Currently studying high school organic reaction mechanisms and encountered a question. It goes like this:
The C=O bond and the C–O bond of an ethanoate ion is equal at 127 pm, while the C=O bond of ethanoic acid is shorter at 121 pm than its C–O bond, which has a length of 141 pm. By drawing resonance structures, explain why this is so.
So I know why the C=O and C–O bonds in the ethanoate ion is equal because both of its resonance structures have the same significance, but I'm not so sure about the difference in the bond lengths in ethanoic acid. When I tried to draw the resonance structure for ethanoic acid, I was thinking that the O atom of the hydroxyl group is sp^3 hybridised (since each of the two lone pairs will occupy two separate sp^3 hybridised orbitals), so that means there is no resonance effect.
After scouring through the internet, the O atom of the OH group is sp^2 instead. Why is this so?
(p.s. high school student here, so I might not be able to understand high-level explanations just yet, sorry)
