Question

Which of the following compounds will give a positive Iodoform test?

• A. Ethanol
• B. Propanol
• C. Methanol
• D. Methanal

Hint:

Ethanol is the only primary alcohol that gives the iodoform test because it oxidizes to acetaldehyde.

Answer 1

The Correct Option is A

Step 1: Understand the Iodoform test
Compounds that give a positive Iodoform test include:
- Methyl ketones (\( R-CO-CH_3 \))
- Acetaldehyde (\( CH_3CHO \))
- Alcohols that oxidize to methyl ketones or acetaldehyde (e.g., ethanol, secondary alcohols like 2-propanol)

Step 2: Analyze each option
- Ethanol (\( CH_3CH_2OH \)): A primary alcohol. Under Iodoform test conditions (with iodine and a base), ethanol oxidizes to acetaldehyde (\( CH_3CHO \)), which has the structure \( CH_3-C(=O)-H \). Acetaldehyde reacts further to give iodoform. Thus, ethanol gives a positive test.
- Propanol: This could refer to 1-propanol (\( CH_3CH_2CH_2OH \)) or 2-propanol (\( CH_3CH(OH)CH_3 \)).
- 1-Propanol oxidizes to propanal (\( CH_3CH_2CHO \)), which lacks the methyl ketone structure, so it gives a negative test.
- 2-Propanol, a secondary alcohol, oxidizes to acetone (\( CH_3COCH_3 \)), a methyl ketone, which gives a positive test. However, since the question doesn’t specify and “propanol” typically implies 1-propanol in such contexts, we assume it’s 1-propanol, which gives a negative test.
- Methanol (\( CH_3OH \)): A primary alcohol that oxidizes to formaldehyde (\( HCHO \)), which lacks the required structure. Negative test.
- Methanal (\( HCHO \)): Formaldehyde does not have the methyl ketone or acetaldehyde structure. Negative test.

Step 3: Conclusion
Only ethanol consistently gives a positive Iodoform test among the options.