Squaric acid is a diprotic acid with both protons more acidic than acetic acid. After losing both protons, all the C-C bonds of the ring are equal in length, and so are all the C-O bonds.
Which statement best explains these observations?

Question

Squaric acid is a diprotic acid with both protons more acidic than acetic acid. After losing both protons, all the C-C bonds of the ring are equal in length, and so are all the C-O bonds.

structure

Which statement best explains these observations?

TestHub · Accepted Answer

Removing the first proton gives an anion stabilised by resonance and intramolecular H-bonding. Removing the second gives a dianion with four equivalent resonance structures : the charge is shared by all four oxygens and every C-C and C-O bond is the average of single and double, making all of them equal in length. This strong stabilisation of both conjugate bases explains why both protons are more acidic than acetic acid.

Chemistry - GOC Question with Solution | TestHub

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