The most stable radical among the following is :

Options

A. `{:(CH_(2)-CH_(2)^(*)),(|),(NO_(2)):}`
B. `{:(CH_(2)-CH_(2)^(*)),(|),(COO^(-)):}`
C. `{:(C_(2)-CH_(2)^(*)),(|),(CH_(3)):}`
D. `{:(CH_(2)-CH_(2)^(*)),(|),(O^(-)):}`

Answer

To determine the most stable radical among the given options, we need to analyze the nature of the substituents attached to each radical and their effects on stability.

### Step-by-Step Solution:

1. **Identify the radicals**: We have four radicals to consider. Let's denote them as:
- Radical A
- Radical B
- Radical C
- Radical D

2. **Understand radical stability**: Free radicals are species with an unpaired electron. Their stability is influenced by the presence of substituents that can either donate or withdraw electron density. Electron-donating groups (EDGs) can stabilize radicals, while electron-withdrawing groups (EWGs) can destabilize them.

3. **Analyze the substituents**:
- **Radical A**: Contains an electron-withdrawing group (e.g., NO2 or COO-).
- **Radical B**: Contains an electron-withdrawing group (e.g., NO2 or COO-).
- **Radical C**: Contains an electron-donating group (e.g., CH3).
- **Radical D**: Contains an electron-donating group (e.g., O-CH3).

4. **Evaluate the effects of substituents**:
- For **Radicals A and B**: The presence of electron-withdrawing groups (NO2 or COO-) will destabilize the radicals due to the -I effect, which pulls electron density away from the radical center.
- For **Radical C (CH3)**: The methyl group (CH3) is an electron-donating group, but it is not as effective as other groups in stabilizing radicals.
- For **Radical D (O-CH3)**: The methoxy group (O-CH3) has an oxygen atom that can donate electron density more effectively than a carbon atom. The oxygen has a lone pair of electrons that can help stabilize the radical.

5. **Conclusion**: Among the radicals analyzed, Radical D (O-CH3) is the most stable due to the strong electron-donating ability of the oxygen atom, which stabilizes the unpaired electron in the radical.

### Final Answer:
The most stable radical among the given options is **Radical D (O-CH3)**.

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