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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 · 2023 · Paper II

Q5(e). Photolysis of acetone: vapour phase and room temperature

Question

Identify the products in the above reactions with plausible mechanism. [photolysis (hν) of acetone (i) in the vapour phase and (ii) at room temperature; schemes given in the paper]

Answer in brief

Both begin with Norrish type I α-cleavage to CH₃CO· + ·CH₃; hot vapour gives ethane and CO, while at room temperature the acetyl radical couples to biacetyl, with ethane and some methane.

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Topic notes: organic photochemistry and Norrish reactions, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversNorrish type Iacetone photolysisα-cleavageacetyl radicalbiacetyldecarbonylation

All parts of Question 5