Least stable carbocation among the following is

Options

A.
B.
C.
D.

Answer

To determine the least stable carbocation among the given options, we need to analyze the stability of each carbocation based on factors such as resonance, inductive effects, and hyperconjugation. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Carbocations
We have four carbocations to analyze. Let's denote them as:
1. Carbocation A
2. Carbocation B
3. Carbocation C
4. Carbocation D

### Step 2: Analyze Carbocation A
- **Structure**: Benzene ring with a carbocation attached to a carbon that has a methyl group (CH3).
- **Stability Factors**:
- Resonance: The positive charge can be delocalized through the benzene ring.
- Inductive Effect: The methyl group (+I effect) can slightly stabilize the carbocation.
- **Conclusion**: Carbocation A is relatively stable due to resonance and inductive effects.

### Step 3: Analyze Carbocation B
- **Structure**: Similar to Carbocation A but with a different arrangement.
- **Stability Factors**:
- Resonance: The positive charge can be delocalized through the benzene ring.
- Inductive Effect: The presence of methyl groups also contributes to stability.
- **Conclusion**: Carbocation B is also relatively stable due to resonance and inductive effects.

### Step 4: Analyze Carbocation C
- **Structure**: A tertiary carbocation with three methyl groups attached.
- **Stability Factors**:
- Inductive Effect: The three methyl groups provide a strong +I effect.
- Hyperconjugation: There are many adjacent C-H bonds that can stabilize the positive charge.
- **Conclusion**: Carbocation C is the most stable due to strong inductive effects and hyperconjugation.

### Step 5: Analyze Carbocation D
- **Structure**: A carbocation with a double bond and a positive charge on a carbon adjacent to a carbon with a double bond.
- **Stability Factors**:
- Resonance: There is some resonance, but it is limited.
- Inductive Effect: The presence of the double bond can exert a -I effect, which destabilizes the carbocation.
- **Conclusion**: Carbocation D is the least stable due to the destabilizing -I effect and limited resonance.

### Final Conclusion
After analyzing all four carbocations, we find that **Carbocation D** is the least stable due to the presence of a -I effect from the double bond and limited resonance stabilization.

### Answer
The least stable carbocation among the following is **Carbocation D**.

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