Which one of the following is most stable

Options

A.
B.
C.
D.

Answer

To determine which of the given compounds is the most stable, we will analyze each option based on the stability of free radicals and the presence of resonance.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- We have four options to analyze, each containing a free radical.

2. **Analyze Option 1**:
- The first compound is cyclobenzene with a free radical on a secondary carbon.
- Stability: Secondary radicals are relatively stable, but they lack resonance stabilization.

**Hint**: Remember that secondary radicals have moderate stability, but resonance can enhance stability.

3. **Analyze Option 2**:
- The second compound is cyclohexene with a free radical.
- Stability: This radical can participate in resonance with the double bond, which increases its stability.

**Hint**: Look for resonance structures; they can significantly increase the stability of radicals.

4. **Analyze Option 3**:
- The third compound has a free radical on a tertiary carbon.
- Stability: Tertiary radicals are more stable than secondary due to hyperconjugation and can also participate in resonance with nearby double bonds or aromatic systems, leading to enhanced stability.

**Hint**: Tertiary radicals are generally the most stable due to hyperconjugation and resonance effects.

5. **Analyze Option 4**:
- The fourth compound has a free radical on a primary carbon.
- Stability: Primary radicals are the least stable due to the lack of hyperconjugation and resonance.

**Hint**: Primary radicals are the least stable; they do not benefit from resonance or hyperconjugation.

6. **Conclusion**:
- After analyzing all four options, the third compound with the free radical on a tertiary carbon is the most stable due to its ability to stabilize through hyperconjugation and resonance.

### Final Answer:
The most stable compound is **Option 3**.