Question 23.9: Draw the electron-dot structure that results from the curved......
Draw the electron-dot structure that results from the curved arrows shown below. If an incorrect structure results, explain why. For valid structures give the line drawing and indicate which resonance structure is preferred based on formal charge.
STRATEGY
Draw the complete electron-dot structure by adding hydrogen atoms and lone pairs. Then rearrange electrons as indicated by the curved arrows and check to make sure that the octet rule is not exceeded. Assign formal charges and evaluate the best structure based upon criteria given in Section 7.10 and summarized below.
• Smaller formal charges (either positive or negative) are preferable to larger ones. Zero is preferred over -1, but -1 is preferred over -2.
• Negative formal charges should reside on more electronegative atoms.
• Like charges should not be on adjacent atoms.
(a) The resonance structure on the left is preferred because the negative formal charge is on the more electronegative oxygen atom.
(b) Arrow results in an incorrect electron-dot structure because carbon cannot have five bonds.
(c) The resonance structure on the left is preferred since formal charge on all atoms is zero. Energy is required to separate + and – charges, so the structure without formal charges is probably lower in energy than the structure with formal charges.
(d) Arrow results in an incorrect electron-dot structure because carbon cannot have five bonds.
