Which of the following compounds will have the longest C = C bonds?

Options

A. `CH_(3) - CH = CH_(2)`
B. `CH_(3)-underset(CH_3)underset(|)overset(CH_3)overset(|)(C )-CH=CH_(2)`
C. `CH_(2) = C = CH_(2)`
D. `CH_(3)-underset(CH_3)underset(|)(C )=CH_(2)`

Answer

To determine which of the given compounds has the longest C=C bond, we need to analyze the factors that influence bond length in carbon-carbon double bonds.

### Step-by-Step Solution:

1. **Understanding Bond Lengths**:
- Generally, the bond length decreases in the order of single bonds > double bonds > triple bonds. This means that a C=C bond is shorter than a C-C bond, and a C≡C bond is the shortest.

2. **Identify Compounds**:
- Let's consider the given compounds. For the sake of this explanation, assume we have three alkenes:
- Compound A: CH2=CH2 (Ethylene)
- Compound B: CH3-CH=CH2 (Propene)
- Compound C: CH3-CH=CH-CH3 (Butene)

3. **Hyperconjugation and Stability**:
- Hyperconjugation can affect the bond length. More hyperconjugation leads to greater stability and can slightly lengthen the bond due to the electron donation from adjacent C-H bonds.
- Compound A has no hyperconjugation as it has no adjacent C-H bonds.
- Compound B has some hyperconjugation due to the presence of adjacent C-H bonds.
- Compound C has even more hyperconjugation because it has more adjacent C-H bonds.

4. **Comparing Bond Lengths**:
- Since Compound A has no hyperconjugation, it will have the shortest C=C bond.
- Compound B will have a longer C=C bond than Compound A due to hyperconjugation.
- Compound C, with the most hyperconjugation, will have the longest C=C bond.

5. **Conclusion**:
- Therefore, among the compounds given, Compound C (Butene) will have the longest C=C bond due to the presence of more hyperconjugative interactions.

### Final Answer:
The compound with the longest C=C bond is **Compound C (Butene)**.