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Aldehydes, Ketones and Carboxylic Acids
Iodoform Test
1 question from 1 paper, each with its answer.
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Concepts tested
- Structural requirement for iodoform test
All Questions
2004 AIPMT 1 question
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Which of the following will not form a yellow precipitate on heating with an alkaline solution of iodine :-Heating with iodine and alkali gives a yellow precipitate of iodoform, $CHI_3$, only if the compound contains the $CH_3CO-$ group or the $CH_3CH(OH)-$ group (which is first oxidised to $CH_3CO-$).
$CH_3CH_2CH(OH)CH_3$ (butan-2-ol) has the $CH_3CH(OH)-$ group; it gives iodoform.
$CH_3CH_2OH$ (ethanol) has $CH_3CH(OH)-$ with H as the other group; it is oxidised to $CH_3CHO$ and gives iodoform.
$CH_3CH(OH)CH_3$ (propan-2-ol) has the $CH_3CH(OH)-$ group; it gives iodoform.
$CH_3OH$ (methanol) has only one carbon. It cannot give a $CH_3CO-$ group (it is oxidised to HCHO), so it does not give the iodoform test.
So methanol, $CH_3OH$, will not form a yellow precipitate.