UPSC Combined Geo-Scientist
Chemist
- 3 descriptive papers
- 200 marks each
- 3 h per paper
Mains Paper III covers analytical and organic chemistry.
Addition reactions: every question, 2016 to 2025
23 parts worth 129 marks have been set on this unit in UPSC Geo-Scientist Chemistry Mains Paper III from 2016 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
Addition to C-C multiple bonds: mechanism of addition involving electrophiles, nucleophiles and free radicals (polymerization reactions of alkenes and substituted alkenes), Ziegler-Natta catalyst for polymerization, polyurethane, and conducting polymers; addition to conjugated systems (Diels-Alder reaction), orientation and reactivity (on simple cis- and trans- alkenes). Addition to carbon-heteroatom multiple bonds: addition to C=O double bond, structure and reactivity, hydration, addition of ROH, RSH, CN⁻, bisulphite, amine derivatives, hydride ions.
Notes: Addition to C=C and C≡C: Markovnikov, stereochemistry, dienes (full notes) · short notes
Notes: Stereochemistry and conformational analysis: R/S, E/Z, Fischer and Newman projections, cyclohexane (full notes) · short notes
2025
- Q6(b) Bromine addition: styrene reacts faster than propene4 marks Answered
- Q6(c) Addition of HCl to an α,β-unsaturated acid4 marks Answered
- Q6(e) Hydroboration–oxidation of 1-methylcyclohexene4 marks Answered
- Q9(a)(ii) Polyurethane: characteristic use and repeating unit5 marks Answered
- Q9(b)(i) HBr and buta-1,3-diene: kinetic and thermodynamic control5 marks Answered
2024
- Q6(b) HBr and a conjugated diene: 1,2- and 1,4-addition4 marks Answered
- Q6(e) Intramolecular oxymercuration–demercuration: a cyclic ether4 marks Answered
- Q7(d)(i) Iodolactonisation of a cyclopentenylacetic acid5 marks Answered
- Q8(a)(ii) Hydroboration–oxidation of norbornene: exo-norborneol5 marks Question only
2023
- Q6(c) Reductive amination, then intramolecular aza-Michael addition4 marks Answered
- Q6(e) Amidomercuration–demercuration of hex-1-ene in acetonitrile4 marks Answered
- Q8(c) Radical polymerisation of ethene; how branches form5 marks Question only
- Q9(b) Trialkylborane to aldehyde, ketone, alcohol and tertiary alcohol10 marks Question only
2022
- Q6(d) HCl with 1-methyl-1-vinylcyclobutane: ring expansion4 marks Answered
- Q7(a) Acetylene on a Ziegler–Natta catalyst: polyacetylene10 marks Answered
2021
- Q6(a) Reactivity of four alkenes towards electrophilic addition4 marks Answered
- Q6(e) Epoxidation of cholesterol with a peroxy acid4 marks Answered
- Q8(d) 2-Butenes: anti addition of bromine, syn hydroxylation8 marks Question only
- Q9(b) 1-Methylcyclopentene to 1- and 2-methylcyclopentanol8 marks Question only
2020
- Q6(b) Anionic polymerisation of substituted styrenes4 marks Answered
2019
- Q6(d) Peroxide effect4 marks Answered
2017
- Q8(a) Products and stereochemistry of two reactions10 marks Question only
- Q8(b) E2 elimination and deuteration: product stereochemistry10 marks Question only
UPSC Combined Geo-Scientist (Main) Chemistry Paper III: Model Answers 2021 to 2025
- All ten questions of each paper, with the question printed above its answer
- Instruments drawn as labelled diagrams, numericals worked with units
- Topic-wise weightage and a topic-wise index