Which of the following is most stable ?

Options

A.
B.
C.
D.

Explanation

To determine which of the given systems is the most stable, we need to analyze the electronic structure and aromaticity of each system. Here’s a step-by-step solution:

### Step 1: Identify the Electron Count
- For the first system, we have **2 π electrons**.
- For the second system, we have **4 π electrons**.

### Step 2: Determine Hybridization and Planarity
- Check the hybridization of the atoms involved:
- In the first system, all atoms are **sp² hybridized**, which indicates a planar structure.
- In the second system, we also check for planarity, and it is cyclic.

### Step 3: Apply Hückel's Rule
- According to Hückel's rule, a cyclic, planar molecule is aromatic if it has **(4n + 2) π electrons**, where n is a non-negative integer.
- For the first system with **2 π electrons**:
- This fits the formula (4(0) + 2), making it **aromatic**.
- For the second system with **4 π electrons**:
- This does not fit the formula (4(1) + 2), making it **non-aromatic**.

### Step 4: Compare Stability
- Aromatic compounds are generally more stable due to resonance and delocalization of electrons.
- Non-aromatic compounds are less stable than aromatic ones.
- Therefore, the first system (aromatic with 2 π electrons) is more stable than the second system (non-aromatic with 4 π electrons).

### Conclusion
- The most stable system is the one with **2 π electrons**, which is aromatic.

### Final Answer
- The first system is the most stable.

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