Which of the following is the most stable?

Options

A. `PH_(3)C^(+)`
B. `Ph_(2)overset(+)CH`
C. `Phoverset(+)CH_(2)`
D. Tropylium cation

Explanation

To determine which of the given compounds is the most stable carbocation, we will analyze the stability of each carbocation based on their structure and the concept of aromaticity and conjugation.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four compounds to analyze for carbocation stability. Let's denote them as Compound A, Compound B, Compound C, and Compound D.

2. **Recall the Order of Carbocation Stability**: The stability of carbocations generally follows this order:
- Aromatic carbocations > Conjugated carbocations > Tertiary (3°) carbocations > Secondary (2°) carbocations > Primary (1°) carbocations.

3. **Analyze Compound A**:
- Structure: C, Ph, Ph, Ph (where Ph represents a phenyl group).
- This compound has three phenyl groups attached to the carbocation center, allowing for significant resonance stabilization through conjugation.
- Stability: This is a conjugated carbocation with 3 phenyl groups, making it relatively stable.

4. **Analyze Compound B**:
- Structure: Ph, C, H (with a carbocation).
- This compound has two phenyl groups attached to the carbocation.
- Stability: It has less resonance stabilization compared to Compound A.

5. **Analyze Compound C**:
- Structure: Ph, C, H2+ (with a carbocation).
- This compound has only one phenyl group attached to the carbocation.
- Stability: It has the least resonance stabilization among the first three compounds.

6. **Analyze Compound D (Propellium Ion)**:
- Structure: A seven-carbon structure with a carbocation.
- This compound is planar and has alternating double bonds, allowing for extensive resonance and satisfying Huckel's rule (4n + 2 π electrons).
- Stability: This compound is aromatic, which makes it the most stable due to the aromaticity of the carbocation.

7. **Conclusion**: Based on the analysis, the most stable carbocation is the one that is aromatic. Therefore, Compound D (Propellium Ion) is the most stable carbocation.

### Final Answer:
The most stable carbocation is **Compound D (Propellium Ion)**.

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