Which of the following pairs of structures is not a pair of resonating structures?

Options

A. `H-C-=overset(o+)NHandH-overset(o+)C=overset(* *)N-H`
B. `CH_(3)-CH=CH-CH_(3)and CH_(3)CH_(2)=CH_(2)`
C. `CH_(3)-underset(O)underset(|)C=CH-underset(O)underset(||)C-CH_(3)andCH_(3)-underset(O)underset(||)C-overset(Ɵ)CH-underset(O)underset(||)O-CH_(3)`
D.

Explanation

To determine which of the given pairs of structures is not a pair of resonating structures, we need to understand the concept of resonance in organic chemistry. Resonance structures are different ways of representing the same molecule, where the arrangement of electrons differs but the arrangement of atoms remains the same.

### Step-by-Step Solution:

1. **Identify Resonating Structures**:
- Look at the pairs of structures provided in the question. For each pair, check if they differ only in the placement of electrons (bonds and lone pairs) while keeping the arrangement of atoms constant.

2. **Check for Valid Resonance**:
- For a pair of structures to be considered resonating structures, they must obey the following rules:
- The structures must have the same number of valence electrons.
- The connectivity of atoms must remain the same.
- Only the electrons (bonds and lone pairs) can be moved, not the atoms.

3. **Analyze Each Pair**:
- For each pair of structures, analyze the movement of electrons:
- If moving electrons results in a change in the connectivity of the atoms, then those structures cannot be considered resonating structures.
- If the movement results in the same connectivity but different electron arrangements, they are valid resonating structures.

4. **Determine the Incorrect Pair**:
- After analyzing all pairs, identify which pair does not meet the criteria for resonance. This will be the pair that shows a change in atom connectivity or does not maintain the same number of valence electrons.

5. **Conclusion**:
- Based on the analysis, select the option that represents the pair of structures that is not a pair of resonating structures.