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Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

14. Synthetic Techniques

Synthetic Cheatsheet

Here is an overview of the 3 synthetic techniques you need to know. Let's get to it! 


1. Alkane Halogenation 

2. Organometal Alkylation 

3. Alternating Elimination/Addition to Move Functionality 


Review of Cheatsheet

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So it turns out that I could actually boil this entire chapter down toe one page. And that's actually what I tried to do earlier this semester. I spent a lot of time just tearing apart this chapter and thinking, What's the shortest way that I could teach it? I got everything on one page was actually really impressive. So I'm gonna share that page with you now. But obviously, I'm not just gonna teach you one page. I'm gonna give you an overview right here of three of the three cents synthetic techniques that you need to know. Okay for this chapter, and then we're gonna practice it a whole lot. I'm gonna give you guys lots of practice problems and lots of application. Okay, so let's go ahead and get started. I'm gonna teach you as the three important rules for synthesis that you need to know. The first rule s I'm calling this the synthetic cheat sheet. Like I said, you use this as your reference point for the whole chapter. Okay, So the first thing is Al Cane halogen nation. A lot of you guys already know this, but al canes are un reactive, so if I want a functional group on an Al cane. I'm gonna need toe halogen. Ate it first. Do you remember what we used to Allegheny Al Canes? Radical reactions, Right. So I could use something like B R two over heat. Okay, that would be an example of selectively halogen eating in al cane so that I can then functional eyes it later. So that's already functional. This is, But check it out. I could now do a bunch of stuff to it. I could substitute for that. I could do like an s and two I could eliminate. I could make do in addition reaction. Now, this is kind of like I just do it like this because it kind of looks pretty, But this is kind of like not true. What you would do first is you would actually eliminate first, and then you would add right, because addition, reactions happen to double bonds. Okay, so, whatever. But I'm just saying that forming that first halogen is always gonna be the first step. Anytime you start off with a simple all cane. So you're starting off with just cycle panting, You know, whatever you need, you're gonna need to hallucinate first. All right, so that's the first rule. Easy, right. Cool. Let's go into the second rule. The second rule is called Organa Metal Calculation. Now, two important words. What is organa Metal. And what is calculation? Will Organa Metal just stands for any is just any molecule that is part carbon and then part some metal. And they're they're they're bonded together. Okay, So an example that that you're very familiar with is a sodium Alka night. Okay. A sodium alcon. I'd would be an organo metal because I have a carbon with a negative charge. Right? And then I have a sodium with a positive charge. See how they in this case, I didn't draw them bonded together but their associate with each other. So that's an example of an organo metal. Cool. Well, there's other types of organo medals tool to There's also this one right here that you don't know very well, but that's a green eared. Later on, we're gonna use that. Okay, But for right now, just keep in mind that both of these count as organo medals and organo metals are very strong nuclear files because they create negative charges on carbon. Okay, what? Turns out that if you're ever trying to do a synthesis and you're trying to add carbons to a chain, let's say you start off with a four carbon chain and you need a five carbon chain, okay? Or you need a 10 carbon chain. What we're gonna do the Onley way that we can add carbon carbon bonds in organic chemistry. One is through organa metal calculation. That means reacting these with something that's going to add alcohol groups with an electro file. So what Electra Falls do we have? Well, we have to comment, Electra falls, but one of them, we're gonna use a whole lot more in this chapter, and that's alcohol. Hey, leads. Okay, because remember that alcohol hey, leads do the opposite. Instead of putting a negative on the carbon, they put a partial positive on the carbon. So that's perfect, cause then what that means is the negative for one, carbon is going to be attracted to the positive from another carbon, and they're gonna link up. And that's what we call a calculation. Alright, pretty easy. It's just whatever that alcohol group is, it gets added on the X leaves a leaving group. It turns out that a carbon Neil is also very common Electra file because as a strong die pull pulling away from that carbon. So it also places a very strong partial positive on this carbon. Now, we're not going to deal with this one a whole lot in this chapter. But I still want you guys to hold on to this and realize that there's more than one nuclear fathers more than one electrical. All of these things is the This is the big Four. The's Big Four are really important when it comes to making carbon carbon bonds. Alright, the ones we're gonna deal with mostly today are the sodium Alcon eyes and the alcohol highlights Alright, which you already should have experienced with. So that wasn't so bad, right? That's another very important rule. Any time you're adding carbon, think sodium Alcon, I think organa metal. All right, so then what's the last thing? The last thing is probably the most useful of the three, okay. And what it is is that moving