Which of the following ketonic compound is the least stable?

Options

A.
B.
C.
D.

Explanation

To determine which ketonic compound is the least stable, we can analyze the stability of the keto and enol forms of the given compounds. Here’s a step-by-step solution:

### Step 1: Understand Ketones and Tautomerization
Ketones can exist in two forms: the keto form and the enol form. Tautomerization is the process where a keto form can convert to an enol form, especially if there are alpha hydrogens present.

**Hint:** Remember that the presence of alpha hydrogens allows for tautomerization between keto and enol forms.

### Step 2: Analyze Compound D
In the case of compound D, which is a cyclic triketone, we need to check for the presence of alpha hydrogens. Each ketone group in compound D has alpha hydrogens, allowing for tautomerization.

**Hint:** Look for alpha hydrogens in the structure of the ketonic compounds to determine if tautomerization can occur.

### Step 3: Tautomerization in Compound D
When tautomerization occurs in compound D, the alpha hydrogens can transfer, leading to the formation of an enol that has three double bonds and OH groups. This enol form gains aromaticity, which significantly increases its stability.

**Hint:** Aromatic compounds are generally more stable due to resonance and conjugation. Identify if the enol form can achieve aromaticity.

### Step 4: Compare Stability of Other Compounds
For the other ketonic compounds, when we analyze their enol forms, we find that they do not gain aromaticity. Therefore, their keto forms remain non-aromatic and are less stable compared to the aromatic enol form of compound D.

**Hint:** If the enol form does not achieve aromaticity, the keto form will be relatively more stable.

### Step 5: Conclusion
Since compound D can achieve aromaticity in its enol form, it is less stable in its keto form compared to the other ketonic compounds, which do not gain such stability. Therefore, the least stable ketonic compound is option D.

**Final Answer:** The least stable ketonic compound is **option D**.