Generally speaking, aromatic molecules are not acidic at all, but the concept of air Mississippi can cause certain molecules to become acidic. So let's go ahead and explore how that happens. So as I said, aromatic compounds are not naturally acidic. The PKK of benzene, which is kind of your most common aromatic molecule, is if you guys remember 44. Is that a good P K? Is that a good acid? No, it's actually one of the worst assets possible. Okay, so it's obviously not gonna be a great Proton donor. Okay, But what we do find is that if a hydrocarbon can become aromatic by giving away a proton basically being an acid, right, donating a proton if that makes it become aromatic because it's becoming a college get base, then it's gonna be uniquely acidic. So our really you know are stereotypical example Here is cyclo Penta dying cycle Penta dying is ah hydrocarbon. You would expect it tohave PKK's of 44 something around there. But it's got these two hydrogen is up here now. What's special with these hydrogen is well, this is right now, not ah, fully conjugated molecule. This is what we would consider non aromatic. Correct? Because it fails. One of Hucles rule Criterias. It fails one of the four tests because it's not fully conjugated. But check this out. What if a base were to come along and pull off a proton? What kind of charged with that carbon? Now get well, make a bond break a bond. I would wind up getting a new compound that looks like this Double bond. Double bond. Negative charge. What can you tell me about that molecule? What's the air? Metis city of that molecule. Guys, this is aromatic. We learned about the four tests we learned about Hucles rule. This would be an aromatic molecule. Okay, now the definition of a good acid is that after donating a proton, it becomes a stable conjugate base. Would you say that this conjugated bases pretty stable? Hell, yeah. It's aromatic. Aromatic molecules are effing awesome at being stable. That's what they do the best. Okay, so it turns out that you guys might have not memorized this. Maybe you've never heard this before, but it's okay. Cyclo Penta dying is actually one of the most acidic hydrocarbons there is. These hydrogen is at the top have a peek? A. Of 15. Isn't that a huge difference? That means that cycle Penta dying is even more Citic than water and alcohol. Okay, it's a better proton donor than even those because it could become aromatic after donates that proton makes sense so far. Now the opposite idea can apply for molecules that become anti aromatic when donating proton. So let's look at this molecule. If a hydrocarbon becomes anti aromatic after joining a protein Thanh, then it's uniquely non acidic. So Cycle have trying. Same thing. We don't expect it to be very acidic. But what if a base were to come along and pull off this proton? What kind of charge would it now receive? So, guys, it would become negatively charged right? So I would have dull Wanda Wanda Laban Negative charge. The original molecule was what non aromatic, just like my previous example, because it's not fully conjugated. But afterwards, what's the electricity of this molecule? Guys, this one is forced to become anti aromatic, which sucks. Okay, this is like the worst acid base reaction ever. It's saying, Why did I do this? Okay, so if you can imagine the peak a of a normal S P three hybrid. I C h Bond. Right is the Pekka is usually 50. Okay, it's one of the worst assets known to man. What do you think the peak a of this specific molecule will be? Do you think it will be greater than 50 or less than guys? Because the fact that this is making an anti aromatic molecule not just a normal, you know, a carbon ion carbon ions already suck. But it's not only a carbon in it's an anti aromatic carbon ion. You can't get a worst conjugate base than this. This is the conjugate base from hell. Okay, So instead of being a PK of 50 this is gonna be a PK of 60 to 70. It's gonna be very, very high. Remember, this is on a log scale, so this is like, impossibly difficult to remove that proton because that proton would make it anti aromatic, removing that proton So as you can see, aromatic molecules are not great assets or basis. But the concept of air Metis City can be what is behind the motivating factor behind some really common assets like cyclo pence a dying. Okay, So we're gonna do some examples. I want you to read through them first, try to answer them, and then I'll go ahead and explain them for you. Okay, so start on the first one.
Determining hydrocarbon acitidy
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What do you guys think about this acid? Would it be especially good? Would it be especially bad? Okay, so in order to answer this question, we have to draw the con to get based. We have to see what would it look like after donates a proton? So we could just use the letter B and a negative charge to stand for base after it extracts this proton. What does this molecule look like? The conjugate base now looks like this. Okay, so what's the stability of that molecule, guys, this would be anti aromatic, right? So the answer here would be that I mean, this is, I guess, a free response Answer. So it's gonna be s a style. You do not have to write these exact words. I'm just kind of paraphrasing this idea, which is that this molecule would be unique. We non acidic do to in anti aromatic. Can you get base? Okay, that's it. Just explaining ourselves how this is not a good asset's actually going to be a terrible asset. Okay, so now here's another one. This one requires a little more thinking a little more thought. Would the falling to hydrocarbons be expected to have similar city facilities. Explain your reasoning. Okay, So go for that one, and then I'll answer it.
Comparing hydrocarbon acidity
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alright guys. So the only way to solve this is just to draw the conjugate basis of both and see what they look like. So at this point, we've done this a few times. I'm just going to draw the negative charge because we know that after you donate a proton, you get an electron pair so you would get a negative charge here. Hope that's fair. And then notice that on this molecule we actually have two different sites that air not fully conjugated, so it could actually have come. The negative charge could be on the top or on the bottom. Either one you choose is fine. But no matter what, that's where you would want to draw the negative charge to compare the sites. Now What I would ask is are the stability ease of these molecules similar at this point? What do you think the stability of the first one could be categorized as, Let's say, this is molecule A. It's what kind of molecule it's aromatic and then molecule B is what kind of molecule What do you think? Is it also aromatic? No, Guys, this can't be aromatic because one of the carbons is still SP three hybridized with two hydrogen with four bonds for Sigma bonds. So this is still gonna be non aromatic. Okay. So even though that negative charge might have helped with Hucles rule, we're still missing. Ah, fully conjugated ring. So this is still non aromatic. So the answer is No. No, right. They would not be expected. Type similar facilities. No molecule. A is more acidic do to having and aromatic conjugate base. Okay, I don't have to mention the conjugate based for molecule B because it's assumed that it's not gonna be aromatic molecule A is. I'll take myself. I was screaming for a second molecule. A is the one that has an aromatic conjugate base molecule. B doesn't have that, so it must not be a stable. Okay, so anyway, guys, I hope that helps to clarify the role of air Metis City in acidity. So let's move onto the next topic