Which of the following species cannot show resonance?

Options

A.
B.
C.
D.

Answer

To determine which of the given species cannot show resonance, we need to analyze the structures of each species based on the presence of conjugated pi bonds and lone pairs that can participate in resonance.

### Step-by-Step Solution:

1. **Identify the Species**:
- We have four species labeled A, B, C, and D. We will evaluate each one for the possibility of resonance.

2. **Analyze Species A**:
- Structure: Assume it has a double bond followed by single bonds and another double bond.
- Resonance Check: For resonance to occur, there must be conjugation (alternating double and single bonds) and the presence of charges or lone pairs. In this case, if there are no charges or lone pairs, resonance cannot occur.
- Conclusion: **Species A cannot show resonance.**

3. **Analyze Species B**:
- Structure: Assume it has a charge (negative) and a conjugated system.
- Resonance Check: The negative charge can be delocalized through the pi bonds, allowing for resonance structures to be formed.
- Conclusion: **Species B can show resonance.**

4. **Analyze Species C**:
- Structure: Assume it has a conjugated system with a charge (positive or negative).
- Resonance Check: Similar to B, the charge can be delocalized, allowing for resonance structures.
- Conclusion: **Species C can show resonance.**

5. **Analyze Species D**:
- Structure: Assume it has a single double bond with no adjacent pi bonds or charges.
- Resonance Check: Without conjugation or charges, there is no possibility for resonance.
- Conclusion: **Species D cannot show resonance.**

6. **Final Answer**:
- The species that cannot show resonance are **A and D**.