The syllabus of UPSC Chemistry optional subject can be broadly categorized into two sections: Paper I and Paper II. Here is a detailed explanation of the syllabus:

Paper I:
1. Atomic structure and chemical bonding:
- Quantum theory, wave-particle duality, atomic structure, and the periodic table.
- Chemical bonding, ionic and covalent bonds, hybridization, and molecular orbital theory.
2. Solid-state chemistry:
- Crystal systems, Bragg's law, packing in solids, and lattice defects.
- Band theory of metals, semiconductors, and insulators.
3. Coordination compounds:
- Werner's theory, crystal field theory, and valence bond theory.
- Nomenclature, isomerism, and electronic spectra of coordination compounds.
4. Thermodynamics and chemical equilibrium:
- Laws of thermodynamics, entropy, and spontaneity.
- Chemical equilibrium, Le Chatelier's principle, and solubility products.
5. Electrochemistry:
- Electrochemical cells, Nernst equation, and conductance.
- Batteries, fuel cells, and corrosion.
6. Chemical kinetics:
- Rate of reaction, order, and molecularity.
- Factors affecting the rate of reaction, determination of rate constants, and enzyme kinetics.
7. Photochemistry:
- Absorption of light, laws of photochemistry, and photochemical reactions.
- Photophysical processes, photosensitization, and photochemical transformations.
8. Surface chemistry:
- Adsorption, catalysis, and colloids.
- Emulsions, micelles, and heterogeneous catalysis.

Paper II:
1. Quantum chemistry:
- Quantum mechanics, Schrödinger equation, and its applications.
- Molecular orbital theory, Huckel molecular orbital theory, and spectroscopy.
2. Spectroscopy:
- Rotational, vibrational, and electronic spectroscopy.
- Magnetic resonance spectroscopy and mass spectrometry.
3. Analytical chemistry:
- Principles and applications of various analytical techniques.
- Chromatography, spectroscopy, and electroanalytical techniques.
4. Organic chemistry:
- Structure, nomenclature, and reactions of organic compounds.
- Stereochemistry, reaction mechanisms, and polymers.
5. Inorganic chemistry:
- Principles and reactions of inorganic compounds.
- Transition elements, lanthanides, actinides, and their coordination compounds.
6. Bioinorganic chemistry:
- Metalloproteins, metalloenzymes, and their applications.
- Role of metals in biological systems.
7. Polymer chemistry:
- Classification, synthesis, and reactions of polymers.
- Polymerization processes and polymer properties.

It is important to note that the syllabus may be subject to periodic revisions. Candidates are advised to refer to the official UPSC website or relevant study materials for the most updated syllabus.