Which of the following fails to answer the iodoform test

Options

A. Pentanone-1
B. Pentanone-2
C. Propanone-2
D. Ethanol

Explanation

To solve the problem of which compound fails to answer the iodoform test, we need to understand the criteria for the iodoform test and analyze the given options accordingly.

### Step-by-Step Solution:

1. **Understand the Iodoform Test**:
The iodoform test is a qualitative test used to identify the presence of a methyl ketone (RCOCH3) or a primary alcohol that can be oxidized to a methyl ketone. Compounds that contain the structure CH3CO- (methyl ketone) or CH3CH(OH)- (secondary alcohol) will give a positive result.

2. **Analyze Each Compound**:
- **Pent-2-one**: This is a ketone with the structure CH3COC3H7. It has a methyl group adjacent to the carbonyl group, so it will give a positive iodoform test.
- **Pent-1-one**: This is a ketone with the structure CH3(CH2)3COCH3. It does not have a methyl group adjacent to the carbonyl, so it will not give a positive iodoform test.
- **Propane-2-one (Acetone)**: This is a methyl ketone (CH3COCH3) and will give a positive iodoform test.
- **Ethanol**: This is a primary alcohol (CH3CH2OH) and can be oxidized to acetaldehyde (CH3CHO), which can then be converted to a methyl ketone. Thus, it will give a positive iodoform test.

3. **Identify the Compound that Fails the Test**:
From the analysis, we can see that Pent-1-one is the only compound that does not have the required structure to give a positive iodoform test.

### Conclusion:
The compound that fails to answer the iodoform test is **Pent-1-one**.