Question

Which of the following does NOT exhibit haloform reaction?

• A. Ethanal
• B. Propanal
• C. Propanone
• D. Butanone

Hint:

Ethanal (Acetaldehyde) is an incredibly important exception to memorize. It is the ONLY aldehyde in existence that gives a positive Iodoform test, because it's the only aldehyde with a $\text{CH}_3$ bonded directly to the $\text{C=O}$ group!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
We must identify which specific organic compound from the given list lacks the strict structural requirements necessary to undergo the haloform (iodoform) reaction.

Step 2: Detailed Explanation:
The haloform reaction is a classic qualitative test. A positive haloform reaction requires the molecule to possess a very specific structural feature:
A methyl ketone group ($\text{CH}_3\text{-C(=O)}-$).
(Alternatively, it can be a secondary alcohol that possesses a $\text{CH}_3\text{-CH(OH)}-$ group, because the oxidizing conditions of the test reagent will immediately oxidize it into a methyl ketone).
Let's evaluate the chemical structure of each option:
(c) Propanone (Acetone, $\text{CH}_3\text{-CO-CH}_3$): Contains two methyl ketone groups. It will give a strong positive test.
(d) Butanone (Ethyl methyl ketone, $\text{CH}_3\text{-CO-CH}_2\text{-CH}_3$): Contains one methyl ketone group on the left side. It will give a positive test.
(a) Ethanal (Acetaldehyde, $\text{CH}_3\text{-CHO}$): This is the ONLY aldehyde that gives a positive haloform test. By replacing the generic 'R' of a ketone with an 'H', you still possess the required $\text{CH}_3\text{-CO}-$ structure. It will give a positive test.
(b) Propanal (Propionaldehyde, $\text{CH}_3\text{-CH}_2\text{-CHO}$): The carbonyl carbon is attached to a hydrogen atom and an ethyl group. It completely lacks a terminal methyl group attached directly to the carbonyl carbon. Therefore, it absolutely cannot undergo the haloform reaction.

Step 3: Final Answer:
Propanal does NOT exhibit the haloform reaction, matching option (b).