Hey everyone, it's Casey from the Montreal Student Network and today we're going to be looking at axial and equatorial cyclohexane planes. More specifically, we're going to be looking at how to draw the chair conformation when you're asked to look at a specific problem. I have some examples that we're going to be looking at later on in this video, but first we're going to start off with the basics.
This is the chair confirmation. I'm not going to go into too much detail on it, but the different planes I have laid out, the ones that are in pink are the axial planes, and traditionally axial planes are going to be less stable and less favorable if you have a big substituent on that end, because it puts you in contact with other parts. It's not like the equatorial ones, which are in green, which point away from the structure.
Those will give you more space. If you have a bigger structure... that's going to be attached there, it will be more favorable. Now, remember, like we've seen last video, there are going to be some of these that are pointing upward and some of them that are going to be pointing downward.
And you want to take this into consideration when you need to look at cis and trans relationships. So we see that the ones that have the little blue crosses on them, little blue stripes, will be the ones that are pointing upward. And we see that we have three axial pointing upward, and we have three equatorial that are pointing upward.
Now, this is very important to take into consideration when you're looking at cis and trans relationships. because if you have, say, these two substituents that you want to place on. Say you have the really big tertiary butyl group, which we see how much space that takes up. And then say you have a little methyl group. Now, clearly, this one takes up a lot more space, and you'd want to give that one the preference of being on the equatorial axis.
So if you do have a selection between putting one on the equatorial and one on the axial, you're going to want to put the biggest and bulkiest group there. Now, this will be typically in problems that look something like this. So we're going to jump in right to the examples, not to waste any time.
Draw the most stable chair conformations for the following structures. Now, it's going to say most stable. That's going to be the keyword right there, and that's when you're going to know this is where you need to distinguish axial from equatorial.
So we're going to start off by looking at the first one, which is cis1. Tert or tertiary butyl 3-methylcyclohexane. Now if you're wondering why the T comes before the M, when you're looking at stuff that's not a butyl group, you're only going to want to look at the B.
So B comes before M. That's why the butyl comes before methyl in the naming. So we're going to draw out a chair conformation.
You can pick whichever one you prefer. I like to draw them this way or you can draw the flipped way. But I find this is easier because it looks like an N. So it's a bit easier to draw it out.
Now we're going to see we need cis-1-tert-butyl-3-methylcyclohexane. So what is this telling us? This is going to tell us from the numbering, first off, from the 1 and the 3, that there's going to be a space between the branches.
And the cis is going to tell us that they're going to be pointing in the same direction. So let's go up and look at our diagram that we drew before. And we see that we are going to need to, number 1, first step, before you even look at any of the things, you're going to want to identify what the most bulky group is. So methyl, like we saw up here, methyl is over here, it's pretty small. So the bigger bulky one will be the tertiary butyl group.
So we're going to automatically want to put the tertiary butyl group on the equatorial plane. That's your number one priority. So say we use this one right over here. This is pointing upward because it has these strikes on it, and it is equatorial plane, so we can put our tertiary butyl group right over there.
Now since we have it's a 1-3 relationship like we saw, there's that one little spread between them, we're going to go and we're going to move over two spots. It doesn't matter which spot we pick. Both of them will be the same. So we can move one and then we move over here. This is where our third spot would be.
If this was number one, carbon, this would be number three. Now we can see that it needs to be pointing in the same direction. That's the only thing we're going to look for. We're not looking for axial or equatorial because it doesn't matter at this point. We have put the important one in its position.
And we see that the upward position happens to be equatorial. So it's a double win, even better. So to go in, we can draw out our structure right over here. We would have over here, try to fit it in. That's the abbreviation for the tertiary butyl group of C with a CH3 to the power, well, in brackets with another 3. Coincidentally, we'll have our hydrogen on the axial plane.
And over here, we'll have our methyl group end right there. So we see in this case, we have both of them on the equatorial plane. That is maximum stability, maximum happiness.
Now what happens if we don't get such so lucky? We see in our next example we have a 1 and then we have a 2. Let's get the different color out. Now what does this mean?
Well, we can go back and look. It actually alternates between which one is pointing up and which one is pointing down from the axial to equatorial as you go along. Now unfortunately, the one that's pointing up is in the axial plane, which is less stable than the equatorial plane. Now what do we do in this situation?
exact same thing as we did in the previous one. You want to follow this specific chain of steps when solving any stable confirmation question. If you follow this chain of steps, you'll not run into a problem. So first, identify what the bulky group is.
Like we said, it's normally going to be tert-butyl because that's the one everybody really knows. They're not trying to find if you know which group's bulkier than the other. They're just going to see if you know how to solve a certain problem like this. So first, tert-butyl. Now, before you look at anything, before you look at the numbers...
go and put that tert-butyl on an equatorial plane. I like to start with this one because it normally gives me a lot of space to draw. Three right there and there is the tert-butyl group.
It's on the equatorial plane. Before you do anything else, now you're going to want to look at what, where is the other one, where can the other one be found? We see it can be found on the second carbon which will be the next carbon and you can pick which one you want to do.
So we're going to go over here and At the second carbon, we've identified where that is. Now we're going to want to look at what the relationship is. It's cis.
They need to be pointing in the same direction. Let's go back up and look at our little diagram. The same direction, unfortunately, it's in the axial plane.
So we're going to abide by that rule, and we're going to go, boom, axial, CH3. And there's our methyl group, and we can put our H coming off right there. You need to follow those steps.
You can't just go and see, okay, let me try to put both of them. You know, they're not going to both fit in the same one. In the situation where they're both on consecutive carbons, they will not be able to go on the same plane unless it's a trans relationship. It does alternate. So that's one thing you want to look into.
And you really want to follow those steps. So always, always, always, like even write this down. Like, I don't know, write this down in a piece of paper or in your notes, write it on the front of your book.
Always look for the bulky group first. Bulky group. First. Always. No exceptions.
Go look for the group first, put it in the equatorial plane, and then work with what you got. That's the best way to solve this. It's not going to run into any problems, and I guarantee you these problems will go back very, very quickly.
You know, you go by them quick, don't spend too much time on them, and you'll be able to brush by them real easily just by following those steps that I mentioned, and always look for the bulky group first. So that's the video. I hope you guys enjoyed, and if you have any questions, feel free to leave a comment or contact me on Twitter. I'll leave my Twitter handle in the description so you can always send me a message.
It goes straight to my phone and I can answer you guys as soon as possible. So thank you very much for watching and I hope you guys have a great day.