Which is the most stable carbocation

Options

A. Iso-propyl
B. Triphenylmethyl cation
C. Ethyl cation
D. `pi`-propyl cation

Explanation

To determine the most stable carbocation, we need to analyze the stability of different types of carbocations based on their structure and the surrounding groups. Here’s a step-by-step solution:

### Step 1: Identify the Types of Carbocations
We have several carbocations to consider:
1. Isopropyl cation (CH3)2CHO+
2. Ethyl cation (CH3CH2)+
3. Propyl cation (CH3CH2CH2)+
4. Tri-phenyl cation (C6H5)3C+

### Step 2: Understand Carbocation Stability
Carbocation stability generally increases in the following order:
- Primary (1°) < Secondary (2°) < Tertiary (3°)
This is due to the inductive effect and hyperconjugation provided by alkyl groups.

### Step 3: Analyze Each Carbocation
1. **Isopropyl cation**: This is a secondary carbocation (2°) because it is attached to two alkyl groups.
2. **Ethyl cation**: This is a primary carbocation (1°) as it is attached to only one alkyl group.
3. **Propyl cation**: This is also a primary carbocation (1°).
4. **Tri-phenyl cation**: This is a tertiary carbocation (3°) and is stabilized by resonance from the three phenyl groups. The positive charge can be delocalized over the aromatic rings, significantly increasing stability.

### Step 4: Compare Stability
- The isopropyl cation is more stable than both the ethyl and propyl cations due to being secondary.
- The tri-phenyl cation, being tertiary and having resonance stabilization from three phenyl groups, is more stable than the isopropyl cation.

### Conclusion
The most stable carbocation among those listed is the **tri-phenyl cation (C6H5)3C+** due to its resonance stabilization.

### Final Answer
The most stable carbocation is the tri-phenyl cation (C6H5)3C+.

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