Which one of the following C-H bonds is the wekest for homolytic fission ?

Options

A. `CH_(3)-H`
B. `(C_(6)H_(5))CH_(2)-H`
C. `C_(6)H_(5)-H`
D. `(C_(6)H_(5))_(3)C-H`

Explanation

To determine which C-H bond is the weakest for homolytic fission, we need to analyze the stability of the resulting carbon free radicals formed after the bond breaks. The stability of free radicals is influenced by the number of alkyl groups attached to the carbon atom and the presence of resonance.

### Step-by-Step Solution:

1. **Understanding Homolytic Fission**:
- Homolytic fission refers to the breaking of a chemical bond where each atom involved in the bond retains one of the shared electrons, resulting in the formation of two free radicals.

2. **Identifying Free Radical Stability**:
- The stability of carbon free radicals follows a general trend: tertiary > secondary > primary > methyl. This means that the more substituted the carbon atom is, the more stable the free radical will be.

3. **Analyzing the Given Options**:
- We need to evaluate the C-H bonds in the provided options. The options likely include:
- A primary C-H bond
- A secondary C-H bond
- A tertiary C-H bond
- A C-H bond in a compound with resonance (like a phenyl group).

4. **Evaluating Each Option**:
- **Primary C-H Bond**: Forms a primary free radical, which is the least stable.
- **Secondary C-H Bond**: Forms a secondary free radical, which is more stable than a primary free radical.
- **Tertiary C-H Bond**: Forms a tertiary free radical, which is even more stable.
- **C-H Bond with Resonance**: If the bond is attached to a carbon that has resonance (like in a phenyl group), the resulting free radical can be stabilized by resonance, making it very stable.

5. **Conclusion**:
- Since the stability of the free radical is inversely related to the strength of the C-H bond, the weakest C-H bond for homolytic fission will be the one that forms the most stable free radical.
- Therefore, the C-H bond that is part of a structure with multiple phenyl groups (which can delocalize the unpaired electron) will be the weakest.

### Final Answer:
The weakest C-H bond for homolytic fission is the one associated with the carbon that has three phenyl groups attached.

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