Tautomerism is shown by

Options

A. `CH_(3)-O-NO`
B. `CH_(3)-CH_(2)-NO_(2)`
C. `CH_(3)CH_(2)CN`
D. `CH_(3)-underset(CH_(3))underset(|)(CH)-CH`

Answer

To determine which compounds exhibit tautomerism, we need to understand the concept of tautomerism itself. Tautomerism is a type of isomerism where two or more isomers (tautomers) can readily interconvert, typically involving the relocation of a hydrogen atom and a shift of a double bond. The most common example of tautomerism is keto-enol tautomerism.

### Step-by-Step Solution:

1. **Identify the Functional Groups**:
- Look for compounds that contain functional groups capable of tautomerism. Common functional groups include carbonyl (C=O) and hydroxyl (–OH) groups.

2. **Check for Alpha Hydrogen**:
- Ensure that there is at least one alpha hydrogen (a hydrogen atom attached to the carbon adjacent to the carbonyl carbon). This is crucial for the tautomerization process.

3. **Draw the Tautomeric Forms**:
- For each compound, draw the two forms: the keto form (with the carbonyl group) and the enol form (with the hydroxyl group and a double bond).

4. **Analyze the Stability**:
- Determine which tautomer is more stable. Generally, the keto form is more stable than the enol form due to stronger C=O bonds compared to C=C bonds.

5. **Conclude on Tautomerism**:
- If both forms can interconvert and meet the criteria of having a pi bond adjacent to an electronegative atom and an alpha hydrogen, then the compound exhibits tautomerism.

### Example:
- Consider the compound acetone (CH3COCH3):
- **Keto Form**: CH3COCH3 (carbonyl group)
- **Enol Form**: CH3C(OH)=CH2 (hydroxyl group and double bond)
- Since it has an alpha hydrogen and can interconvert, it shows tautomerism.

### Final Conclusion:
- Based on the analysis, compounds with carbonyl groups and the presence of alpha hydrogens, such as ketones and aldehydes, exhibit tautomerism.