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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

Q8(a)(ii). Dehydration of 1,2-dimethylcyclohexanol; telling the alkenes apart by IR

Question

Complete the following reaction. Write the structures of A, B and C, and explain how IR spectroscopy is helpful to distinguish among them: 1,2-dimethylcyclohexanol with H⁺ gives A + B + C. [structure given in the paper]

Answer in brief

A = 1,2-dimethylcyclohexene (major); B = 1,6-dimethylcyclohexene; C = 1-methyl-2-methylidenecyclohexane (least). They differ in the =C–H and C=C bands.

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Topic notes: IR spectroscopy: group frequencies, carbonyl stretching and hydrogen bonding, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversE1 dehydrationSaytzeff ruleIR of alkenes=C–H out-of-plane bendingexocyclic methylene

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