Arrange the following logical structures in decreasing order of stability: Option 1) II > I > III Option 2) III > I > II Option 3) II > III > I Option 4) I = II > III

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To determine the stability of the given structures, let's analyze them based on resonance and inductive effects.

Analysis:

Structure (I):

• Conjugated System: Yes.
• Resonance Effect: The positive charge on the carbon can be delocalized through the conjugated system involving the aldehyde group, increasing stability.

Structure (II):

• Conjugated System: Yes.
• Resonance Effect: The lone pair on oxygen is conjugated with the π bond of the carbon-carbon double bond, which stabilizes the structure considerably.

Structure (III):

• Conjugated System: No.
• Hyperconjugation: The lone pair on oxygen is not participating in conjugation due to the presence of a positive charge on oxygen, creating instability.

From this analysis, we can infer that:

• Structure (II) has the highest stability due to resonance stabilization involving oxygen.
• Structure (I) is next in stability because of the delocalized positive charge in the conjugated system.
• Structure (III) is the least stable as it lacks stabilization from resonance or hyperconjugation.

Order of Stability:

$$II > I > III$$

Final Answer: Option 1