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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.

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18. Reactions of Aromatics:EAS and Beyond

EAS:Retrosynthesis

So it turns out, you may be asked to propose an aromatic synthesis starting only from benzene or other benzene derivatives. We will use our previous knowledge of sequence groups to plan synthetic steps in the correct order

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concept

Aromatic synthesis starting with benzene/benzene derivatives

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Alright, guys. Now we're gonna get some practice with proposing aromatic synthesis. So at some point in your coursework, you're gonna be asked to propose an aromatic synthesis starting on Lee from benzene or other bending derivatives, and you're gonna have to turn that benzine into something more complicated. Now, in order to make this work, you're gonna have to use your knowledge of sequence groups so that you can add the groups in the right positions. Okay, It's never gonna be that easy that you don't need to use sequence groups. So let's do this first example kind of as a worked example where I'm going to give you some hints and the second one, you'll be completely on your own. So for this first one, it says synthesized the target molecule from aceto phenomenon and any other re agents. In this case, a seed often on is given to you is the molecule. But you should be aware of what the name Macedo phenomena means from naming from the naming benzene area of our clash videos. Okay, So what's going on here? What are the different transformations that are taking place? Well, one thing that's happening is that I have a key tone that at some point needs to become a Benz OIC acid. So it's interesting. I've also gotta add a nitro group in the pair of position. So it's p Paris substitution. So there's kind of a lot going on here. I've got a few different things. So one thing that I know for sure is that to turn to put a nitro into the para position. At some point, my key tone is gonna have to become What, an Ortho Parra director right now, What type of director is it? Meta, Right? Right now, this is a meta director. So if I were to nitrate this key tone right now or this Aceto Phanom, I would actually get a nitro here. Is that right? No. I'm gonna have to use my knowledge of sequence groups to figure out How can I turn that into an Ortho Parra director? Now, Ben's OIC acid? Is this an Ortho Parra director? No, this is also a meta director. So that means that I have to turn this into a Benzo kassid sometime after I've added the Nitro Group. Because if I just turn it straight into Ben's OIC acid. Then I'm going to get a meta natural group again. So there's already kind of outlining all the things we need to do. So I'm gonna let you guys get creative. This is the part that I can't do for you. You just have to get creative with all the reactions we've learned and see if you can figure out the right sequence of re agents to make this final product. So go ahead and try your best, and then I'll answer for you.
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example

Synthesize the target molecule

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All right, So this was a three step reaction. So if you got three steps, you're on the right track. The first step would be to turn this key tone into an Ortho pair director, and we learned that we could do that through Clements and reduction. So my first regent would be a zinc mercury amalgam. Okay. And what that's going to give me is an alcohol benzene. So I'm gonna wind up getting specifically ethyl benzine. Okay, Now, this is an Ortho pair a director. So since it's a north of Para director now, I can use a night Trish in to put a nitro group in the pair of position, So I'm gonna use h n and h two s 04 and that's going to give me my active electric file, which is gonna attack the pair of position predominantly, and I'm gonna get a natural group. Okay. Why did I have to do nutrition next? Because now I have a north appeared director. Okay? Now, do I have a one step way to turn this molecule into a Benz OIC acid? Yeah, I do. Guys, I can use communal four. I can use another sequence group, which is using camera Ford oxidize the Ethel. Okay, now remember that there's quite a few re agents you have to write down. So there's Cam in all four, which I mean, some professors will be absolutely fine with that. But we have to be cautious. Okay, so the rial, the right way to write it would be Canada four in the presence of base and heat. And then I guess I said three really three steps it could technically before. But with the way you could draw it is you could also read like three A and three B. Since it's still the same reaction, right? So three b would be your asset age through plus, and what that's gonna do is it's going to create Ben's OIC acid, and that's her final product. It does nothing to the natural group, so our final product ends up being this. If we had to name it right, it would be P nitro benzoate acid, right? So, guys, I hope that was a good little introduction to sequence Groups notice that there's no other order of re agents that would have worked. I had to use those regions and specifically those orders, because those were the specific sequence groups that I needed. Awesome guys. So now you have another question. Go ahead and read it for yourself. Try your hardest and then I'll come in and I'll solve it for you.
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example

