We use Newman projections to visualize the rotations of conformers. Some are more stable than others. Let's take a look.
How sigma bond rotation is visualized
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now that we understand that signal bonds are free to rotate as much as they want, It turns out that there's a unique way to visualize this rotation. And that visualization technique is called the new and projection. Alright, so new and projections are all about finding the different energy levels that conformers could make by rotating a Sigma bond. Okay, so maybe you recognize this drawing This drawing is the same drawing that I had before when I was talking about Conformers and I was saying that you could have and s trans hex seen or esus heck saying okay. But it turns out that it's kind of difficult to visualize how those air different and energy energy is kind of ah, abstract concept. Right now, we haven't really defined it very well, but just think about it that if something is very high end energy, that's not gonna make it very stable. Okay, so in this case, it's not easy to tell which one is lower energy and which one is higher energy. And that's why we wanna have a new way to visualize this. So what we say is, hey, imagine that your eyeball was right on this plane. So imagine that this is your face and this is your nose and those your lips. And obviously you're just amazing looking, dude. Wow. Okay, so I need to, like, stop what I'm doing, because that's really terrible looking. So imagine that that's a person. Don't Don't imagine that to you. I don't want to get traumatized. And you're looking at that bond straight down the line straight down that bond. What you would actually see is you would see a carbon in the front. Let's say, Ask your red carbon and you would also see a carbon in the back. Let's say that's your blue carbon. You would see them overlapping each other. You'd see one. If you're looking right down that bond, you see one in the front one in the back so you would see that this will be your front one. And then the one in the back would be represented by that circle. Okay. And basically what Newman projections allow you to do is to visualize. Okay, where are the groups on the front carbon oriented and where the groups in the back carbon oriented and how are they related to each other? and you're with Newman projections. You're allowed to rotate around that bond in three dimensional way. Okay, So basically, if you were to look down that bond, what you would see is that your big groups, this ethel group here and this Ethel group here would be on opposite sides of these carbons because, as you can tell, if you were to draw your dotted line, they're on opposite sides of the fence. So basically, they'd be really far away from each other. Okay, But then if you look at assists, esus is different. Esus If I had the same thing where my eyeballs looking, I would still see one in the front. Just second. Wow, Red. I would still see one in the front and one in the back. But what I would also see is that now the big groups are overlapping each other. Okay, Instead of being on opposite sides, they're overlapping. And that has a huge difference in how stable these molecules are. How stable these confirmations are.
So Newman projections are way of analyzing which sigma bond rotation will be the most stable. We have some rules about which rotations are better and which are worse!
Three Types of Conformations
The dihedral angle (theta), is equal to the angle between the two largest groups on either side of the projection.
The energy states of 3 different Newman Projections.
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So let's go ahead and start off by defining what the dia he'd roll angle is okay. The DIA he'd roll angle is defined by theta. Okay, so theta is just a variable. That means England. Okay. And what it does is it describes the rotation between the two largest groups relative to each other. Okay, so basically the largest group in the front on that front carbon largest group on the back carbon where they are relative to each other, that's gonna tell you your diary drill angle. So, for example, if my two largest groups are overlapping each other perfectly like that, Okay, By the way, I just want to point out that there is a mistake on mine. How? It says ch three should be ch two on then ch three. So don't let that freak you out. Okay, So anyway, so if they're perfectly overlapping, that means that the difference in their angle is zero. Because as you go further around, your angle gets bigger, but they're perfectly overlapping. So the diet usual angle in this case would be zero. And this confirmation is called eclipse. Okay? And the eclipse confirmation is the one where both of the group's overlap each other perfectly. Okay, this happens to be the confirmation with the highest energy. Okay, Why would that be? Well, it turns out that large, bulky groups don't like to be next to each other. Why? Because they feel crowded. Remember that big, bulky groups, They don't just have atoms. They also have electrons, and electrons are negative. So if you put a bunch of these electrons together, they're going to repel each other. So it's a really bad idea for these groups toe overlap each other so perfectly. So this is gonna be highest energy. And what that means is lowest stability. Okay? Energy and stability are inverse of each other. Okay, They're opposites. Okay, so then let's look at the next one. The next one would be if the diarrhea angle is 60 degrees, 60 degrees just means that they are not perfectly overlapping, but they're also not perfectly far away. They're just, like, kind of like, you know, maybe like a I don't know, like, two o'clock. Okay. And at a 60 degree angle, Um, that is going to be called a weird word that's gonna be called Gosh. Okay. And gosh, is just you could say it's when they're adjacent to each other. They're not overlapping, but they're still not as far away as possible. So in this case, you see how it's visualized. There. Now, this one is knots. Amazing. But it's not as bad as the other one. Okay, so what I'm trying to say here is that the gosh confirmation. It's not as unstable as eclipsed, but it's also not as good as it could be. So I'm just gonna say, here it has, like, middle energy, okay? And that's a terrible word to use. Okay, but middle meaning just that it's not as bad as eclipse. So that would also mean kind of like middle stability. Okay, cool. So now we're gonna go onto our last one. Our last one is what if the diarrhea angle is 180 degrees? That means that they're perfectly apart from each other. Okay, If they're perfectly apart from each other, that means that they're the furthest way they can get. And that means this is gonna be called anti or anti. The anti confirmation and the anti confirmation is where your two largest groups are opposite. That one's gonna be the lowest energy. And by lowest energy, that would obviously mean most stable
Plotting a Newman Energy Diagram
As you’ll see, when we plot (theta) against energy, we wind up getting a predictable pattern of peaks and valleys that can be used to better understand the different rotations.
