Step 1: Understand the Iodoform test
Compounds that give a positive Iodoform test include:
- Methyl ketones ( )
- Acetaldehyde ( )
- Alcohols that oxidize to methyl ketones or acetaldehyde (e.g., ethanol, secondary alcohols like 2-propanol)
Step 2: Analyze each option
- Ethanol ( ): A primary alcohol. Under Iodoform test conditions (with iodine and a base), ethanol oxidizes to acetaldehyde ( ), which has the structure . Acetaldehyde reacts further to give iodoform. Thus, ethanol gives a positive test.
- Propanol: This could refer to 1-propanol ( ) or 2-propanol ( ).
- 1-Propanol oxidizes to propanal ( ), which lacks the methyl ketone structure, so it gives a negative test.
- 2-Propanol, a secondary alcohol, oxidizes to acetone ( ), 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 ( ): A primary alcohol that oxidizes to formaldehyde ( ), which lacks the required structure. Negative test.
- Methanal ( ): 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.