Which among the following is most stable carbonation

Options

A. iso - propyl
B. Triphenylmethyl cation
C. Ethyl cation
D. t - Butyl cation

Answer

To determine which among the given options is the most stable carbocation, we need to analyze the stability of each carbocation based on the number of alkyl groups and resonance effects.

### Step-by-Step Solution:

1. **Understanding Carbocation Stability**:
- Carbocation stability increases with the number of alkyl groups attached to the positively charged carbon. This is because alkyl groups can donate electron density through inductive effects, stabilizing the positive charge.
- Additionally, resonance can significantly enhance stability. Carbocations that can delocalize their positive charge through resonance with adjacent π systems (like benzene rings) are more stable.

2. **Analyzing Each Carbocation**:
- **Isopropyl Carbocation**: This is a secondary carbocation (2°) with the structure:
\[ \text{(CH}_3\text{)}_2\text{C}^+\text{H} \]
It has two alkyl groups, which provides some stability, but it is less stable than tertiary carbocations or carbocations with resonance.

- **Benzylic Carbocation**: This carbocation has the structure:
\[ \text{C}_6\text{H}_5\text{CH}_2^+ \]
The positive charge is adjacent to a benzene ring, allowing for resonance stabilization. This makes it more stable than the isopropyl carbocation.

- **Triphenylmethyl Carbocation**: The structure is:
\[ \text{C}^+(\text{C}_6\text{H}_5)_3 \]
This carbocation has three phenyl groups attached to the positively charged carbon. The positive charge can be delocalized over the three benzene rings, providing significant resonance stabilization, making it extremely stable.

- **Ethyl Carbocation**: This is a primary carbocation (1°) with the structure:
\[ \text{C}_2\text{H}_5^+ \]
It has no resonance stabilization and is the least stable among the options.

- **Tertiary Butyl Carbocation**: This carbocation has the structure:
\[ \text{(CH}_3\text{)}_3\text{C}^+ \]
It is a tertiary carbocation (3°) and is stable due to the presence of three alkyl groups. However, it lacks the resonance stabilization present in the triphenylmethyl carbocation.

3. **Conclusion**:
- Comparing all the carbocations, the **triphenylmethyl carbocation** is the most stable due to the extensive resonance stabilization provided by the three phenyl groups.

### Final Answer:
The most stable carbocation among the given options is the **triphenylmethyl carbocation**.