Question

which of the following is/are the most significant resonance structure(s) (which contributes the most the overall resonance hybrid)? a. i b. ii c. iii d. iv

Explanation:

Step1: Analyze resonance rules

The most significant resonance structure has the least separation of formal charges, complete octets on more electronegative atoms, and the most stable distribution of charge.

Step2: Evaluate each structure

• Structure I: Has a positive charge on a carbon adjacent to an oxygen with lone - pairs.
• Structure II: Has the positive charge delocalized onto the oxygen, which is more electronegative than carbon. This is a more stable resonance form as the electronegative oxygen can better accommodate a positive charge compared to carbon in some cases due to its ability to attract electrons.
• Structure III: Has two adjacent positive charges, which is highly unstable.
• Structure IV: Has the positive charge on a terminal carbon, which is less stable compared to having it on the oxygen.

Answer:

B. II