`(I) CH_(2) = CH - CH = CH_(2)`
`(II) overset(Theta)CH_(2) - CH = CH - overset(o+)CH_(2)`
`(III) overset(o+)CH_(2) - CH = CH - overset(Theta)CH_(2)`
Among, these, which are canonical structures ?

Options

A. I and II
B. I and III
C. II and III
D. all

Answer

To determine which of the given structures are canonical (or resonance) structures, we need to analyze each structure and see if they can be interconverted through the movement of electrons (specifically, pi electrons and lone pairs) without breaking any sigma bonds.

### Step-by-Step Solution:

1. **Identify the Structures:**
- Structure (I): \( CH_2 = CH - CH = CH_2 \)
- Structure (II): \( \overset{+}{CH_2} - CH = CH - \overset{0}{CH_2} \)
- Structure (III): \( \overset{0}{CH_2} - CH = CH - \overset{+}{CH_2} \)

2. **Draw the Lewis Structures:**
- For Structure (I), we have a linear diene with alternating double bonds.
- For Structure (II), there is a positive charge on one end and a neutral carbon in the middle.
- For Structure (III), there is a positive charge on the opposite end compared to Structure (II).

3. **Check for Resonance:**
- **From Structure (I) to Structure (II):**
- Move the double bond between the first and second carbon to the second and third carbon, while placing a positive charge on the first carbon. This transformation is valid as it involves the movement of pi electrons.
- **From Structure (II) to Structure (III):**
- Move the double bond from the second and third carbon to the first and second carbon, while placing a positive charge on the third carbon. This is also a valid transformation.
- **From Structure (III) back to Structure (I):**
- Move the double bond from the first and second carbon to the second and third carbon, which returns us to Structure (I).

4. **Conclusion:**
- Since we can interconvert Structures (I), (II), and (III) through the movement of electrons without breaking any sigma bonds, all three structures are canonical (resonance) structures of each other.

### Final Answer:
All three structures (I), (II), and (III) are canonical structures.