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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper II covers organic chemistry and spectroscopy.

UPSC Civil Services (Mains), Chemistry optional · 2022 · Paper II

Q4(b)(i). Dibromocyclopentanes from cyclopentane and excess bromine

Question

If more than one equivalent of Br₂ at high temperature are allowed to react with cyclopentane, how many dibromocyclopentanes would you expect as products? Draw their structures and name them.

Answer in brief

Seven dibromocyclopentanes: three constitutional isomers (1,1-, 1,2- and 1,3-), counted with their stereoisomers; two of them are meso and two are racemic pairs.

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Topic notes: reactive intermediates (carbocations, carbanions, radicals, carbenes, nitrenes, benzyne), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversdibromocyclopentanefree radical brominationstereoisomersmeso compoundracemic mixture

All parts of Question 4