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Chemistry Question on Aldehydes, Ketones and Carboxylic Acids

Which of the following compounds will give a yellow precipitate with iodine and alkali ?

A

Methyl acetate

B

Acetamide

C

2-Hydroxypropane

D

Acetophenone

Answer

2-Hydroxypropane

Explanation

Solution

Out of the given compounds, only CH3−CH∣ OH −CH3C{{H}_{3}}-\underset{OH}{\mathop{\underset{|}{\mathop{CH}}\,}}\,-C{{H}_{3}}
(2-hydroxyprepane)gives yellow precipitate with iodine and alkali (iodoform test).But CH3−COO−CH3C{{H}_{3}}-COO-C{{H}_{3}}
(methyl acetate), CH3−CO−NH2C{{H}_{3}}-CO-N{{H}_{2}}
(accetamide), do not perform this test because α−H\alpha -H
is not active due to +M effect of nearby group. CH3−CH∣ OH −CH3+4I2+6NaOHC{{H}_{3}}-\underset{OH}{\mathop{\underset{|}{\mathop{CH}}\,}}\,-C{{H}_{3}}+4{{I}_{2}}+6NaOH
→CHI3Iodoform (yellowppt) ↓+CH3COONa+5NaI+5H2O\xrightarrow{{}}\underset{\begin{smallmatrix} Iodoform \\\ (yellow\,ppt) \end{smallmatrix}}{\mathop{CH{{I}_{3}}}}\,\downarrow +C{{H}_{3}}COONa+5NaI+5{{H}_{2}}O