A carboxylic acid has two oxygen atoms, each with two nonbonding ...

Question

A carboxylic acid has two oxygen atoms, each with two nonbonding pairs of electrons.

(a) Draw the resonance forms of a carboxylic acid that is protonated on the hydroxy oxygen atom.
(b) Compare the resonance forms with those given previously for an acid protonated on the carbonyl oxygen atom.
(c) Explain why the carbonyl oxygen atom of a carboxylic acid is more basic than the hydroxy oxygen.

Accepted Answer

Hey everyone, let's solve this problem. It says an ester has two oxygen atoms each with two non bonding pairs of electrons draw and compare the resonance forms of the can ions produced when protein nation occurs at a the ALC oxy oxygen and be the carbon oxygen, suggest which of the two oxygen atoms is more basic. And give a suitable reason for your answer. So the problem is talking about an ester. So let's review what that looks like. We have an R group bonded to a carbon which is double bonded to an oxygen and single bonded to another oxygen that has another R group attached to it. And like the problem says each oxygen has two lone pairs or non bonding pairs of electrons. And we want to see the residents forms when either oxygen is protein ated. Right? So the cast iron produced when proto nation occurs at either oxygen. What does that mean? Pro nation? We're just adding a proton. Right, adding an H plus so which oxygen is which? Well, I definitely know carbon eel oxygen is the one that is double bonded to the carbon. Right? My carbonell group And the elk oxy oxygen must be this one. Okay, suggest which of the two oxygen atoms is more basic. Okay, so how do we determine that? Well, in order for a reaction to be favorable, it should be more stable. Right, reactions favor stability. So that means we want to know which cat eye on is more stable when it's protein ated. So that's why the question is asking about resonance structures right? Because we know that resonance can create stability. So, knowing that if a structure has more, sorry, if a compound has more resonance structures then it will be more stable. Right? Because that charge can be de localized around the neighboring atoms. Okay, So let's draw out what each resonance structure would look like if each oxygen was rotated. So, first we have Alcock see oxygen. So this part stays the same. And we have our proton, our acid over here. Right. And it says for the ALC oxy oxygen, these lone pair electrons are going to be pro donated from that hydrogen giving us that's oxygen. And there will be two lone pairs still left on that oxygen giving us a plus one formal charge on the oxygen. Right? There's +12345 electrons touching it. It likes to have six. Are there any other resonance forms that could be possible for this compound? This structure rather? No. Right. This charge is too far away from that lone pair. So this has no resonance stabilization. Okay, what about the other oxygen? We have our original structure. It takes a proton this time from the carbonell oxygen which gives us Yes. So our oxygen will have the proton. It will still have one lone pair. Right, This side doesn't change. And oxygen has 12345 electrons touching it. So it likes to have six, giving it a plus one charge. Do we have any resonance forms here? Yes. So the electrons from the we have the pi bond next to the charge. Right so the electrons from the pi bond can swing up towards that positive oxygen. Right, oxygen is wanting more electrons because it has that plus plus one formal charge. So the electrons from that double bond will swing up giving us let's give myself more room here. Oh no. So now that oxygen will have to lump pairs and be satisfied. But now carbon only has 3-σ bonds. So it will have a plus one formal charge. Can we go any further here? Yeah, I have that plus charge right next to this lone pair here. So that lone pair is going to want to donate towards that positive carbon like this giving us. So now our double bond has moved over here, we still have a lone pair on that oxygen. Now carbon is satisfied. But this oxygen has 12345 electrons touching it, giving it a plus one formal charge. And that is all the resonance structures we can have for this compound. So we have three resonance structures here. And the first protein eating the first oxygen gave us no resonance stabilization. So which one do you think is going to be more stable protein eating the carbonell oxygen? Right, Part b So because that one is more stable, more stable cat ion will be more basic. Right, And that's the carbon Neil oxygen. Okay, I hope that made sense. That's it for this problem, and thanks for watching.

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