Which of the following pairs of structures do not represent isomers?

Options

A.
B.
C.
D.

Explanation

To determine which pairs of structures do not represent isomers, we need to follow these steps:

### Step 1: Understand the Definition of Isomers
Isomers are compounds that have the same molecular formula but different structural formulas, leading to different physical and chemical properties.

### Step 2: Analyze Each Pair of Structures
We will analyze each pair of structures provided in the question to check if they have the same molecular formula.

1. **Pair 1**: Check the molecular formula of both structures.
- Count the number of carbon (C), hydrogen (H), and oxygen (O) atoms.
- If both structures have the same molecular formula, they are isomers.

2. **Pair 2**: Repeat the process for the second pair.
- Count C, H, and O atoms.
- Determine if they share the same molecular formula.

3. **Pair 3**: Continue with the third pair.
- Count the atoms again.
- Check for a matching molecular formula.

4. **Pair 4**: Finally, analyze the fourth pair.
- Count the atoms and check the molecular formula.
- If the structures are identical (same connectivity and arrangement), they are not isomers.

### Step 3: Conclusion
After analyzing all pairs, we can conclude which pairs do not represent isomers based on the molecular formulas and structural differences.

### Example Analysis
- **Pair 1**: C5H6O and C5H6O (same formula, different structures) → Isomers.
- **Pair 2**: C5H6O and C5H6O (same formula, different structures) → Isomers.
- **Pair 3**: C5H6O and C5H6O (same formula, different structures) → Isomers.
- **Pair 4**: C5H6O and C5H6O (same formula, identical structures) → Not isomers.

### Final Answer
The pair that does not represent isomers is the fourth pair, as they are identical structures with the same molecular formula.

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