Question

The order of relative stability of the contributing structure is:

Choose the correct answer from the options given below:

• A. $I >II >III$
• B. $II >I >III$
• C. $I = II = III$
• D. $III >II >I$

Answer 1

The Correct Option is A

The question involves evaluating the relative stability of resonance structures. The stability of resonance structures mainly depends on the following factors: 

1. Octet Rule: Structures in which all atoms, especially the second-period elements (like C, N, O), have a complete octet are generally more stable.
2. Charge Separation: Structures with minimal charge separation are more stable. A neutral structure is more stable than a charged one.
3. Negative Charge on Electronegative Atoms: Structures that place negative charges on more electronegative atoms (like oxygen) are more stable.
4. Positive Charge on Electropositive Atoms: Structures with positive charges on less electronegative atoms are more stable.

Analyzing the given resonance structures:

1. Structure I: This structure has all atoms with complete octet shells and no charge separation, which makes it the most stable.
2. Structure II: This structure has a positive charge on a carbon atom and a negative charge on an oxygen atom. There is charge separation, reducing its stability compared to structure I, but the charges are on appropriate atoms considering electronegativity.
3. Structure III: This structure has carbon with a negative charge and oxygen with a positive charge, which is the least favorable distribution of charges among the given structures. This increases its instability compared to the other structures.

Based on the above analysis, the order of relative stability is:

\(I > II > III\)

Answer 2

Structure I is the most stable because it is a neutral resonating structure. In general, neutral structures are more stable compared to charged structures.

Structure II is less stable than I because it involves a positive charge on a less electronegative atom compared to structure III. However, it is more stable than III because the negative charge in III is on a carbon atom, making it the least stable due to charge separation.

Structure III is the least stable among the three due to the presence of a negative charge on carbon and overall charge separation, making it highly unstable.
The Correct answer is: \(I >II >III\)