The most stable free radical is

Options

A.
B.
C.
D.

Answer

To determine the most stable free radical among the given options, we need to analyze the stability factors affecting each free radical. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Free Radicals
We need to look at each option and identify the structure of the free radical present in each compound.

### Step 2: Analyze the Stability Factors
1. **Option 1**: The free radical is adjacent to a double bond, allowing for resonance stabilization. The resonance can delocalize the unpaired electron, making it more stable.

2. **Option 2**: This compound has a free radical next to a double bond and a methyl group (CH3). The methyl group exhibits a +I (inductive) effect, which donates electron density, and the double bond allows for resonance stabilization. Both factors contribute to its stability.

3. **Option 3**: The free radical is on a benzene ring. The sp² hybridized carbon has a higher electronegativity, which makes the free radical less stable due to decreased charge density. There are no significant stabilizing factors here.

4. **Option 4**: Similar to option 3, the free radical is also on an sp² carbon, which is less stable due to its electronegativity. There are no stabilizing factors present.

### Step 3: Compare the Stability
- **Option 1** has resonance stabilization.
- **Option 2** has both resonance and +I effect, making it more stable than option 1.
- **Options 3 and 4** are unstable due to the presence of the free radical on sp² carbons with no stabilizing factors.

### Conclusion
After analyzing all options, **Option 2** is the most stable free radical due to the combined effects of resonance and the +I effect from the methyl group.

### Final Answer
The most stable free radical is **Option 2**.

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