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NEET CHEMISTRYEasy

The compound that will not form a yellow precipitate on heating with an alkaline solution of iodine is:

A

CH₃CH₂CH(OH)CH₃

B

CH₃OH

C

CH₃CH₂OH

D

CH₃CH(OH)CH₃

Step-by-Step Solution

The reaction described is the Iodoform test. A positive test (formation of a yellow precipitate of CHI3CHI_3) is given by compounds containing either a methyl ketone group (CH3−C=OCH_3-C=O) or a methyl carbinol group (CH3−CH(OH)−CH_3-CH(OH)-) attached to at least one hydrogen atom or alkyl/aryl group.

  1. Ethanol (CH3CH2OHCH_3CH_2OH): Contains the CH3−CH(OH)−CH_3-CH(OH)- group. (Positive test).
  2. Propan-2-ol (CH3CH(OH)CH3CH_3CH(OH)CH_3): Contains the CH3−CH(OH)−CH_3-CH(OH)- group. (Positive test).
  3. Butan-2-ol (CH3CH2CH(OH)CH3CH_3CH_2CH(OH)CH_3): Contains the CH3−CH(OH)−CH_3-CH(OH)- group. (Positive test).
  4. Methanol (CH3OHCH_3OH): Does not contain the requisite CH3−CH(OH)−CH_3-CH(OH)- group. Therefore, it does not give a yellow precipitate with alkaline iodine.
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