Synthesize the target molecule

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Alright, guys, there was a lot going on in this question. Notice that pretty much the only thing that stayed the same was the Ethel Group. But a lot of other stuff changed. First of all, I'm gonna need to find a way to put a methyl group in the pair of position. This is Paris substitution even harder than that. I'm gonna have to put an Angeline in the Ortho position. So Ortho substitution. Okay, now I've got a few issues here. First of all, is Ortho substitution very favored in most cases? No. So the only way that I'm gonna get ah high yield of the Ortho position is to make sure that this metal group is their first or something is there blocking the pair of position? I need to block it so that it's gonna be forced into the Ortho. On top of that. Ideally, this should be a meta director when I add the anally because I wanted to be synergistic with the Ethel Group to face towards the top. So I should be thinking Are there any groups that I could add that could be a meta director and then be turned into a North Opara, Director Later. Okay, so that's one thing. Another thing is, do we even know how to add an a lien toe? A benzene did ever teach you how to add N h two specifically to a benzene. And it s reaction. No, but did I teach you a precursor that could be easily turned into Annaly? Yes, Guys, remember reduction of nitro groups. We can use nitrates shin to make anally, which is why it's so popular. So at some point, I need to nitrates that position. But Onley after I already have some kind of meta director in this position, see where this is going? All right? You might not, but let me just step in and try to help. And, guys, this is just you have to just start getting a feel for these. Okay? So the first direction we're gonna do is ah Friedel crafts Ace elation Because we know that ace elation can be turned later on in tow. Calculation. Okay. In tow, using a Clemens introduction. So I'm gonna use I'm just gonna race this. I'm gonna use an acid chloride Now. This part is important, guys, your acid chloride needs to contain the number of carbons that you want in your end product. So since I'm adding it here, how maney carbons should this acid chloride have just one? Because I only have one carbon here. That means that I should have an h on the other side. Because I only want one carbon total. That's the carbon on the carbon. You'll I'm gonna combine that with L C. L three and I'm gonna get a molecule. Looks like this. Okay, now see Saigon Alga High for right now. Notice that it attached to the para position because we said that pera is pretty much predominantly favored. Especially when you have larger groups like a seal groups. Cool. So now what can we do? Well, now I have a meta director here and an Ortho Parra director here. Now is the time to nitrate because they're both synergistically pointing to that top position. So now would take my nitric acid and my sulfuric acid And I would now make my night traded my nitro group along with my Al hide the bottom Cool. Awesome guys. So now what do you want to do? What we have. Two more things have to do we have to do a Clements in reduction and we need to do a nitro reduction. Okay, Now, these use slightly different re agents, so I'm just gonna draw both of them, and it doesn't really matter the order because both things need to happen, and we don't have any more groups to direct. So if you chose to do Clemmensen first and then reduce the nitro, that's fine or the other way around, Let's just do that. So let's do Clemmensen Zinc Mercury amalgam with HCL. That's going to give me a single carbon with an n 02 Okay. And then finally, I would use any of my reducing agents that work on nitro groups to turn into an anally again. I've told you as a few times now I prefer standards chloride s N c L two and H 20 Because that's the one that's chemo selective. If there was anything else here that could be reduced, it would Onley react with the Nitro group, and that's going to give me my final product. So this was a four step reaction and we got it. We have figured it out. Okay, so you see how sequence groups are so important. Awesome guys. So let's go ahead and move on
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Problem

Provide the reaction for each of the following reaction steps

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Problem

Beginning from Benzene, synthesize the following compound.

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Problem

Beginning from Benzene, synthesize the following compound. 

1-Phenylethanol

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Problem

Beginning from Benzene, synthesize the following compound.

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