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Current time:0:00Total duration:11:27

Video transcript

- [Voiceover] Let's get some practice drawing chair conformations. One way to do it is to start by drawing two parallel lines that are offset from each other, so let me go ahead and show you what I mean, so here's one line and then here is another line. They're parallel to each other but they're offset a little bit. Next, we're gonna draw two horizontal, dotted lines, so the top horizontal dotted line is going to be on level with that top point there, so, I'm just gonna draw a dotted line here. I'm gonna draw another dotted line down here, which is gonna be level with this bottom point, so that's what we have so far. Next, we're gonna draw in another set of parallel lines. We're gonna start at this point right here, where this intersects with the dotted line, and we're gonna go from the top dotted line down to the bottom dotted line like that, and then we're gonna try to think about drawing a line parallel to that over here, so we're starting at this dotted line and we're going up to this point. And then finally, we need to connect the dots, so we're gonna go from this point to here and then from this point to here, and that's our carbon skeleton, so if you draw this properly, you should have three sets of parallel lines for your carbon skeleton. Let's go back up to this drawing here, and let me show you those parallel lines. So we started with this set, so this bond, and this bond, that's what we started with. Next, we drew in, let me change colors so you can see, we drew in this set of parallel lines, and then, finally, we drew in the last set, so let me highlight those in blue, so this line, and this line are parallel, so that gives you your carbon skeleton, and next, you need to think about putting in your groups. In this case, we're talking about Cyclohexane, so we're only dealing with hydrogens, so first, we're gonna put in the hydrogens that we call axial or axial groups here, and axial groups, you can think about the earth, so here is the earth, you can think about this as being a globe and this would be the axis going straight up and down, so hydrogens that go straight up and down are called axial hydrogens, and we're gonna start at this carbon right here, which I'll call carbon one, so if this is carbon one, we're gonna draw in an axial hydrogen, so this is going straight up. Next, we're gonna go to carbon two, so this one right here, and straight down would be an axial hydrogen. We're gonna go to carbon three and it's straight up for an axial hydrogen. Carbon four is straight down for an axial hydrogen. Carbon five back here would be up, and then, carbon six would be, would be down axial hydrogen. So you can see that we alternate. If we start at carbon one, we start up axial, so let's go ahead and put in the axial hydrogens on our Cyclohexane, on our chair conformation. So here is carbon one. We're gonna draw a line straight up and put in a hydrogen. We go to carbon two. We draw a line straight down and put in a hydrogen. Carbon three, we draw a line straight up and put in a hydrogen. Carbon four, we draw a line straight down and put in a hydrogen. Carbon five would be up, so we put in that hydrogen, and finally, carbon six, would be down for our hydrogen. All right, next, we need to think about the equatorial hydrogens, so that would be, starting at carbon one, that would be this hydrogen right here. Carbon two, it would be this hydrogen. And they're called equatorial because you could think about them as being along the equator of the ring, so if this is the earth, we know that this is the equator. So these are kind of out to the side, and they alternate too. At carbon one, this equatorial hydrogen is down relative to the plane of the ring. At carbon two, this equatorial hydrogen is up relative to the plane of the ring. So we start down and then up, and then at carbon three, this would be down. At carbon four, this would be up. At carbon five, this would be down. At carbon six, this would be up, so just imagine all of these hydrogens are along the equator of the ring. So let's put in those equatorial hydrogens into our chair conformation. We start at carbon one and we start down, so down equatorial, so we draw a line down here and put in our hydrogen, and then we go up. So at carbon two, it would be up, so we put that in. We alternate, so at carbon three, it would be down, so we draw in that hydrogen. At carbon four, it would be up, so we put in that hydrogen. Carbon five would be down, so we put that one in, and carbon six would be up, so we put that one in. These are the ones that students have the hardest time with, so you could think about the parallel lines that we drew earlier to help guide you. So let me go ahead and show you what I mean. So we started with the parallel lines in yellow over here, so if you look at those lines, you should have, you should have these, right? These are also parallel. So this one is parallel and this one is parallel. Also you could look at the ones in red next, so let me highlight those again, so this set of parallel lines, these two right here, so that would be these hydrogens right? Or these groups, I should say. Those should be parallel. And finally, let's look at the ones in blue. So let me highlight those again really quickly. Let me use a darker blue so we can see it a little bit better, so this one and this one, right, those were parallel lines. Well, we can also see that these, right, these would be parallel to those as well. There's