Understanding Cyclohexane Conformations

So in this video we're going to talk about the interconversion of cyclohexane of confirmers cyclohexane confirmations. So let's get started. We know the cyclohexane ring it has a six carbon atom so six carbon-carbon single bonds and usually cyclohexane rings are stable ring and it because it can adopt it can be in chair confirmations. If the cyclohexane ring appear in chair conformation, there is no torsional strain. So the ring is very stable. The thing is right here, since all this carbon here and also all the carbons here connected by carbon-carbon single bonds, and we know the carbon-carbon single bond, they can freely rotate. And because of the result of simultaneous rotations about all carbon-carbon sigma bond, usually the chair conformation of cycloexons can inter... convert to another chair confirmations by ring flip. So you can see here if this chair confirmations if they rotated about all carbon-carbon bonds they will take the shape of another chair confirmations shown it on the right. The way that we usually take a look these ones if you just push this carbon this down carbon up and this half carbon down then you will have a ring flip chair confirmation. So this two are the chair confirmations and since this is obtained by ring flipping of this chair confirmations we call ring flip chair confirmations. Again, usually what we do we can we put we push this down carbon up and then we pull the down carb we pull this carbon down so that's why we get the ring flip chair confirmations. So in this process what actually happened you also can see here well the equatorial bond they turn into an axial bond and axial bond that they turn into an equatorial bonds. So in this process when when there is a ring flip in chair conformation equatorial bonds become axials and axial bonds become equatorial. Now how to draw a ring flip chair conformation. So Usually there are three rules and you must need to remember these three rules in order to write the ring flip chair confirmations. First is draw the mirror image of your original ring. So this is your chair confirmations. Let's say you have a substituent R on this up carbon and pointing axially. So you have XLR group. So if according to the step one, he says, draw the chair confirm, draw the mirror image of your ring ring. original ring. So in order to do that, what you have to do is just kind of pull this carbon down and then push this carbon up. That way you will have the ring flip chair confirmations of the original one. So you know, so when you do that, so we have now the mirror image of your original ring. The second rule you can, you can see here the up carbon they turn into now down carbon and down carbon turn into up carbons in the in the ring flip chair confirmations now step two says on your new ring move every substitute one position clockwise or counterclockwise it doesn't matter which way so if you number these two carbons one and two and now you just kind of on your new ring As it says, move every substituent in one position clockwise or counterclockwise. So we move every substituent by one position this way. So now I have my up carbon turn into a down carbon, and down carbon turn into an up carbon in the new ring. That's what it says here. Now what we see step three says, draw each substituent on a new position. It was on carbon number one, now it's the carbon number one. If it was equatorial before, then make it axial on the new ring. If it was axial before, then make it equatorial on the new ring. So we have here the axial, so that means this is going to be equatorial. So axial become equatorial, equatorial become axial, and another thing up. So this is up carbon. as a half-substituent will remain as a half-substituent. If you have a down, then it will remain as a down, right? So these three steps you need to follow in order to draw the ring flip chair confirmations. Again, the first is draw the mirror image of your original ring by pulling this carbon down and pushing this carbon up. And then on your new ring move every substituent one position clockwise or counterclockwise. It doesn't matter anyway. And then Draw each substituent on its new positions on your new ring. And remember, if it was axial, then that will turn into equatorial. If it was equatorial, it will turn into axial. And up stays always up, down stays always down. Now, let's solve a problem together. So that way you should be able to, you should be able to draw a ring flip-chair conformation. So here is that we want to draw a ring flip chair conformation of these molecules. Again if you like you can pause the video and try to draw the ring flip chair conformation on your own. Then you can check your answer with them. So I'm going to show you in a second. So first rule is it says I have to draw the mirror image of this original ring. In order to do that What I'm going to do, I'm going to pull this one down and this one up. That way I'll have my mirror image of this original ring. Now if I number this one, this is one and four, then my new carbon, the carbon number one is with this one and the carbon number four is that one. Usually up carbon turn into down carbon, down carbon turn into an up carbon. Now I have to have these two substitutes on carbon number one and carbon number four. I don't know what would be the position of those two. However, I can see the rule number, step number three says if it was equatorial here, as you see, if it is axial here, then it will turn into equatorial. If it is axial here, it will turn into equatorial. So I will have two equatorial. So this substitute in here is going to be equatorial, this substitute is going to be here equatorial. So then I completed my drawing the ring, flip, check, confirmations. So what I did, if I summarize here, I have the mirror image of this original ring, but I pulled this one down, pushed this one up, so then that way I'll have my new mirror image of the ring. Then I move one, move the