In which of the following resonance is not possible ?

Options

A. `CH_(2)=C=CH_(2)`
B. `CH_(2)=C=CH^(Theta)`
C. `CH_(2)=C=CH^(o+)`
D. `CH_(2)=C=CH^(*)`

Answer

To determine in which of the given options resonance is not possible, we need to analyze each structure provided in the options. Resonance occurs when there are multiple valid Lewis structures (resonance structures) for a molecule that can be drawn by moving electrons around while keeping the positions of the nuclei fixed.

### Step-by-Step Solution:

1. **Analyze the First Option:**
- The structure has a carbon atom with five bonds.
- Carbon can only form four bonds due to its tetravalency.
- Therefore, this structure cannot exist as it violates the octet rule for carbon.
- **Conclusion:** Resonance is not possible in this structure.

2. **Analyze the Second Option:**
- This structure allows for the movement of electrons.
- We can draw multiple valid resonance structures by shifting the double bonds and lone pairs.
- **Conclusion:** Resonance is possible in this structure.

3. **Analyze the Third Option:**
- This structure also allows for the movement of electrons.
- We can draw multiple valid resonance structures by shifting the double bonds and lone pairs.
- **Conclusion:** Resonance is possible in this structure.

4. **Analyze the Fourth Option:**
- This structure contains a free radical.
- Free radicals can participate in resonance as they can have unpaired electrons that can be delocalized.
- **Conclusion:** Resonance is possible in this structure.

### Final Conclusion:
Based on the analysis, resonance is not possible in the **first option** due to the violation of the tetravalency of carbon, while resonance is possible in the other options.

### Answer:
**Resonance is not possible in the first option.**

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