another way of thinking about this which might be helpful. If you look at the drawing on the right, I'm highlighting some of the bonds in magenta, and when I'm done, this should look familiar. You've seen this before in the video on conformations of ethane. That was a sawhorse drawing for the conformation of ethane, the staggered conformation. Let me draw it over here so you can see it a little bit better. So, here we have the staggered conformation for ethane and that's helpful sometimes when you're thinking about how to draw the different bonds in the chair conformation. So pretty much, you can use any method you want. I've seen lots of ways to draw chair conformations, and lots of students come up with their own way of doing it, so whatever works for you, just be consistent and be careful. Take your time and you have to practice a lot. Next, let's look at another chair conformation that you'll be drawing. We need some practice drawing the other chair conformation. We're gonna start the same way we did before with two parallel lines that are offset from each other. This time, though, the lines will be going in a different direction than what we did before. So let's go ahead and put in one parallel line. So there's one, and then another one, like that. So hopefully those are pretty much parallel, and then we're gonna draw in a dotted line, a horizontal dotted line that just touches this top point here on this top line that we drew, all right? And these dotted lines, remember, are just guidelines. They're not actually a part of our chair conformation. We draw another dotted line down here that intersects with this bottom point, all right, as our guideline. Next, we go from the top dotted line down to the bottom dotted line. So from the top down to the bottom, and then we go from the bottom back up to the top, and finally we just connect the dots, so from this point we draw a line to here, and then we draw that line again, a parallel line at this point, to this point. So make sure that everything is parallel. You have three sets of parallel lines. The first set of parallel lines we drew was this one up here, on the drawing, so in yellow. Next, in red, we went from this point down to this point and then we went from this point up to this point, in red. Those should be parallel. And then finally, in blue, this line in blue should be parallel with this line in blue, so make sure you have three sets of parallel lines to draw your carbon skeleton. Next, this turns out to be carbon one, right here, and we'll see why in the next video. So we're gonna start to put in our groups. In this case we're just gonna put in all hydrogens, and at carbon one, you can see that we're starting axial down this time. So we're gonna put a hydrogen axial down. That's the opposite of what we did in the other chair conformation. At c-one in the other chair conformation, we started axial up, so we're gonna start axial down, so we put a hydrogen going down at this point, and we move over to carbon two. So this is carbon two right here, and you can see, now we have axial up for our hydrogens, so we go to carbon two and we have axial up. Carbon three would be this one. You can see it's axial down, so carbon three is axial down, and again, this just alternates. So carbon four should be axial up, so we draw in our hydrogen going up at carbon four. Carbon five, axial down, so we draw in our hydrogen here, and finally carbon six is axial up, so let's put in that hydrogen. Next, we put in the equatorial hydrogens, which are a little bit harder to draw, so let me use a different color here so we can see. Actually, let me go ahead and keep it yellow because this equatorial hydrogen, right, is parallel with this set of lines, right, and also this one over here actually, so we're doing equatorial up for our first hydrogen, so this line is directed up relative to the plane, so that's how you have to think about it. So we start at carbon one and we go equatorial up, so we put in that line and put in the hydrogen. Next, at carbon two, we already had this hydrogen going up, so this must be equatorial down, so we have equatorial down, and this line should be parallel with the ones in red, right? So this line should be parallel with the ones in red that we've already seen, so let's put in that hydrogen. All right, so this is equatorial down. At carbon three, we have equatorial up. Let me use a different color. We have equatorial up at carbon three. I used blue because, again, with these lines parallel in blue, so we have equatorial up at carbon three. Go down to this drawing, let's put it in, so here is our hydrogen going up. And again, we're alternating. We start at equatorial up, then equatorial down, let we draw in that hydrogen, and then equatorial up, and then equatorial down is our next one. So equatorial down at carbon four, and then carbon five should be up, so here it is up, and this should be parallel with the ones in red. This is one of those ones that's difficult for students. Again, it's parallel with the ones in red, so that should make it easier. So let's draw that in, so we have our hydrogen going up at this point, and then finally, carbon six. You can see this is equatorial down, and I guess it should be blue, so let me be consistent here. So this is parallel with everything else in blue. We have another hydrogen, which is equatorial down, so let me draw that one in, so. Actually, that wasn't very good, so let me do it again. This takes practice, right? Keep practicing your chair conformations, both kinds of chair conformations.