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: Recall resonance - stability rules

The most significant resonance structure has the least separation of formal charges, and the more electronegative atoms should bear the negative charge (if any). Also, structures with full - octet atoms are more stable.

Step2: Analyze each structure

In structure I, the positive charge is on a carbon atom adjacent to an oxygen atom with lone - pairs. In structure II, the positive charge is delocalized, and the oxygen atom has a positive charge which is less favorable as oxygen is more electronegative. In structure III, there is a separation of charges and the oxygen has a positive charge. In structure IV, the positive charge is on the terminal carbon, and there is no resonance stabilization from the oxygen lone - pairs as effectively as in structure I. Structure I has the positive charge on a carbon atom, and the oxygen can donate its lone - pairs to stabilize the positive charge through resonance while maintaining full - octet on all atoms.

Answer:

A. I