Hydrogenation reactions are a subtype of reduction reactions that add hydrogens to double and triple bonds. These differ in the types of products made and the stereochemistry of the mechanism.
The definition of hydrogenation.
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now and discuss a few reactions that add hydrogen is to triple bonds. And these were gonna be called in general hydrogenation reactions. The major difference between them is gonna be how Maney Hye Jin's, they add, and in what? Stereo chemistry. So let's go ahead and check them out. Basically, there's three major types of hydrogenation that we look at, and these were going to be reactions that turn triple bonds into either double bonds or single bonds. So basically, we're taking one type of hydrocarbon and making it a more saturated version off that hydrocarbon. Remember that the definition of saturation or degree oven saturation has to do with how maney hydrogen are on that molecule. Okay, so when all of these reactions what we're doing is we're increasing the saturation of the molecule, meaning that we're adding hydrogen to it.
Using Catalytic hydrogenation or Wilkinson’s Catalyst to turn alkynes to alkanes.
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So let's look at the first and probably simplest form of hydrogenation, and that would be what we call full saturation. What that means is that I'm taking a double bond or a triple bond, and I'm fully saturating it with hydrogen. All right, we can do this by two different re agents. We could do this with either catalytic hydrogenation. We should be these reagents right here in the first arrow. That would be basically H two over a plate, platinum, palladium or nickel catalyst. Okay, Or there's another reaction we can use as well. Called Wilkinson's catalysts and Wilkinson, Wilkinson's catalyst is usually for the same purpose. To take double bonds and triple bonds and fully saturate them toe al Keynes. Alright, so, as you can see, the Regents for Wilkinson's catalysts are a little bit confusing. It's got the H two because we're adding hydrogen, of course, but the catalyst is way different. In this case, we're gonna use rhodium with these three try fennel Foss fiends, and then a chlorine. It looks messy. Okay, I'm not gonna draw the whole thing for you as long as you can recognize that that's Wilkinson's. That's fine. Okay, so now the only thing about full saturation is that this is a little bit of a misnomer, because remember that rings also count towards on saturation. A ring is something that it's missing. Two Hydrogen is because two ends are attached to each other, and actually these reactions do nothing to rings. So what's gonna happen is that all the double bonds and troll bonds will be gone, but the rings will stay intact. Alright, One more thing before I draw these products, notice that the stereo chemistry says sin addition. Okay, Sin addition is another way to just say that we're going to get sis products. So what that means is that I would expect the hydrogen is that we're adding toe ad from the same side of the double bond or the same side of the triple bond. So let's go ahead and draw our products. Basically, I would get the same exact sigma framework when I say Sigma framework, I'm just saying all the Sigma bonds were the same, but now I would get a single bond over here so that Triple One just turned into an Al cane and I would get this alcohol still here and then I would finally get that double. Bond is also gone, meaning that there's no pi Bonds left. Okay, what this is really good at is getting rid of pi bonds. That's pretty much it. So here I did include stereo chemistry because there are no Carol centers, so I don't really have to. But if you were wondering, where did these hs come from? Especially maybe on the double bond, they could have both come from the same sides. That means, like, let's say that one of the HSE came from here and one of the H is came from here. Notice that they came from the same side of the double bond. Then that means that my alcohol be forced to go down. Okay? Alternatively, I could have also had the h is ad from the bottom, which means that the O. H would have gone up as well. Same thing with this with the trouble bond. Except that the trouble one. I added four hydrogen I didn't just add to, so I basically added, let's say, two from the front H H and I also added to from the back. So let's say H h so what I wound up getting was instead of and then also. So now that this this this carbon here makes sense as CH two. But this one looks like it doesn't make sense because it's also ch two. But remember, there was already one h to begin with on that triple bond, so that last H is still there, and it's right next to my head. So does that make sense? Basically added the two blue hydrogen, then added to green hydrogen is and then this black H was just always there. All right, So basically, you can think that full saturation or one of these two catalytic or Wilkinson's is going to completely get rid of all pi bonds, all double bonds and ultra bonds. Easy, right, cool.
Catalytic Hydrogenation or Wilkinson’s Catalyst:Alkane products
Using Dissolving Metal Reduction or Lindlar’s Catalyst to turn alkynes to alkenes.
