The most stable free radical among the following is

Options

A.
B.
C.
D.

Answer

To determine the most stable free radical among the given options, we need to analyze the stability of each free radical based on the following principles:

1. **Degree of Substitution**: Free radicals are more stable when they are more substituted. Tertiary (3°) radicals are more stable than secondary (2°), which are more stable than primary (1°), and methyl radicals are the least stable.

2. **Resonance Stabilization**: Free radicals that can delocalize their unpaired electron through resonance are more stable than those that cannot.

3. **Hyperconjugation**: The presence of adjacent C-H bonds can stabilize free radicals through hyperconjugation.

### Step-by-Step Solution:

**Step 1: Identify the Types of Free Radicals**
- Examine each option to identify whether they are primary, secondary, or tertiary radicals, and check if they have resonance stabilization.

**Step 2: Analyze Each Free Radical**
- **Option A**: This is a primary free radical. It has no resonance stabilization and is the least stable.
- **Option B**: This is a secondary free radical. It has some resonance stabilization but is less stable than a tertiary radical.
- **Option C**: This is a tertiary free radical. It is more stable than both primary and secondary radicals due to hyperconjugation and the inductive effect from surrounding alkyl groups.
- **Option D**: This free radical is resonance-stabilized. It can delocalize the unpaired electron, making it more stable than the others.

**Step 3: Compare Stability Factors**
- Compare the degree of substitution and resonance stabilization:
- Tertiary radicals (Option C) are generally more stable than secondary (Option B) and primary (Option A).
- If Option D has significant resonance stabilization, it may surpass the stability of a tertiary radical.

**Step 4: Conclusion**
- After analyzing all options, if Option D has both resonance stabilization and a high degree of substitution, it would be the most stable free radical among the given choices.

### Final Answer:
The most stable free radical among the given options is **Option D**.