Which of the following resonance structures of the acetate ion (CH3COO-) is more significant?

• A. The structure in which the negative charge is placed on the carbon atom.
• B. The structure in which both oxygen atoms share the negative charge equally, with a double bond between carbon and one oxygen and a single bond between carbon and the other oxygen, and resonance arrows between them.
• C. The structure in which the negative charge is localized entirely on one oxygen atom, with a double bond between carbon and the other oxygen.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the concept of resonance structures. Resonance structures are different Lewis structures for the same molecule that show the delocalization of electrons. The actual molecule is a hybrid of these structures, and the more stable resonance contributors contribute more to the hybrid.
2. Step 2: Analyze the resonance structures of the acetate ion (CH3COO-). The acetate ion has two oxygen atoms bonded to the central carbon atom. The negative charge can be delocalized between the two oxygen atoms through resonance, involving a double bond alternating between the two oxygens.
3. Step 3: Evaluate the stability of each resonance structure. Structures where the negative charge is placed on more electronegative atoms (oxygen rather than carbon) are generally more stable. Also, resonance structures that minimize formal charges and place negative charges on oxygen atoms are favored.
4. Step 4: Compare the given options: (a) negative charge on carbon, (b) negative charge shared equally between oxygens with resonance, and (c) negative charge localized on one oxygen. The resonance structure with the negative charge delocalized over both oxygens (option b) is more stable because it distributes the charge and involves resonance stabilization.
5. Step 5: Conclude that the most significant resonance contributor is the one where the negative charge is shared equally between the two oxygen atoms, with resonance arrows indicating electron delocalization, rather than localized on carbon or on a single oxygen.