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let's move on to the next reaction. And actually, these next two are gonna be both considered partial saturation. So what that means is that for these next two, I'm not saturating all the way to an Al cane. In fact, what I'm doing is I'm taking a triple bond and I'm Onley reacting it toe a double bond. So I am adding to hydrogen is. But I'm stopping there, okay? And the first of these, the really the biggest difference between them other than the re agents, which are totally different are the stereo chemistry. Noticed that my first one is anti addition. Notice that my second one is Sin Edition. That's gonna have a difference in what products look like. So let's look at this first one. The first one's called dissolving Metal reduction. Okay, Dissolving metal reduction is just another name for these re agents. And what it is is that we have some kind of metal lithium or sodium. Your professor can use either one in some kind of liquid amines source. Many times that, I mean, is gonna b NH three. But there's a lot of other things that could be it could be n h two, ch three or it could be just any kind of usually primary or secondary Amine. Alright, cool. So we've got that part down. What does it do? Well, we learned. I just thought you guys that partial saturation means that it's on Lee working on triple bonds. So notice that I have the same or a very similar molecule here. And what I'm wondering is, how should I draw this? I have the same Sigma framework, but for example, should I draw the double bond, or should I leave it there? I should leave it there because it turns out that since this is partial, saturation has no effect on Al Keene's. No, the fact on Al Keene's all right, it's on Lee going to work on triple bonds. So now I've got this triple bond. Is it gonna work on this one? Absolutely. Well, what does anti Edition mean? Anti edition. If you remember, that just means I have trans products. Okay, so what that means is that I would expect that my hydrogen are gonna add from different sides of this double bond. What that means is that I should actually draw the double bond in a trans position. Why? Because the two hydrogen is that I added must have added on different sides okay of different kinds of dope on which means that they were anti addition Is that making sense? So what that means is that dissolving metal reduction is important because this is a way that we can turn triple bonds into trans double bonds. That's gonna be your product. Trans double bonds. Pretty cool, right? So that's something you have to keep in mind because for synthesis later, when we start trying to make molecules, that's gonna be really the only way that we know how to turn a troubled one and make it trans cool. So now let's go to this next one, which I'm sure you guys can already kind of anticipate what's gonna happen? Notice that this one's called Lin Lars Catalyst and Lynn. Lars catalysts has a lot of different re agents that you could use. Unfortunately, different textbooks, different professors have their own way of writing it. Some professors, they're gonna be really easy. They're gonna be like, you know what f all of these re agents we're just going to write Lynn Lars. Okay. They're gonna put H two inland, Lars, and you're gonna know that That's Lynn, Lars. But some professors are gonna use the actual re agents that are in the textbook. So some textbooks have this as the P two catalyst. Okay, so the P two catalyst is one form of Lin Lars. Another form is actually with lead acetate and Quinn a lien. These are re agents that you just have to recognize that there. Lynn Lars, you don't need to know exactly what they look like or draw them or even know the mechanism. But you do need to know is recognize that these Erlynne lars thes air also just you guys know another term that you may here is that these are poisoned catalysts. Okay, now, what could hoops cat thio catalysts? Wow. Okay. Sorry, guys. Spelling isn't my forte. So poisoned catalysts. What does poisoned mean? What it means is that thes catalysts have been created in such a way that they're not going to reduce all the way or they're not gonna hydrogen eight all the way. Instead, they're going to stop at a given point, Okay? And that's why they're called poisoned. All right, so these air three different ways that you could see this re agent. Just be aware of them. Okay, Um, personally, I hope that you, professor, just writes Lynn Lars, But you may see these other two regions come up. All right, so now it's finally get into the products. What should I draw from my product? Well, what I should draw is that I should still keep that double bond. Right, Because whenever you have partial saturation, that means you're gonna have no effect on double bonds. Yeah, that means the Onley difference. The only thing that I'm really touching here is the triple one. So how should I draw it? Well, in this case, I have sin addition. And what sin addition means is that I'm gonna get cysts products. Okay, So what I would expect is that I have to draw this double bond now, in a way that has my our group cyst to whatever that double bond is. So I'm going to get out of the way here and draw this for you. I would actually want to draw my stick down this time. Why? Because if I create, like a little fence a parallel to this stole bond. What I see is that now both of my groups are gonna be on the same side of the fence. So this creates cysts, Double bonds. All right, so I know that was a lot of re agents. I'm just going to stay here for a little bits that you guys can write that down. But anyway, I know that seems like a lot of re agents, but really, it's not that bad. Especially when you're not having to consider any mechanisms at this point yet. I just want you to know the re agents recognize what they do and be able to draw them. Okay, be able to draw the products, all right? And keep in mind the stereo chemistry, because the stereo chemistry really is the most important part of these reactions. All right, so let's move on to the next topic.