, LiAIH4, NaBH4, n-BuLi, MCPBA.

6. Photochemistry :—Photochemical reactions of simple organic compounds, excited and ground

  1. states, singlet and triplet states, Norrish-Type I and Type II reactions.

7. Spectroscopy:

    Principle and applications in structure elucidation

    1. (i) Rotational—Diatomic molecules; isotopic substitution and rotational constants.
    2. (ii) Vibrational—Diatomic molecules, linear triatomic molecules, specific frequencies of functional groups in polyatomic molecules.
    3. (iii) Electronic—Singlet and triplet states.n and transitions; application to conjugated double bonds and conjugated carbonyls Woodward-Fieser rules; Charge transfer spectra.
    4. (iv) Nuclear Magnetic Resonance (1HNMR): Basic principle; chemical shift and spin-spin interaction and coupling constants.
    5. (v) Mass Spectrometry :—Parent peak, base peak, metastable peak, McLafferty rearrangement.

    Syllabus as per the official UPSC Civil Services (Main) Examination notification. Topic-wise study notes for Chemistry are being added — check back soon.

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