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: Iodoform Test Principles
A positive Iodoform test is observed with:
- Methyl ketones (\( R-CO-CH_3 \))
- Acetaldehyde (\( CH_3CHO \))
- Alcohols that can be oxidized to methyl ketones or acetaldehyde (e.g., ethanol, secondary alcohols like 2-propanol)

Step 2: Analysis of Options
- Ethanol (\( CH_3CH_2OH \)): This primary alcohol oxidizes to acetaldehyde (\( CH_3CHO \)), a compound that yields a positive Iodoform test.
- Propanol:
- 1-Propanol (\( CH_3CH_2CH_2OH \)) oxidizes to propanal (\( CH_3CH_2CHO \)), which does not meet the criteria for a positive test.
- 2-Propanol (\( CH_3CH(OH)CH_3 \)) oxidizes to acetone (\( CH_3COCH_3 \)), a methyl ketone, which yields a positive test. Assuming "propanol" refers to 1-propanol, the test is negative.
- Methanol (\( CH_3OH \)): This primary alcohol oxidizes to formaldehyde (\( HCHO \)), which results in a negative test.
- Methanal (\( HCHO \)): Formaldehyde does not possess the necessary structural features for a positive Iodoform test. Negative test.

Step 3: Determination
Ethanol is the only compound among the given options that consistently produces a positive Iodoform test.