Carbocations may be stabilised by :

Options

A. `pi`-bonds only at phenylic position
B. `pi`-bonds only at phenylic position
C. `pi`-bonds at allylic and benzylic position also
D. `-I` effect

Explanation

To solve the question on how carbocations can be stabilized, we can break down the stabilization mechanisms step by step.

### Step 1: Understanding Carbocations
Carbocations are positively charged carbon species that are electron deficient. Their stability is crucial in organic chemistry, as it influences reaction mechanisms and pathways.

**Hint:** Remember that carbocations are electron-deficient, which means they need stabilization from electron-rich species.

### Step 2: Identifying Stabilization Mechanisms
Carbocations can be stabilized through resonance and hyperconjugation. We will explore different positions where carbocations can be formed and how they can be stabilized.

**Hint:** Think about how resonance structures can redistribute charge and stabilize the positive charge.

### Step 3: Stabilization by Resonance
1. **Benzylic Position**: A carbocation at the benzylic position (next to a benzene ring) can be stabilized through resonance. The positive charge can delocalize into the aromatic ring, forming resonance structures.

**Hint:** Look for structures where the positive charge can interact with pi electrons from adjacent double bonds.

2. **Allylic Position**: Similarly, an allylic carbocation (adjacent to a double bond) can also be stabilized by resonance. The double bond can shift, allowing the positive charge to be shared across multiple atoms.

**Hint:** Consider how moving a double bond can create different resonance forms that stabilize the positive charge.

### Step 4: Evaluating Other Positions
3. **Vinylic Position**: A carbocation at the vinylic position (directly on a double bond) is not stabilized by resonance because the positive charge cannot be delocalized effectively.

**Hint:** Recall that for effective resonance, the positive charge must be adjacent to a pi bond that can participate in resonance.

4. **Phenolic Position**: A carbocation at the phenolic position (directly on the aromatic ring) is also not effectively stabilized by resonance in the same way as benzylic or allylic carbocations.

**Hint:** Think about how the structure of the aromatic ring affects the ability of the positive charge to be stabilized.

### Step 5: Considering Inductive Effects
5. **Inductive Effect**: The -I effect (negative inductive effect) refers to the withdrawal of electron density through sigma bonds. Since carbocations are already electron deficient, any further withdrawal of electrons will destabilize them.

**Hint:** Remember that electron-withdrawing groups will not stabilize a positively charged species.

### Conclusion
From the analysis, we conclude that carbocations can be stabilized primarily through resonance at the benzylic and allylic positions. The correct answer to the question is that carbocations are stabilized by resonance, particularly in the benzylic and allylic positions.

**Final Answer:** Carbocations may be stabilized by resonance at the benzylic and allylic positions.