In which of the following pairs is the sturcture on the right major resonance contributor?

Options

A.
B.
C.
D.

Explanation

To determine which structure in each pair is the major resonance contributor, we need to analyze the resonance structures based on certain stability criteria. Here's a step-by-step solution:

### Step 1: Identify the Resonance Structures
For each pair given in the question, identify the resonance structures. Look for lone pairs, double bonds, and charges (positive or negative) in the structures.

### Step 2: Evaluate the Resonance Contributors
1. **Neutral vs. Ionic**: Generally, neutral structures are more stable than ionic structures. If one structure is neutral and the other is ionic, the neutral structure is likely the major contributor.

2. **Charge Distribution**: If both structures are ionic, the one with the charge on the more electronegative atom is more stable. Conversely, if the charge is on a less electronegative atom, that structure is less stable.

3. **Aromaticity**: If one of the structures is aromatic, it is usually the major contributor due to the added stability from resonance and delocalization of electrons.

### Step 3: Apply the Criteria to Each Pair
- For each pair, apply the criteria mentioned above:
- Compare the stability of neutral vs. ionic structures.
- Check the placement of charges and electronegativity.
- Look for any aromatic structures.

### Step 4: Conclude the Major Contributor
After evaluating each pair based on the above criteria, conclude which structure on the right is the major resonance contributor.

### Example Analysis
1. **Pair 1**:
- Left Structure: Neutral
- Right Structure: Ionic
- Conclusion: Right structure is not the major contributor (Left is major).

2. **Pair 2**:
- Left Structure: Neutral
- Right Structure: Ionic
- Conclusion: Right structure is not the major contributor (Left is major).

3. **Pair 3**:
- Left Structure: Neutral
- Right Structure: Aromatic
- Conclusion: Right structure is the major contributor due to aromaticity.

### Final Answer
Based on the analysis, the structure on the right is the major resonance contributor in the pair where it is aromatic.

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