Which carbocation is most stable

Options

A.
B.
C.
D.

Answer

To determine which carbocation is the most stable among the given options, we can follow these steps:

### Step 1: Identify the Types of Carbocations
- **Carbocations** are positively charged carbon species. Their stability is influenced by the degree of substitution (primary, secondary, tertiary) and resonance.
- **Primary (1°)** carbocations have one alkyl group attached.
- **Secondary (2°)** carbocations have two alkyl groups attached.
- **Tertiary (3°)** carbocations have three alkyl groups attached.

### Step 2: Analyze Each Option
1. **First Option**: This carbocation is a **secondary carbocation** with resonance stabilization. The presence of resonance means that the positive charge can be delocalized, increasing stability.

2. **Second Option**: This carbocation is a **secondary carbocation** but lacks resonance stabilization. It is also sp hybridized, which is less stable due to the higher s-character of the orbital holding the positive charge.

3. **Third Option**: This carbocation is a **primary carbocation**. Primary carbocations are the least stable due to having only one alkyl group to help stabilize the positive charge.

4. **Fourth Option**: This option is identical to the second option, being a secondary carbocation without resonance.

### Step 3: Compare Stability
- **Tertiary > Secondary (with resonance) > Secondary (without resonance) > Primary**
- The first option has resonance and is a secondary carbocation, making it the most stable.
- The second and fourth options are less stable due to lack of resonance, and the third option is the least stable.

### Conclusion
The most stable carbocation is the **first option**, which is a secondary carbocation with resonance stabilization.

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