A student is investigating why acetic acid (CH₃COOH) is a stronger acid than ethanol (CH₃CH₂OH). The conjugate base of acetic acid has the empirical formula C₂H₃O₂⁻ and exhibits two identical C–O bond lengths of 126 pm.
The student proposes two nonequivalent Lewis diagrams for C₂H₃O₂⁻.
• Diagram A: The central carbon atom is double-bonded to one oxygen atom and single-bonded to the second oxygen atom, with the negative charge localized on the single-bonded oxygen.
• Diagram B: The central carbon atom is single-bonded to both oxygen atoms; the negative charge is delocalized as lone pairs so that each oxygen maintains an octet.
Use the information provided to answer the questions below.
(a) For Diagram A, calculate the formal charge on each atom directly involved in the –COO⁻ group (both oxygens and the central carbon).
(b) Repeat the formal-charge calculations for Diagram B.
(c) Explain how the experimentally observed identical C–O bond lengths support one diagram over the other. In your explanation, discuss resonance and the distribution of negative charge.
(d) Using your preferred diagram from part (c), justify why the conjugate base of acetic acid is more stabilized than the conjugate base of ethanol, thereby accounting for the greater acidity of acetic acid.