In which of the following pairs, indicated bond is of greater strength :
`CH_(2) = CH underset(uarr" ")-CH = CH_(2) " and " CH_(2) = CHunderset(uarr" ")-CH_(2) - CH_(3)`

Answer

To determine which indicated bond is of greater strength in the given pairs, we need to analyze the structures and the nature of the bonds involved.

### Step-by-Step Solution:

1. **Identify the Structures**:
- For the first compound: `CH2=CH-CH=CH2`
- For the second compound: `CH2=CH-CH2-CH3`

2. **Visualize the Bonds**:
- In the first compound, we have a double bond between the first two carbon atoms and another double bond between the last two carbon atoms.
- In the second compound, we have a double bond between the first two carbon atoms and a single bond between the second and third carbon atoms.

3. **Analyze the Bonds**:
- In the first compound, the double bond can participate in resonance. The double bond between the first and second carbon can shift to the second and third carbon due to resonance. This resonance can stabilize the structure and increase the effective bond strength of the C-C single bond in this case.
- In the second compound, the bond between the second and third carbon is a single bond and does not have resonance stabilization.

4. **Compare Bond Strengths**:
- The presence of resonance in the first compound allows for greater bond strength due to the delocalization of electrons.
- The second compound lacks this resonance effect, making the single bond relatively weaker.

5. **Conclusion**:
- Therefore, the bond indicated in the first compound (`CH2=CH-CH=CH2`) is stronger than the bond indicated in the second compound (`CH2=CH-CH2-CH3`).

### Final Answer:
The bond in the first pair (`CH2=CH-CH=CH2`) is of greater strength than the bond in the second pair (`CH2=CH-CH2-CH3`).

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