functionality? Okay, there are many, many times in organic chemistry that I have ah functional group in one place and I'm trying to get a functional group in a different place. I'm trying to go from one place to another. It doesn't even have to be the same group. It could be an alcohol here, and it could be a sulfur over here, whatever. The main point is that if you're trying to move one function from one place to another, then there's really there's really only one way to do that. And that's by doing alternating elimination and addition reactions. Okay, so elimination, in addition, as you guys know are opposites of each other. Okay, so they're opposites. Since they're opposites, that means that they can kind of undo each other's effects. Okay, so basically, what we do is we, we add, I mean, we eliminate to make a double bond, and that double bond will link two carbons together, and then we add to the carbon that we want to go in that direction on. Then we do it again. Then we add to that carbon. Then we eliminate. Then we can do it again. And by doing successive elimination, addition, elimination addition, you can wind up moving the functional group from one part of the molecule to the other, and we're gonna do a lot of this today, but I just want to let you guys know that's really the only way to move functional groups. If you want to take a function from the right side and make it to the left side, you have to do alternating elimination edition. Okay, well, it turns out that any time you're eliminating and any time you're adding you actually have a choice of which direction to go in because now you guys know how to do eliminations towards more substituted and less substituted. And you also know how to do additions towards more substituted and less substituted. The thing is, they have different rules. They have different names. So remember that if you're eliminating and it's towards the more substituted location that was called Zaitsev Okay, well, remember when you're adding and you're adding towards the more substituted, that's called Markov Nankov. Okay, that's really important that you link those two together because both of those the sites elimination along with the market knockoff addition are always going to go towards or move towards my more substituted locations. Okay, so what that means is that if I can use re agents that are going to do sites of eliminations and Mark Avnet competitions. I'm gonna progressively move more towards the center of my molecule. The thing that's the most substituted does that make sense? Whereas I have opposites of that I have from if I want to go towards the less substituted elimination I would do. Ah, Hoffman, right. That's the less substituted. And if I want to move away from the center of the molecule to the less substituted edition, I would say it would be an anti more common in competition. Does that make sense? So both of these you put together because both of these were going to favor the less substituted direction. Okay. And these were gonna favor the outside of the molecule, so I'm just gonna put here the outside of the molecule, and this is gonna favor the center of the molecule. Does that make sense? So what's so cool about this? Is that now it's almost like I've given you guys to roads and you can choose which road to take based on what you're given. If you know you have to move. If you have a substitute, that's all the way at the edge of the molecule, and you need to move it towards the center. Then we're going to start using a combination of addition and elimination of more called Nicole of incisive. Obviously, the opposite would be true if we're trying to move towards the edges. Okay. Well, now all we need to do is just need to figure out what are the actual re agents that we can use to do this. Okay. And let's start off with the eliminations first, because those are the easy ones. Okay, If I want to just do a sites of elimination, what kind of re agents favor as sites of elimination? Do you guys remember? Okay, so in general, I'm just gonna put here a small, strong base. Okay, Small, strong bases, favors, site sieve, and really just examples you can think of your own. But why do you guys just start yelling out some examples of small, strong bases? Yeah, I think that you got that one. Um, it would be like for example, n a N H. Two is an example of a strong small base. Okay, Also, n a h. Okay. Also on any of the oxides. Okay, so any Oh, are negative Would be a small, strong base. Of course not if you make the our group too big. But if you keep it small, that would be a small, strong base. Alright, um, and we can keep thinking of a few more. Um Well, even ALCA nights. Okay. Alcon eyes are small, strong bases in the right situations. They can favor that as well. Okay, so these are all examples of bases that favor the Hoffman. I mean, that favor the site sieve elimination. So they're gonna make the double bonds go towards the center of the molecule or towards the more substituted location. Okay. Now, if I wanted to ah, Hoffman elimination instead. Then what kind of regions would I use? I would use my bulky bases, right? Remember, there were just a few bulky bases that you needed to know. And I told you guys like l d a TV talk side and l I t m p thes air. The really common ones. Okay, that you just need to be aware of. If it's not one of these, then you can pretty much assume that it's not bulky. Okay, cool. So now you guys. You guys already knew this. But now this is just helping you guys to solidify. Okay, if I wanna go, I wanna eliminate in the more subdued direction I do sites it less attitude. I do Hoffman now for additions. It turns out that addition is a lot more varied