Question

The carbonyl group has following resonating structure.

The correct order of stability of these structures is:

• A. $i)>ii)>iii)$
• B. $iii)>i)>ii)$
• C. $i)>iii)>ii)$
• D. $iii)>ii)>i)$

Answer 1

The correct option is C $i)>iii)>ii)$

The resonating structure with greater number of covalent bond will be most stable since more atom will have the complete octet. Hence (i) is the most sable.
As the negative charge is present on more electronegative oxygen atom and postive charge on more electropositive carbon atom, therefore (iii) is more stable than structure (ii).
Hence the correct stability order becomes $\left(i\right)>\left(iii\right)>\left(ii\right)$.