Stability order among these tautomer is :
`CH_(2)=overset(OH)overset(|)underset((I))C-CH_(2)-CH_(3)hArrCH_(3)-overset(O)overset(||)underset((II))(C)-CH_(2)-CH_(3)hArrCH_(3)-overset(OH)overset(|)(C)=underset((III))(CH)-CH_(3)`

Options

A. `IgtIIgtIII`
B. `IIIgtIIgtI`
C. `IIgtIgtIII`
D. `IIgtIIIgtI`

Answer

To determine the stability order among the given tautomers, we will analyze the structures and their respective stability based on the presence of alpha hydrogens and the keto-enol tautomerism concept.

### Step-by-Step Solution:

1. **Identify the Structures**:
- **Structure I**: CH₂=CHO-CH₂-CH₃
- **Structure II**: CH₃-C(=O)-CH₂-CH₃
- **Structure III**: CH₃-CH=CH-CHO

2. **Analyze Structure II (Keto Form)**:
- Structure II is a keto form (C=O), which is generally more stable than the enol form due to the presence of a strong carbonyl bond.
- This structure has no alpha hydrogens, making it very stable.

3. **Analyze Structure I (Enol Form)**:
- Structure I is an enol form (C=C-OH).
- It has 2 alpha hydrogens (from the CH₂ groups adjacent to the carbonyl).
- Enols are typically less stable than their keto counterparts, but the presence of alpha hydrogens can enhance stability.

4. **Analyze Structure III (Enol Form)**:
- Structure III is also an enol form (C=C-CHO).
- It has only 1 alpha hydrogen (from the CH group adjacent to the carbonyl).
- Fewer alpha hydrogens generally lead to lower stability compared to structures with more alpha hydrogens.

5. **Comparing Structures**:
- Between Structure I and Structure III, Structure I is more stable because it has more alpha hydrogens (2 vs. 1).
- Structure II is the most stable due to being a keto form.
- Therefore, the stability order is:
- **Most Stable**: Structure II
- **Second Stable**: Structure I
- **Least Stable**: Structure III

6. **Final Stability Order**:
- The final stability order among the tautomers is:
- II > I > III