Which of the following pair constitute resonance structure?

Options

A.
B.
C.
D. `H_(3)C-CH=CH-CH_(3)` and `H_(3)C-CH_(2)-CH=CH_(2)`

Explanation

To determine which pairs constitute resonance structures, we need to understand the concept of resonance in chemistry. Resonance structures are different ways of drawing the same molecule that show the delocalization of electrons. Here’s a step-by-step solution to the question:

### Step 1: Identify the pairs of structures
We need to analyze each pair of structures provided in the question to see if they can be considered resonance structures.

### Step 2: Analyze Pair A
- **Structure 1**: CH3-N^+ (where N has 4 bonds) and O^-
- **Structure 2**: CH3-O=N (double bond between N and O)

In this case, the positions of atoms are changing between the two structures. The nitrogen atom's bonding changes, which means this is not a resonance structure.

**Hint**: Check if the atoms maintain their positions in resonance structures; only electron positions should change.

### Step 3: Analyze Pair B
- **Structure 1**: CH3-C(=O)-CH2^-
- **Structure 2**: CH3-C^-(O^-) (where the negative charge is now on the oxygen)

Here, the negative charge is transferred between the carbon and oxygen while the positions of the atoms remain the same. This indicates that these two structures can be considered resonance structures.

**Hint**: Look for structures where only the electrons are rearranged, and the overall atom arrangement remains unchanged.

### Step 4: Analyze Pair C
- **Structure 1**: CH3-CO-CH3
- **Structure 2**: CH3-C(OH)-CH2

In this case, the position of the hydrogen atom is changing, which means this is not a resonance structure but rather a tautomerization.

**Hint**: Tautomerization involves a change in the position of atoms, unlike resonance structures.

### Step 5: Analyze Pair D
- **Structure 1**: CH3-CH=CH-CH2-CH3
- **Structure 2**: CH3-CH2-CH=CH2

Again, the position of hydrogen atoms is changing, indicating that this is not a resonance structure.

**Hint**: Ensure that the connectivity of atoms remains the same for resonance structures.

### Conclusion
From the analysis, only Pair B constitutes resonance structures. The other pairs involve changes in the positions of atoms, which disqualifies them from being resonance structures.

### Final Answer
**Only Pair B constitutes resonance structures.**