This is the first of three ways to add alcohol to a double bond. It is similar to hydrohalogenation in terms of mechanism, however it will require a protonation and deprotonation step since it is acid-catalyzed.
1
concept
General properties of acid-catalyzed hydration.
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guys. Now we're going to discuss what might be the most important addition reaction of this entire section, and that's called acid catalyzed hydration. Keep in mind that of the three methods to make alcohol that we're gonna learn in this section, acid catalyzed hydration is considered the first off three ways to make alcohol's by addition. So let's go ahead and get started. So, guys, as a catalyst, hydration is more similar than it is different to the addition reactions that we've learned so far. The intermediate is the same as the ones that you've seen so far, which is that it is a Carvel cat ion. Okay, now, if the intermediate is a carpool Catalan, what do you think that says about its ability to do shifts or rearrangements? Totally. This thing is going to rearrange all the time. Okay, Now, that could actually be a bad thing, because remember that rearrangements lead toa unpredictable outcomes for our reactions. It could lead to a reaction or product that we weren't expecting. So we may actually see that the ability to rearrange is a drawback that we have toe fixed later on, but we'll get there later. Okay, Now one thing about carbo Canadians and their stereo chemistry is that they're very unpredictable. Carbo Catalans Remember the tribunal plainer so they could be attacked either from the front or from the back? Okay. And what that means is that the stereo chemistry of our products is really still gonna be unknown unknown because we don't know where it's hitting. There may be several Cairo centers produced, so I don't want to say anything more than just unknown thes. There's usually ah, big mixture of Cairo products in these reactions. Okay. And as we said earlier, ask allies, hydration or simply known as hydration is the first of three methods to make what alcohol. So we know what my product is gonna be an alcohol. Okay, Now, is this gonna be a Mark Koebnick off alcohol or an anti Markov nick off alcohol? Well, it turns out that in the section we're gonna learn how to do both. We're gonna learn how to do Mark and anti Mark alcohol's, But hydration is definitely a Mark Cobb Makov reaction. It's a mark of nick off alcohol because you're Carvel. Catalan is always gonna want to form in its most stable location. Okay, So before we go to the general reaction, let's just read off a few bullet points because they will be helpful for us. Okay, Now, notice that are re agents are H 20 in H two s 04 Okay, now, put more. Generally, that's the most likely way to see it. But it's simply gonna be h 20 with some form of acid or h a recall that when I talked about dehydration, I said dehydration was h 20 and H A. So, actually, the Rea agents haven't changed it all since dehydration. They're the same. So you might be wondering, Johnny. Well, how can I tell if the regents are exactly the same? How can I tell if it's gonna be in hydration or a dehydration? How? How do you know? Well, you look at what you're starting with, since you're starting with a double bond. That means that a double bond is going toe hydrate toe on alcohol. So it's the same re agents as acid catalyzed dehydration, except with a starting with a double bond instead of starting with an alcohol. All right, cool. So you look not at the re agents But you look at the starting the starting molecule to know if you're going to go into hydration or dehydration. Just think about hydration. Means you're adding water and look what we just did. We're adding a water. We're gonna add an H, and we're gonna add a Ohh. That means we're hydrating the double bond. We're adding a water to it. Okay. Now, in terms of the general mechanism, it's also gonna be very predictable. It's going to be the same as Hydra College Nation, which you guys might remember is just the simple reaction of a double bond with H X, which is really our example. Reaction for addition. Okay, so it's the same general mechanism. Is that except that we're gonna use water as the nuclear file. So instead of using X minus and attacking X minus, we're gonna tap water instead. Okay. And then, guys, remember I stated this when we talked about other like dehydration. But remember that every acid catalyzed mechanism always is very predictable. It always starts with something, and it always ends with something. If the name is acid catalyzed, that means it be always begins with Protein nation, and it ends with deep protein nation mhm. Okay. That's because if it's acid catalyzed, it means you're always gonna put a proton on something. And at the end, since it's a catalyst, you have to take that proton off so you could regenerate your acid. Okay, so just look at the general reaction here. The general reaction states that a double bond with water and acid is gonna do what? Well, notice that this is Mike Markov, Nankov sites. And this is what I would call my Auntie Mark Kalashnikov sites. This is my mark site. So even without knowing the mechanism, because I told you guys all the things about the properties of the reaction, I can predict that my product is gonna look like what? I'm gonna have a Markov nick off alcohol and alcohol in the most substituted place. And then the h of the water will be in the least substitute place. So I'm adding water. I'm adding h 20 but the O. H forms mark and the H forms on the other position. Okay. Now, the last thing you might be wondering, John not wondering about me is wondering, um, what's up with squiggly line? Because it looks super weird, right? You may have not seen that before. He might for gotten what that was. Just remember, guys, if you see a squiggly line that means of the like that it means that it's unknown stereo chemistry. It means that it could be towards the front. It could be towards the back. You're not expected to draw all the stereo I summers because that could be a huge burden. All you need to know is that that h went somewhere okay on. That's why I put the stereo chemistry unknown. Because you're not there could be up to four different stereo customers on these things. So I don't think you're expected to draw all of them just to know that several could form. Okay, awesome guys. So that's it for this. So then let's move on to the next problem where we're gonna draw the mechanism at length
This reaction uses the same reagents as acid-catalyzed dehydration, so how do you know which reaction to use? Just look at what you are starting with:
General Reaction:
Note: The squiggly line on the product just means “indeterminate stereochemistry”. We aren’t sure where that –H will add, so we’ll just draw it on a squiggly line.
