The order of stability of the following tautomeric compound is
`underset("(I)")(CH_(2)=C(OH)-CH_(2)-CO-CH_(3))`
`underset("(II)")(rarrCH_(3)-CO-CH_(2)-CO-CH_(3))`
`underset("(III)")(rarrCH_(3)-C(OH)=CH-CO-CH_(3))`

Options

A. `III gt II gt I`
B. `II gt I gt III`
C. `II gt I gt III`
D. `I gt II gt III`

Answer

To determine the order of stability of the given tautomeric compounds, we will analyze each compound based on their structural features, particularly focusing on the presence of keto-enol forms, hydrogen bonding, and conjugation.

### Step 1: Identify and Write Down the Compounds
1. **Compound (I)**: \( CH_2=C(OH)-CH_2-CO-CH_3 \)
2. **Compound (II)**: \( CH_3-CO-CH_2-CO-CH_3 \)
3. **Compound (III)**: \( CH_3-C(OH)=CH-CO-CH_3 \)

### Step 2: Analyze Compound (I)
- Compound (I) is an enol form.
- It has a hydroxyl group (–OH) attached to a carbon that is part of a double bond.
- There is no significant conjugation present in this compound.
- The stability is relatively low due to the lack of resonance and hydrogen bonding.

### Step 3: Analyze Compound (II)
- Compound (II) is a keto form.
- Keto forms are generally more stable than enol forms due to the greater strength of the carbonyl (C=O) bond compared to the C=C bond in enols.
- This compound has no hydroxyl group, which means it lacks the potential for hydrogen bonding.

### Step 4: Analyze Compound (III)
- Compound (III) is also an enol form but has a hydroxyl group attached to a carbon that is part of a double bond.
- This compound can form hydrogen bonds due to the presence of the –OH group.
- Additionally, there is conjugation present in this compound, which enhances its stability.
- The presence of both hydrogen bonding and conjugation makes this compound the most stable among the three.

### Step 5: Determine the Order of Stability
Based on the analysis:
- **Most Stable**: Compound (III) due to hydrogen bonding and conjugation.
- **Moderately Stable**: Compound (II) as it is a keto form.
- **Least Stable**: Compound (I) due to lack of conjugation and lower stability of the enol form.

### Final Order of Stability
The order of stability is:
\[ \text{(III) > (II) > (I)} \]