Which of the following exhibits tautomerism ?

Options

A. `(CH_(3))_(2) NH`
B. `(CH_(3))_(3)CNO`
C. `R_(3)CNO_(2)`
D. `RCH_(2)NO_(2)`

Answer

To determine which of the given compounds exhibits tautomerism, we need to analyze each compound for the presence of alpha hydrogen atoms and the ability to undergo tautomeric shifts. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
We have four compounds to analyze. Let's denote them as:
1. Compound A
2. Compound B
3. Compound C
4. Compound D

### Step 2: Draw the Structures
1. **Compound A**: CH3-NH-CH3
- Structure:
```
H
|
CH3-N-CH3
```

2. **Compound B**: CH3-N=O
- Structure:
```
O
||
CH3-N
```

3. **Compound C**: R-N=O (with an oxygen coordinated)
- Structure:
```
O
||
R-N
```

4. **Compound D**: R-CH-N=O (with an oxygen coordinated)
- Structure:
```
O
||
R-C-H
|
N
```

### Step 3: Check for Alpha Hydrogen
Tautomerism typically involves the transfer of a hydrogen atom from an alpha carbon to a nitrogen or oxygen atom.

- **Compound A**: No alpha hydrogen (the nitrogen is bonded to two methyl groups).
- **Compound B**: No alpha hydrogen (the nitrogen is bonded to one methyl group and has a double bond with oxygen).
- **Compound C**: No alpha hydrogen (the nitrogen is bonded to R and has a double bond with oxygen).
- **Compound D**: Has alpha hydrogen (the carbon adjacent to nitrogen has hydrogen atoms).

### Step 4: Identify Tautomerism
Only **Compound D** can undergo tautomerism because it has alpha hydrogen atoms. The tautomeric shift involves the transfer of a hydrogen atom from the alpha carbon to the nitrogen, resulting in a different structural form.

### Step 5: Conclusion
Only **Compound D** exhibits tautomerism.

### Final Answer
The compound that exhibits tautomerism is **Compound D**.

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