Correct stability order of the given free radicals is

Options

A.
B.
C.
D.

Answer

To determine the correct stability order of the given free radicals, we need to analyze the structure and the effects of substituents on the stability of each radical. Here's a step-by-step breakdown of the solution:

### Step 1: Identify the Free Radicals
We start by identifying the free radicals provided in the question. Let's denote them as follows:
1. Free Radical 1: CH3-CH2• (Ethyl Radical)
2. Free Radical 2: Benzyl Radical (C6H5-CH2•)
3. Free Radical 3: CH3-C(CH3)•-CH3 (Tertiary Radical)
4. Free Radical 4: CH3-CH(CH3)•-CH3 (Secondary Radical)

### Step 2: Analyze the Stability Factors
The stability of free radicals can be influenced by resonance and inductive effects:
- **Resonance (R effect)**: Stabilizes the radical by delocalizing the unpaired electron.
- **Inductive Effect (I effect)**: Alkyl groups can donate electron density through the sigma bond, stabilizing the radical.

### Step 3: Evaluate Each Free Radical
1. **Ethyl Radical (CH3-CH2•)**:
- Has no resonance stabilization.
- Inductive effect from the CH3 group is present but minimal.
- Stability: Least stable.

2. **Benzyl Radical (C6H5-CH2•)**:
- Exhibits resonance stabilization as the unpaired electron can be delocalized into the aromatic ring.
- Stability: More stable than the ethyl radical.

3. **Tertiary Radical (CH3-C(CH3)•-CH3)**:
- Has three methyl groups providing significant inductive effect.
- No resonance but the inductive effect is strong.
- Stability: More stable than the benzyl radical due to the inductive effect.

4. **Secondary Radical (CH3-CH(CH3)•-CH3)**:
- Has two methyl groups providing inductive stabilization.
- Less stable than the tertiary radical but more stable than the ethyl radical.
- Stability: Intermediate stability.

### Step 4: Establish the Stability Order
Based on the analysis:
- Tertiary Radical (most stable)
- Benzyl Radical
- Secondary Radical
- Ethyl Radical (least stable)

### Final Stability Order
Thus, the correct order of stability for the given free radicals is:
**Tertiary Radical > Benzyl Radical > Secondary Radical > Ethyl Radical**