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 compound exhibits tautomerism, we need to analyze each option provided in the question. Tautomerism is a type of isomerism where two or more compounds (tautomers) can readily interconvert, typically involving the transfer of a hydrogen atom and a shift in the position of a double bond.

### Step-by-Step Solution:

1. **Analyze Option A: CH3ONO**
- **Structure**: The structure can be drawn as CH3-N=O.
- **Alpha Hydrogens**: Check for alpha hydrogens. The nitrogen atom does not have any alpha hydrogen atoms attached to it.
- **Conclusion**: Since there are no alpha hydrogens, this compound does not exhibit tautomerism.

2. **Analyze Option B: CH3CH2C=O**
- **Structure**: The structure can be drawn as CH3-CH2-C(=O).
- **Alpha Hydrogens**: There are two alpha hydrogens on the CH2 group adjacent to the carbonyl (C=O).
- **Tautomerism Condition**: The double bond can shift, and the alpha hydrogen can be removed to form a resonance structure.
- **Conclusion**: This compound shows tautomerism, as it can interconvert between its keto and enol forms.

3. **Analyze Option C: CH3CH2CN**
- **Structure**: The structure can be drawn as CH3-CH2-C≡N.
- **Alpha Hydrogens**: There are alpha hydrogens present on the CH2 group.
- **Tautomerism Condition**: However, the presence of a triple bond (C≡N) does not allow for the necessary resonance or hydrogen transfer that characterizes tautomerism.
- **Conclusion**: This compound does not exhibit tautomerism.

4. **Analyze Option D: CH3CH2C**
- **Structure**: The structure is incomplete as it lacks a double bond or functional group.
- **Alpha Hydrogens**: There are alpha hydrogens present, but without a double bond or functional group, tautomerism cannot occur.
- **Conclusion**: This compound does not show tautomerism.

### Final Answer:
The compound that shows tautomerism is **Option B: CH3CH2C=O**.