UPSC Combined Geo-Scientist, Mains · 2021 · Mains Paper III

Q8(d). 2-Butenes: anti addition of bromine, syn hydroxylation

8 marks
Topic: Addition reactions
Question only

Question

Out of cis-2-butene or trans-2-butene, which one will give racemic-2,3-dibromobutane or meso-butane-2,3-diol on treatment with Br₂/CCl₄ and KMnO₄, respectively? Justify your answer.

Model answer

The free solution for 2021 answers questions 1, 2, 5, 6, 7 and 10, the ones picked in its time plan. Question 8 is answered in full in the Geo-Scientist Chemistry Paper III, 2021 to 2025 book, with every part of every paper.

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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

Printed copy Kindle edition Read sample pages

Topic notes: addition to alkenes and alkynes (Markovnikov, stereochemistry, dienes), with every Civil Services, IFoS and Geo-Scientist PYQ →

Topic notes: stereochemistry and conformational analysis (R/S, E/Z, Fischer and Newman projections, cyclohexane chair), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversanti addition of brominebromonium ionsyn hydroxylationmeso and racemic2-butene stereochemistry

All parts of Question 8

8(a) Cyclohexanone: Wolff–Kishner reduction and Reformatsky reaction10 marks
8(b) Eucarvone and light: 4π electrocyclic ring closure8 marks
8(c) Cyclohexane-1,2-dione and NaOH: benzilic acid ring contraction4 marks
8(d) 2-Butenes: anti addition of bromine, syn hydroxylation8 marks