Which of the following compounds shows tautomerism

Options

A. HCHO
B. `CH_(3)CHO`
C. `CH_(3)COCH_(3)`
D. HCOOH

Explanation

To determine which of the given compounds shows tautomerism, we need to evaluate each option based on the necessary conditions for tautomerism. Tautomerism typically involves the presence of a functional group that can undergo a shift of a hydrogen atom and a rearrangement of bonds, often between a keto form and an enol form. The key requirements for tautomerism are:

1. The presence of a functional group that can undergo tautomerization (typically a carbonyl group).
2. The presence of an alpha hydrogen atom (H) on the carbon adjacent to the carbonyl carbon.

Now, let's analyze each compound:

### Step 1: Analyze Formaldehyde (HCHO)
- **Structure**: HCHO has no alpha carbon because it is an aldehyde with only one carbon atom.
- **Conclusion**: Since there is no alpha hydrogen, formaldehyde does not show tautomerism.

### Step 2: Analyze Acetaldehyde (CH3CHO)
- **Structure**: Acetaldehyde has the structure CH3CHO. The carbonyl carbon (C=O) is adjacent to the methyl group (CH3).
- **Alpha Hydrogen**: The methyl group has three alpha hydrogens.
- **Conclusion**: Acetaldehyde can undergo tautomerism, as it meets both conditions.

### Step 3: Analyze Acetone (CH3COCH3)
- **Structure**: Acetone has the structure CH3COCH3. The carbonyl carbon is flanked by two methyl groups.
- **Alpha Hydrogen**: Each methyl group has three alpha hydrogens.
- **Conclusion**: Acetone can also undergo tautomerism, satisfying the necessary conditions.

### Step 4: Analyze Formic Acid (HCOOH)
- **Structure**: Formic acid has the structure HCOOH. Similar to formaldehyde, it has no alpha carbon.
- **Conclusion**: Since there is no alpha hydrogen, formic acid does not show tautomerism.

### Final Conclusion
The compounds that show tautomerism from the given options are:
- Acetaldehyde (CH3CHO)
- Acetone (CH3COCH3)

### Summary of Results:
- **Formaldehyde**: Does not show tautomerism.
- **Acetaldehyde**: Shows tautomerism.
- **Acetone**: Shows tautomerism.
- **Formic Acid**: Does not show tautomerism.