With a pKa of 1.2, squaric acid is unusually acidic for a compound containing only C, H, and O. Write a Lewis dot structure for the conjugate base of squaric acid and, using curved arrows, show how the negative charge is shared by two oxygens.
So, here we have a compound called squaric acid and for a compound that only has carbons, hydrogens and oxygens, it's unusually acidic with the pKa of about 1.2. So now my question is why? well actually guys if we go ahead and deprotonate this, just go ahead and draw this here, we can share these electrons, right? this extra lone pair with another oxygen. Now, which one would that be? Well, let's go ahead and resonate to figure it out, right? So we can kick electrons from here, right? We can kick a lone pair on to this bond but now this carbon has too many bonds. So, where is it going to go? Well, it's got, it can't really kick electrons this way, right? And then we have a positive charge over here, so we need to keep our double bond here, well at least attached to this carbon, so we're going to kick electrons this way but now this carbon has too many bonds, so what do we do? we kick electrons up like that. So, our resonance structure is going to look very similar, right? in fact it will just look like the same thing but rotated, so now we've got our double bond up here, we've got our O with three lone pairs now and a negative charge, we've got our OH still here with two lone pairs, we got our oxygen here now double bonded with two lone pairs and then we've got our double bond up, right? So, in fact this just looks like we rotate it 90 degrees counterclockwise, right? But it is a resonance structure. So, just to get back to this we would kick electrons down, I'm sorry, we would kick electrons off of this bond and remove these electrons here and then back that way, right? And now we've got two resonance structures here and at any given time what we end up with is a resonance hybrid that looks kind of like this, we end up with our O here, I'm not going to draw our lone pairs here, I'm just going to say we've got one bond here, a partial double bond coming all the way through, right? And a partial bond here with our oxygen, with our OH over here and our double bond O here, okay? So, at any given. So, our resonance hybrid looks like this and it's got a massive distribution of charge, right? So that's why it's that acidic, that's why it's got a pKa of 1.2. If you have guys have any questions please feel free to ask, if not, let's move on.