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Relative stability of the contributing structures is : (I) CH2=CH–C(=O)–H (II) CH2=CH–CH(+)=C–H (III) CH2=CH–C(+)=C–H

1. (I) > (III) > (II)
2. (I) > (II) > (III)
3. (II) > (I) > (III)
4. (III) > (II) > (I)

Correct answer: (I) > (II) > (III)

Solution

The correct option reflects the relative stability of the contributing structures based on the degree of substitution and resonance stabilization. Structure (I) is the most stable due to the presence of a carbonyl group that can stabilize the adjacent double bond through resonance, while structure (II) has a positive charge on a secondary carbon, making it less stable than (I) but more stable than (III), which has a positive charge on a primary carbon, leading to the least stability.

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