Which of the folliwng is the most stable species?

Options

A.
B.
C.
D.

Explanation

To determine which of the given species is the most stable, we need to analyze each compound based on their aromaticity. Here’s a step-by-step solution:

### Step 1: Understand Aromaticity
Aromatic compounds are highly stable due to their unique electronic structure. For a compound to be considered aromatic, it must meet the following criteria:
- It must be cyclic.
- It must be planar.
- It must have a continuous overlap of p-orbitals (conjugation).
- It must contain a specific number of π electrons, following Hückel's rule: \(4n + 2\) π electrons, where \(n\) is a non-negative integer.

Conversely, anti-aromatic compounds, which are less stable, have \(4n\) π electrons and also meet the first three criteria. Non-aromatic compounds do not meet the criteria for aromaticity or anti-aromaticity.

### Step 2: Analyze Each Compound
1. **Compound A**:
- Cyclic: Yes
- Planar: Yes
- Conjugation: Yes
- π Electrons: 6 (which fits \(4n + 2\) for \(n=1\))
- **Conclusion**: Aromatic and stable.

2. **Compound B**:
- Cyclic: Yes
- Planar: Yes
- Conjugation: No
- **Conclusion**: Non-aromatic. Stability is between aromatic and anti-aromatic.

3. **Compound C**:
- Cyclic: Yes
- Planar: No (non-planar structure)
- Conjugation: Yes
- **Conclusion**: Non-aromatic due to non-planarity.

4. **Compound D**:
- Cyclic: Yes
- Planar: No (due to sp³ hybridized carbon)
- Conjugation: Yes
- π Electrons: 8 (which fits \(4n\) for \(n=2\))
- **Conclusion**: Non-aromatic due to non-planarity.

### Step 3: Determine the Most Stable Species
From the analysis:
- Compound A is aromatic and thus the most stable.
- Compound B is non-aromatic.
- Compound C is non-aromatic.
- Compound D is also non-aromatic.

### Final Answer
The most stable species is **Compound A**.

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