Which of the following is not valid resonance structre of polyene?

Options

A.
B.
C.
D.

Answer

To determine which of the given structures is not a valid resonance structure of a polyene, we need to understand the concept of resonance and the characteristics of valid resonance structures.

### Step-by-Step Solution:

1. **Understanding Polyenes**:
- Polyenes are organic compounds that contain multiple conjugated double bonds. The general structure can be represented as alternating single and double bonds.

2. **Identifying Resonance Structures**:
- Resonance structures are different ways of drawing the same molecule that show the delocalization of electrons. Valid resonance structures must maintain the same connectivity of atoms and only differ in the placement of electrons.

3. **Analyzing Given Structures**:
- We need to analyze each of the provided structures to see if they can be considered valid resonance forms.
- A valid resonance structure should not have any atoms with an incomplete octet (except for certain exceptions like hydrogen), and it should not have two identical charges (like two negative charges) on adjacent atoms.

4. **Evaluating Each Option**:
- **Option A**: Check if it maintains the same connectivity and has valid charge distribution.
- **Option B**: Same as above, ensure that it does not have charges that violate resonance rules.
- **Option C**: Evaluate for proper charge placement and connectivity.
- **Option D**: This is where we need to be careful. If this structure shows two negative charges on adjacent atoms, this is not a valid resonance structure.

5. **Conclusion**:
- After evaluating the options, we find that **Option D** is the structure that is not a valid resonance structure of polyene because it has two negative charges that cannot coexist on adjacent atoms, making it unstable.

### Final Answer:
The option that is not a valid resonance structure of polyene is **Option D**.