Which of the following best describes the resonance hybrid of the acetate ion ${\mathrm{CH}}_3{\mathrm{COO}}_{-}$?

• A. A structure in which one oxygen atom has a double bond to carbon and the other has a single bond with a negative charge.
• B. A structure in which both carbon-oxygen bonds are equivalent and the negative charge is delocalized over both oxygen atoms.
• C. A structure in which the negative charge is on the carbon atom.
• D. A structure in which the negative charge is localized entirely on one oxygen atom.

Answer: (B)

Verified step by step guidance

1. Identify the resonance structures of the acetate ion (CH\_3COO\textsuperscript{\textminus}). The acetate ion has two major resonance contributors where the negative charge and double bond are distributed between the two oxygen atoms bonded to the carbonyl carbon.
2. Draw each resonance structure showing one oxygen atom double-bonded to the carbon and the other oxygen atom single-bonded with a negative charge. Then, draw the second resonance structure with the positions of the double bond and negative charge swapped between the two oxygens.
3. Understand that the resonance hybrid is a weighted average of these resonance structures, meaning the actual molecule does not switch between these forms but rather has characteristics of both simultaneously.
4. Recognize that in the resonance hybrid, the two carbon-oxygen bonds are equivalent in length and strength, intermediate between a single and double bond, due to delocalization of electrons.
5. Conclude that the negative charge is not localized on one oxygen atom but is delocalized over both oxygen atoms, stabilizing the acetate ion and making the two C–O bonds equivalent.