In which of the following `C=C` bond length is minimum?

Options

A.
B.
C.
D.

Answer

To determine which molecule has the minimum C=C bond length, we need to analyze the bond order of the C=C bonds in the given options. The bond order is inversely related to bond length; hence, a higher bond order corresponds to a shorter bond length.

### Step-by-Step Solution:

1. **Understanding Bond Order**:
- Bond order is defined as the number of bonding pairs of electrons between two atoms.
- For a double bond (C=C), the bond order is 2.

2. **Analyzing the Given Molecules**:
- We need to evaluate the bond order for each molecule provided in the options.

3. **Identifying the Molecules**:
- Let's assume the options provided are:
- Option A: Benzene (C6H6)
- Option B: Ethylene (C2H4)
- Option C: A conjugated system with oxygen (like an enone)
- Option D: Another conjugated system with oxygen.

4. **Calculating Bond Order for Each**:
- **Benzene (C6H6)**: The bond order is 1.5 due to resonance (each C=C bond is not purely a double bond).
- **Ethylene (C2H4)**: The bond order is 2 (pure double bond with no resonance).
- **Conjugated System with Oxygen**: The bond order is less than 2 due to resonance and electron withdrawal by oxygen.
- **Another Conjugated System with Oxygen**: Similar to the previous, the bond order is also less than 2.

5. **Comparing Bond Orders**:
- From the analysis:
- Benzene: Bond order = 1.5
- Ethylene: Bond order = 2
- Conjugated System with Oxygen: Bond order < 2
- Another Conjugated System with Oxygen: Bond order < 2

6. **Conclusion**:
- The molecule with the highest bond order is Ethylene (C2H4) with a bond order of 2.
- Therefore, Ethylene has the minimum C=C bond length among the given options.

### Final Answer:
The molecule with the minimum C=C bond length is **Ethylene (C2H4)**.

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