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JEE Main 2018 · Chemistry · Alcohols, Phenols, Ethers and Haloalkanes · medium

Among the eight constitutional isomeric alcohols of molecular formula C5H12O, the number that on oxidation with PCC give a carbonyl compound which…

Single correct option

Among the eight constitutional isomeric alcohols of molecular formula C5H12O\mathrm{C_5H_{12}O}, the number that on oxidation with PCC give a carbonyl compound which responds to the iodoform test is
  1. A. 11
  2. B. 22
  3. C. 33
  4. D. 44
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Answer: (B) 22

Iodoform needs the CH3CO−\mathrm{CH_3CO-} group, so the alcohol must contain CH3CH(OH)−\mathrm{CH_3CH(OH)-}, which PCC oxidises to CH3CO−\mathrm{CH_3CO-}. Among C5H12O\mathrm{C_5H_{12}O} alcohols the candidates are pentan-2-ol (gives pentan-2-one) and 3-methylbutan-2-ol (gives 3-methylbutan-2-one). Pentan-3-ol gives a ketone without CH3CO\mathrm{CH_3CO}; primary alcohols give aldehydes (no CH3CO\mathrm{CH_3CO} unless ethanol); the tertiary alcohol 2-methylbutan-2-ol is not oxidised. Hence 22.
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