Question

The compound that does not answer iodoform test is

• A. Ethanal
• B. Acetone
• C. Ethanoic acid
• D. Acetophenone

Hint:

To quickly check for a positive iodoform test, look for the CH\(_3\)CO- group or a CH\(_3\)CH(OH)- group. Remember that carboxylic acids, esters, and amides containing a CH\(_3\)CO- moiety do not give this test.

Answer 1

The Correct Option is C

Step 1: Understanding the Iodoform Test:
The iodoform test (reaction with I\(_2\) and NaOH) is a qualitative test for the presence of a methyl ketone group (CH\(_3\)-C(=O)-) or an alcohol group (CH\(_3\)-CH(OH)-) which can be oxidized to a methyl ketone under the test conditions. A positive test is indicated by the formation of a yellow precipitate of iodoform (CHI\(_3\)).
Step 2: Analyzing the given compounds:
(A) Ethanal (Acetaldehyde, CH\(_3\)CHO): The structure contains a CH\(_3\)-C(=O)- group attached to a hydrogen. It fulfills the condition for the iodoform test and gives a positive result.
(B) Acetone (Propanone, CH\(_3\)COCH\(_3\)): The structure contains a CH\(_3\)-C(=O)- group. It is a methyl ketone and gives a positive iodoform test.
(C) Ethanoic acid (Acetic acid, CH\(_3\)COOH): The structure contains a CH\(_3\)-C(=O)- group, but it is part of a carboxylic acid functional group. The acidic proton of the -COOH group reacts with the NaOH base preferentially. This prevents the abstraction of the \(\alpha\)-hydrogen, which is the first step of the haloform reaction mechanism. Therefore, carboxylic acids do not give a positive iodoform test.
(D) Acetophenone (C\(_6\)H\(_5\)COCH\(_3\)): The structure contains a CH\(_3\)-C(=O)- group attached to a phenyl ring. It is a methyl ketone and gives a positive iodoform test.
Step 3: Conclusion:
Among the given options, only ethanoic acid does not have the required structure or reactivity to undergo the iodoform reaction.
Step 4: Final Answer:
The compound that does not answer the iodoform test is ethanoic acid.