Which of the following pairs has higher resonance energy :
`CH_(2) = CH - OH " and " CH_(2)= CH - CH = CH - OH `

Answer

To determine which of the two compounds has higher resonance energy, we need to analyze the resonance structures of each compound.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Compound 1: CH₂=CH-OH
- Compound 2: CH₂=CH-CH=CH-OH

2. **Draw the Resonance Structures for Compound 1 (CH₂=CH-OH)**:
- The double bond between the first two carbon atoms can participate in resonance with the hydroxyl group (OH).
- The lone pair of electrons on the oxygen can shift to form a double bond with the carbon, while the double bond between the two carbon atoms shifts to the adjacent carbon.
- The resonance structure can be represented as:
- **Structure 1**: CH₂=CH-OH
- **Structure 2**: CH₂-CH(OH)⁻ (where the oxygen carries a positive charge)

This compound has a limited number of resonance structures (only one significant structure).

3. **Draw the Resonance Structures for Compound 2 (CH₂=CH-CH=CH-OH)**:
- In this compound, the double bonds can interact with the hydroxyl group, allowing for multiple resonance structures.
- The lone pair on the oxygen can shift to form a double bond with the adjacent carbon, while the double bond between the carbon atoms can shift as well.
- Possible resonance structures include:
- **Structure 1**: CH₂=CH-CH=CH-OH
- **Structure 2**: CH₂-CH(OH)⁻-CH=CH⁺ (where the oxygen carries a positive charge)
- **Structure 3**: CH₂=CH-CH(OH)⁻-CH=CH⁺ (and other variations)

This compound has multiple resonance structures, indicating a higher extent of resonance.

4. **Compare the Extent of Resonance**:
- Compound 1 has limited resonance structures (only 1 significant structure).
- Compound 2 has multiple resonance structures, allowing for greater delocalization of electrons.

5. **Determine Resonance Energy**:
- Resonance energy is directly related to the extent of resonance. The more resonance structures a compound has, the higher the resonance energy.
- Since Compound 2 has more resonance structures than Compound 1, it will have higher resonance energy.

### Conclusion:
- **Compound 2 (CH₂=CH-CH=CH-OH)** has higher resonance energy compared to **Compound 1 (CH₂=CH-OH)**.