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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.

Table of contents
16. Conjugated Systems

Diels-Alder Reaction

The Diels-Alder reaction is a heat-catalyzed, reversible pericylic reaction between a conjugated 1,3-diene and a dienophile


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in this video, we're going to discuss the most famous Perry cyclic reaction in organic chemistry. And that's called the deals All the reaction. So the deals elder reaction is a heat catalyzed reversible Perry cyclic reaction between two different molecules that we're going to go into more depth on. Okay. Now, the one thing in common between all deals, all the reactions is that there always gonna yield a six member ID ring as their products. So you always know that you're going to create one new ring through the formation of a deal's elder reaction. Okay, so we need to components plus heat. To make this happen, we're gonna need one. A +13 dying two. We're gonna need a dying of file. Now, I recognize that these air terms that you're probably not that familiar with, So it's really just dive into what that is. Okay, so first of all, a 13 dying is pretty simple. It sounds like exactly what you're thinking. It's a dying that is that the one in the three position. So basically another way to say it is that it just has to be a conjugated dying. Okay, because if it's not 13 Let's say that we used a 14 dying then that would no longer be a conjugated dying. We would actually call that an isolated dying because now the double ones wouldn't be next to each other. They would have a space in between. So you can't use a one for dying that z isolated. You need to use a conjugated dying. So let's look at some examples. This first one is pretty easy. That looks like a typical dying. Um, you can have any other are groups the important things that you at least have that 13 dying here. You see that we actually have a cyclic in the middle. We have a cyclic 13 dying because one of them starts with one and one of them starts to the three. You might be wondering Johnny Weir using those specific atoms to count as one and three. It doesn't matter where you start as long as you have dying, starting basically two carbons away from each other, right at the one and at the three of two dying to double one starting. So that's another dying. And then here we have another example of 13 dying. So I'm just trying to show you guys how 13 dying's can come in. All shapes and sizes were just carrying about the fact that they're conjugated to each other now. What's a Diana file? Well, by definition, the word file means lover. So Diana file would be a molecule that loves dying's. So Diana files are actually really easy. All they are is that they are Al Keene's or all kinds. That's it. It's really that easy. So here, a Diana file could just be a simple cyclo hex pain. Just having that double bond there because the Diana file now notice that this next molecule here has two double bonds. Which part of it do you think is the dying of file? Well, I said, in the definition, it has to be an Al Qaeda and Al kind. So this is actually the Diana file. Nothing else. The Carbondale doesn't count. Check this out. That's weird. Did I make a mistake? Did I drag the wrong molecule the same molecule to this box? No, I didn't, because it turns out that Dying's have al kids in them, right? So that means both of these double bonds can act as dying of files. That means you can sometimes see diamond ization taking place with these reactions. Where one molecule reacts is the dying and the other reacts is the dying of file, and they react together to form a dime er or something that there's two of now attached to each other. So that's something we're gonna be aware of. And then here's our last example. Triple bonds have pi bonds in them, so this can also be a dying a file. Alright, so pretty simple. So far, we know that we need a dying a 13 dying. We need a Diana file. We need heat because I told you it's a heat catalyzed reaction. But it turns out there's a few more technicalities you have to go over before you're ready to draw these. So one is that your 13 dying has to be in a certain shape. You can't just use anyone. Three dying. The 13 dying has for the mechanism toe work. You're gonna need to have your 13 dying rotated into what's called the esus or Sigma sis. Confirmation. Now remember, from organic chemistry one that Sigma bonds are able to freely rotate as much as they want, meaning that just because it's in that position now doesn't mean it will always stay there. We have to make sure that at least it's able to rotate into the esus confirmation momentarily. Let me show you what I mean. This dying okay is not rotated into esus. This is what we would call s Trans. Why? Because if you were to draw a dotted line along the single Bonder the Sigma Bond, right, what you would find is that your are groups are on opposite sides, right? So that's what we call s Trans. Because you're Sigma Bond is rotate in such a way that they're on opposite sides. Okay, now, if we were to rotate that Sigma Bond, what we would find is that now, when we draw that same line now they're on the same side. This is what we would call esus. Okay. And this is the way we needed to be rotated. So this would be a big No, no, You can't start off like that in order to begin your deals. All the reaction you must rotate it first into the esus and then you can proceed. Not that bad. Okay, Now let's look at the general mechanism. The general mechanism is gonna be an s sis dying, right? Specifically esus one. Let's get it right. 13 dying right with the Diana file. Remember, I told you guys that a Diana file could be any al Qaida Al kind. So this molecule right here is a perfect diana file because it's just got that double bond. So the cycle ization reaction is a three members or three arrow reaction where you would get the Diana file initiating, because, remember, it's like the lover of the dying, so it just wants to attack it. So I would go ahead and I would attack one of the edges. Okay, but if I make a bond, I have to break a bond because I'm in violation of an octet. If I don't, So then this double bond is going to make a new double bond here once again, make upon break a bond, I'm gonna need to break that last dying. So this one comes over and attach is to the other side of the double bond. This is gonna form to new signal bonds this forms a new single bond here, and this forms a new single bond here. And then this arrow that's going in between the diets forms a new pi bon here. Okay, so our final product has two new bonds and a double wand. And as you can see, I now have a six member product. Okay, six members cyclic product. Cool. So far, that's the general mechanism. Now there are a lot of you could get a problem that's just that easy, but deals Alder can get a little bit more complicated as I'll show you guys. And I'm going to start layering on the complications, the first of which, being it's pretty straightforward that the stereo chemistry of all substitue INTs must be retained. So you have to identify the stereo chemistry of your Diana file, and you're dying so that when you react this together and make a ring that the Steri chemistry is preserved. So check out this aerate this first deals alter, we have a 13 dying, dying and a Diana file. But notice that my our groups on this Diana file are in a cysts position. This would be a cyst. Alky right remember, double bonds don't twist. So it's always gonna be cyst. It has. It can't be Trans. The way we can tell it, sis, is if we were to draw that dotted line or fence that I like to use their both on one side of it, Right. Well, when we react this product, we're gonna draw our arrows. When we react this product, you need to make sure that your are groups remain cyst to each other. They have to remain on the same side of the ring. Now, Did I have to face them up? No. I could have also faced them down. The important part is that they're both facing the same exact direction. It wouldn't make sense if I put one are up and one are down because that would look like trans. And that's not what I began with, right? Awesome. So that's pretty straightforward. In the same way, if I begin with a trans double bond, as you can see, this was different. Then I'm going to get a pair of Ananta MERS because I'm just gonna take myself out of the screen because, as you can see now, I'm going to get Trans products. But there's two different ways that those trans products could orient each other I could get are one in the front, but I could also get are two in the front, just depending on how the attack works. So in this case, I would have to draw a pair of an anti MERS because I have two different trans products that are possible. Okay, so this is just really basic stuff. You have to make sure you get right. Um, and make sure you pay attention to the stereo chemistry in orderto get the full credit for this question. Okay, so pretty easy so far, but that's not it. There's a few more complications with deals older, so let's go ahead and move on toe a few more concepts.