2
example
Acid-catalyzed hydration mechanism
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So what I want to do for this question is I just want to show you guys the full mechanism. Okay? I'm gonna draw the full mechanism stuck by step, and it was just gonna follow me as we go along. All right? So in my first step, I've got my double bond, and my double bond is a nuclear file. I'm looking for an electric file. Something that I can grab it in age from. Okay. And that's gonna be my sulfuric acid. So I go over here, okay? And now notice that I drew the sulfuric acid a little bit weird. Okay, this actually just has to do with the fact that the way that sulfuric acid is drawn right here, it's very difficult to take a proton off of it. While it still makes sense, chemically, it's better if you draw it in this notation. So you can actually see where is the age attached to? Oh, it's attached 10 it's not attached to a s. Okay, so I know this is a little bit tricky, but I am gonna ask you guys to memorize how to draw sulfuric acid when you're trying to de protein ate it. Okay, I know it sucks, but this is gonna make your life easier when it comes to actually drawing the product. Okay, so here we go. We've got our double bond and I'm looking for my electric file. That's gonna be this age, Okay? Because my h is acidic. So I take my double bond, I grab an h, give the electrons to the Oh, what I wind up getting is a caramel Catalan right here. Cool. Alright, so I've got my car broke a tie in. What's the next step? I've got that. Plus, I've also got o s +03 h Negative. Okay, So is that going to attack? Well, not yet. Okay. Because on top of that, this carbon carbon is not very stable. Secondary. And if it moves over, it could become tertiary. So what we're gonna do here is a shift. What kind of shift would it be? Well, in this case, this is a metal group. I only have metal group surrounding this carbon. So what that means is that I can't do Ah, hide, right shift. Remember that hydrate ships are always gonna be preferred, but I don't have any method I don't have any hydrate hydrogen on that carbon. So that means I'm forced to do a metal shift. So I'm gonna grab any of these methods. It doesn't matter which one, and I'm gonna move it over to this Carbon. What this is going to give me is a constitutional isom er at the end. That looks like this one, too. Ch three shift. And now what I'm going to get is a new carbon caddy that looks like this. We're now my positive charges down there. Okay? Why is that? Because I used to have four bonds right there, and now we only have three. Okay, so I've got my Carvel Catalan, and now we're faced with the dilemma. What a text. The Carvel Catalan. Okay. And I basically got two different nuclear files. I've got the anti on from my acid, and I've also got water. Okay, One of these nuclear files is negatively charged, and then one of them is neutral. So which of these do you think is the stronger nuclear file? Okay, it's usually gonna be the negative charge. So I would say that actually, the conjugate base of my acid. Okay. The Oso three each net O s 03 h negative would be the stronger nuclear following. I would expect it to attack, but we've got another variable in the mix. Okay, This is actually gonna be a repeating theme throughout this section. It turns out that even though the OS 03 h negative is the stronger nuclear, Valka is negatively charged. There's just gonna be a whole lot more water. So imagine that I've got one of these guys because I just donated the acid, whatever. And then I've got, like, a billion of these guys. Okay, imagine that I've got a billion water molecules, and I've got only one of the Oso three h negative. Even though the sulfuric acid an ion is gonna be Even though it's gonna be a stronger nuclear file, there's not a whole lot of it to go around. So what that means is that this carbon Kati and is very easy to attack. It's very easy for water to attack us. Well, so it's just gonna attack with the first thing that collides with it. And because of the way that I have this solution mixed up, I'm always gonna have way more water, Then I am gonna have an eye on. So what that means is that even the water is weaker. It's going to be the one that attacks. Okay? And that all has to do with the ratio of water. I have tow acid. And just so you know, for a hydration that's usually going to be a lot of water. And on Lee, a little bit of acid just to catalyze the reaction. Okay, so I hope that makes sense why the water attacks and why the Seoul fate doesn't. Okay, so now what we're gonna do is we're gonna draw the final or not the final. But the new product, which is that I haven't Oh, each h positive. Okay, because the O still has those two. H is on it now that has a formal charge because it doesn't wanna have three bonds. So can I just tell you that the last step is going to be in this reaction? The last step is always going to be in any acid catalyzed mechanism. It's always gonna be deep Throat Nation. Okay, So what that means is that the last step I need to take away a proton from something and regenerate the catalytic acid. Okay. And what's that going to be? Well, the catalytic acid in this case was the O S 03 h. Negative. Okay, so in this final step, what I could do is I could take that negative charge, and I congrats that age and deep protein ate it. And finally get my product. My product is going to be in alcohol. Okay. Plus, it's gonna be my sulfuric acid. All right, So notice that. What do we do? We went ahead. We took a double, wanted the beginning, were acted with Agnes Acid when we wound up getting was an alcoholic the end of our cosmic off alcohol that shifted so can rearrange. And we got our acid back at the end. Notice that we started off with a choice of four and we ended up with a choice of four. That means that it was a catalyst. Okay, because we got the same amount of acid at the end as we have the beginning. All right, this very common reaction in this section. I hope you guys understood this mechanism. It's really important that you guys practice it, though. Okay? So let's go ahead and move onto the next topic.