because elimination you just make a dope on. That's it. But for addition, you can either add alcohols or you can add Al Kyohei Lloyd's. Obviously there's other things we could do to, but these are gonna be the two most common categories because a lot of times either an al Kyohei lied can be substituted for anything. You could do an s and two on it. And in alcohol tends to be a very common re agent that we like to add to stuff. So it's just important to know the alcohol re agents. Okay, so let's go ahead and write down these reactions. What if I'm trying to do a Mark Kafelnikov edition of alcohol? So now this. Is that the point where I'm starting with a double bond? I'm trying to do a Markov knockoff edition of alcohol. What regents could we use for that is gonna help you categorize all the regents. Okay, well, the Regents we could use would be first of all, the easiest one would be just acid catalyzed hydration, right? H two s 04 over H 20 okay. Or any h a Any strong acid. So we know that that would work. Are there any other regions that make a mark Cognitive edition of alcohol? Oxy Merck. Okay, this is gonna be a little bigger, but it's H g o A. C two, um, with water and then over N a p h four and O H minus. Cool. So those are your two choices? I'm just going to kind of make a line there. So you guys know that those are two different things, but those are our possibilities for more cognitive addition. Why would I choose one over the other? Do you guys remember what's better about one or why? I don't know. What's the situation that I would want to choose? Let's say acid catalyzed hydration. Why would I want to choose that? If I want a shift? If I want a car broke out and shift, you can even right here Positive to just remember that would shift, whereas Oxy Mark would never shift. So if you want to shift, that's not a good choice. Okay, Cool. So how could I do, um, our cognitive addition of an alcohol? Hey, lied instead. This is really easy. Think about it, Markov. Niqab. Alcohol highlight. I'm adding to a double bond. Just a checks. Okay. H X is always gonna do your Mark Avnet composition of a halogen, and it will rearrange. And there's no equivalent of Oxy Merc for h X. There's no HX that won't rearrange, so just got to deal with it. Okay, so that's if I'm trying to add substitue ints towards the more center of the molecule. But what if I'm trying to go towards the outside with my addition? Reactions from trying to add an anti market niqab alcohol or an anti Markell Markell Makov halogen. Well, in that case, we would use a completely different re agents, so we would use here for alcohol. Do you remember a way to make anti more common? Cause alcohol? Yes, you do. Because remember, it's my favorite reaction. So it would be hydro beret shin. It would be B H three th f over H 202 and any O. H. Okay, So hydro beret shin is the way that we would add an ante Markov Niqab alcohol. Okay. What's the way that we wanted if we wanted to make an ante Markov Nankov halogen instead, not alcohol. Halogen. Well, then we could use a radical reaction because remember that H X is gonna go more comic. Aww, unless we add peroxide. Okay, If we add peroxide, then that makes it Ante Markov knockoff instead. Now, maybe you're maybe it's making sense to you. Why I kept emphasizing guys remember hydro operation and remember radical Hydrology Nation because I kept saying this is gonna be very important for synthesis. Why these air the Onley Two reactions in Orgel one that go ante Markovic office. These are gonna be the Onley two edition methods that you have to go outside towards the peripheral. Okay, towards the edges of the molecule. That's why it's really important. Okay, So what's so cool about this chart? Is that yeah. Ah bunch of reagents aren't here, Okay, I totally get that. But the important reagents for moving functional groups are here now. So what that means is that now, as we're moving functions from one place to another, we could just use this as a cheat sheet and say, Which direction do we need to go? Is it is it more subdued or less on? Then you figure out what to do now also, you might be wondering. OK, Johnny, how do I know when toe add, how do I know when to eliminate? Okay. It's just whatever you're starting with. So if you start off with a double bond, let's say the question is turning this double bond into this functional group. Oh, on the other side of the molecule. Well, then, if you start with, it's all about your first step. Always has to be in addition. Okay, So that means you would look towards the addition section, you'd say. Okay. Is this gonna be a more substituted direction or less? That's the one you pick. Okay, then. Opposites true. If you start off with an alcohol hey, lied or alcohol, then you need to start moving it somehow. So you need to eliminate first. And then once again, you would look at your chart and say, Okay. Is it gonna be eliminating in the more substituted or the less substituted. It's really awesome how it really turns into like a formula. Once you have this in your mind, you start to think, Oh, what can I do? What do I need to do instead of it just being a guessing game Now you actually have a blueprint for what to do. Okay, so that was a really big intro of this sheet. Like I said, this basically summarizes the whole chapter. Now we're going to do cause you're gonna do a lot of practice and I'm gonna individually focus on each of these sections. Alright. So I hope that made sense, Let me know. But also, just wait it out a little bit in case you're confused, because I'm going to go into depth on all three of these things. We're gonna do a lot of examples. All right, so let's go ahead and move on.