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 Concept:
The haloform reaction is given by compounds containing a methyl keto group ($-CO-CH_3$) or alcohols that can be oxidized to a methyl keto group (e.g., $CH_3-CH(OH)-R$).

Step 2: Formula Application:
Check the structure for the $CH_3-CO-$ group: - (a) Ethanal: $CH_3-CHO$ (Contains methyl keto equivalent). - (c) Propanone: $CH_3-CO-CH_3$ (Contains methyl keto). - (d) Butanone: $CH_3-CO-CH_2CH_3$ (Contains methyl keto).

Step 3: Explanation:
Propanal ($CH_3-CH_2-CHO$) is an aldehyde, but it lacks the specific methyl group directly attached to the carbonyl carbon ($CH_3-CO-$). Instead, it has an ethyl group attached to the formyl group. Therefore, it cannot form a haloform (like iodoform).

Step 4: Final Answer:
Propanal does not exhibit the haloform reaction.