How to draw a Newman Projection Energy Diagram.
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So what I want to do is I want a plot, an energy diagram with thes degrees. And I want to show you guys what that means and how that actually translates. Okay, Now, I know this is gonna be your first interaction with an energy diagram or one of your first interactions, so I'm just gonna explain how this works. All right? Energy is on the Y axis over here. And as you go up, you basically get less stable. Is that cool on? Then, on the x axis, I'm gonna have the DIA. He'd roll angle. Okay, so I'm gonna go ahead and start off at zero zero degrees, and then I'm gonna go by groups of 60. So I'm gonna have 60 1 20 1 2 40 300 and then 3. 60. Is that cool? All right. So what I want to do is go ahead and start off. We don't have numbers, and I don't want you toe worry about exact numbers. I just want to get a general pattern of what this is gonna look like as it rotates. So, basically, what I'm doing is I'm drawing a map off. What? The energy and stability. Looks like as this bond rotates a full cycle or whatever. Okay, so let's go ahead and start off with 00 degrees is what kind of energy is it? Highest, Lowest middle. What is it? Zero degrees is eclipsed. That means that they're perfectly overlapped, which means that this is gonna be the highest energy. So I wanna pick a point that's really high on my energy diagram. Do I need to know exactly what energy? No, I just wanna pick a high point. Is that cool? Now, let's look at 60 degrees. 60 degrees would be. Gosh, we said that Gosh is more stable, then eclipse. So what I should do is I should pick up a spot that's lower, so I'm gonna pick a spot, like, right here. All right. So that means that as I rotate from 0 to 60 I'm getting better. My energy is getting less. Which means that my I'm also getting more stable. Is that cool? All right, so then we go toe 1 20. Okay, Well, actually, let xgo one 81st. Since that's the one that we actually have plotted out. And then we'll go one. We'll do the one twenties. Okay, so for 1 80 1 80 would be that they're perfectly far apart, which means that they're the most stable that it's ever going to get. So 1 80. Where should I plot that point? I should plot that point at the lowest point of my graph. That's gonna be the most stable point on my graph. All right, cool. So then let's go ahead and plot Thies again for if we kept going. So if I basically if I added another degrees, I would get back to the 60 degrees spot, but I would get to the 60 degrees spot the other way. And then finally, after 360 degrees, I would get back to a full cycle where they're overlapping again. So then I would pick a high spot. Okay, Now I know that it's difficult to visualize what? That maybe that second blue spot looked like. So I actually draw it. So remember that this first read one would just be like this. It would be, Let's say you have X and X and their overlapping Okay, so that would be our and then you have basically all these early ages. Okay? I'm just writing X because I don't want to draw the entire thing, Okay? Actually, yeah, that's fine. Well, actually on it says here to plot drug down the C three C four bond of heck seen. Okay, What does that mean? We should actually talk about that. I'm sorry. I forgot to mention that. Okay. What that means is that they want us to show down the bond of the third Carbon in the fourth Carbon. What the different energy levels would be notice that what's coming off of the first half would be an ethyl group. And what's coming off of the second half would be an ethyl group is well, because the two in the middle are the part that are in the Newman projection. Those two are the front and the back of the Newman projection. Okay, so what that means is that I could just instead of writing x X, I could just right e t e t where e t stands for Ethel. Okay. And that's actually really common abbreviation of Ethel is just to write ET. Okay, now let's go down to 60. 60 would mean that now one of the Ethel's is still facing the top. But now the other Ethel is to the side. Does that make sense? Cool. So another a little bit more stable than 1 80 would mean that one ethyl is facing up and one Ethel's facing down. Okay, well, then where am I getting this other blue spot from? While the other blue spot would be if I just continued rotating this. What I would eventually get is that this it is still the top. But then now this ET just got 60 degrees away again. But now it's on the other side. And then finally, this one would be, if the overlap again. All right, So now you're probably wondering, with one twenties with 1 20 is actually don't have a name that we use often in organic chemistry. But you could imagine that What's happening is that the one twenties I'm gonna get a e t here. And then I'm also gonna get an e t here overlapping with an H h h. So that means that for the one twenty's, everything is overlapping again. Okay, so that means this is actually gonna be a higher energy point. So this one would actually be appear somewhere. And then this one would also be appear somewhere. Okay, so now we finally got our energy diagram. All we have to do is connect the dots, and when we connect the dots, we're gonna get something. Looks like this basically down here, then up. Send down, then up, then down. And then back up. Okay. And that is your energy diagram as you rotate along the bond. What that basically says is that you start off with worst spot, then you go 60 degrees and it gets a lot better. Then you go 120 degrees. It gets worse again. Then you go 1 80 it gets the best thing. You come back and you do to 40 and that's pretty bad because everything's overlapping. Then you do 300 that is a little bit better than 2. 40. Because now things air staggered. And then finally, 3 60 is the same. A zero. Okay, I know it looks silly with me during the whole clock thing, but hopefully that helps you guys relate to this diagram. Now, the reason I went in such depth with this diagram is that some professors want you to be able to draw this or at least recognize what's going on with these dia hydro angle diagrams. Okay, so I just want you guys to understand that hopefully now you should easily know that anti is the best. Eclipses the worst and gosh is in the middle, and you should also be familiar with their diet federal angles.
Professors may ask you to draw this, so don’t just tune it out! You need to understand the basics of energy diagrams for this topic.