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JEE Advanced levelSingle correct optionDifficulty 3 of 3ap158

Three isomeric alcohols A, B and C of formula CHO are tested. A gives turbidity immediately with Lucas reagent. B gives turbidity after about 5 minutes and also gives a yellow precipitate with . C gives no turbidity at room temperature and on oxidation with PCC gives butanal. A, B and C are, respectively,

  1. A2-methylpropan-2-ol, butan-1-ol, butan-2-ol
  2. B2-methylpropan-2-ol, butan-2-ol, butan-1-ol
  3. Cbutan-1-ol, butan-2-ol, 2-methylpropan-2-ol
  4. Dbutan-2-ol, 2-methylpropan-2-ol, butan-1-ol

Answer: B

Immediate Lucas turbidity points to a tertiary alcohol (A = 2-methylpropan-2-ol). Turbidity in five minutes and the iodoform reaction mean a secondary alcohol with the unit, B = butan-2-ol. A primary alcohol that gives butanal on PCC oxidation must be the straight chain butan-1-ol.
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