substitutes, move the substituents counterclockwise this direction. So I have one and then this is four new position of carbon number one and four and I have drawn the r and this substituent as equatorial because they are they are here axial position. So axial turn into an equatorial positions. So that's the final structure. Next here is to draw the chair and ring flip structure for the following molecule. So here is the chair conformation of these molecules. As you see these, this is their trends to each other. So this is axially up, this is axially down. So this is basically a chair conformation of these molecules. Now I would like to draw the ring-flash chair conformation of these original ring. In order to do that, I want to pull this one down and push this one up that will give me my mirror image of this original ring then I want to Number this carbon one and two then I want to move this one counterclockwise This way then I can see this is turning into carbon number one down carbon This down carbon turning into an off carbon now. I want to put the position So draw the substituents of methyl group two, methyl group one, carbon number one and two. You can see here, if I put it like this, so I put it, but now I have to indicate whether they would be equatorial or axial. I see axial here, axial here. The rule says axial will turn into equatorial. So that means this was axial up, that should be equatorial up. This is axially down. This is equatorial down. The down will remain, stays down. stays up. That's what another thing that you also remember here. So this trans one to diamethyl cyclohexane has two chair confirmations where in one case we have two methyl group on the axial position, another case we see the two methyl group on equatorial positions. We later on will talk about which one which ring would be more stable this one or that one. So when there is one substation on the cyclohexane ring there are there are two chair conformation possible, but those two chair conformation are no longer equivalent or no longer say probably no longer probably will no longer have the same stability. For example, if you look at this cyclics and chair conformation where we have an axial metal group, if you kind of pull this carbon down, push this carbon up, then that will give you the mirror image of that origin ring. And if you want to put that metal group right there that would be in the equatorial position. So you can see here that the metal group here on equatorial up this was initial axial up so upstairs up but axial turn into equatorial so this is the ring-flipped chair conformation of this original ring. Now the question is you have here the metal group on axial position you have here equatorial and metal group on equatorial position. So metal group on axial positions, this chair conformation usually the less stable chair conformation and metal in equatorial positions are more stable chair conformation. And the question is why? Why is axial metal cyclation is less stable compared to the chair conformation where the equatorial where the equatorial metal is on equatorial position? The reason is When you have a substrate in an axial position, there are close approaches from the hydrogens or other substitutes located at the axial positions two carbon away. Usually we call those as one-three dioxide interactions. If you look at this chair conformation, we can see here if you have let's say R is the metal group. So this metal group can see these two hydrogen axial hydrogens pretty close to each other. This is type of straightening interactions. And if you look at the ball stick model, you can see even pretty close, the methyl group hydrogen is very close to these two axial hydrogens. And that interactions again, we know when the atoms are getting too close to each other, they repel each other and they interact with stirring interactions. And because of this stirring interaction, it makes this ring unstable. And how many stirring interactions can you see? This methyl group can interact with one of this hydrogen, this is one axial interactions and here you have another axial interactions we call 1,3-diaxial interactions. So those are kind of two carbons away. You can see it is 1,2-carbon away this hydrogen, axial hydrogen. 1,2 again this is also 2-carbon away axial hydrogen. So this type of steric interaction we call 1,3-diaxial interactions and each repulsions Each of these repulsions is 3.6 kilojoules if R is the methyl group. If R is the methyl group, then it is 3.6 kilojoules. If R is an ethyl group, then it would be around 4.0. If R is a tertiary butyl group, then it would be an even bigger number. It would be 11 point something kilojoules per mole. That means if you have R larger than R group, and if it is on the axial position, the ring will become more and more unstable. So if you look at here in this table, what you can see here, you have the Y group. If Y is fluorine, then the one-dioxal interaction is 0.5. If you have chlorine, it's 1.0, bromine 1.0. If you have methyl group, 3.8 kilojoules or 3.6, sometimes people consider that. If you have an ethyl group, it's a 4.0. So if you have ethyl group again, one di-acetyl interaction is 4.0. If you have tertiary butyl isopropyl group, this is 4.6. So if you have tertiary butyl group, that is 11.4 kilojoules per mole. So if you have a larger and larger substituents here on carbon number one and axial opposition, so then the one-three di-acetyl interactions cost more. energy, cause more strain energy. So here is one of the problems that we are going to calculate how much energy involved. when you are considering 1,2-dioxyl interactions and other type of interactions. So if you look at here 1,2-dimethylcycloxane, we want to count the total strain energy for this C1,2-dimethylcycloxane. Then we'll compare with the C trans 1,2-dimethylcycloxane. And then we will see which one is more stable, right? Which chair conformation would be more stable. So let's first begin with the C1. to dimethylcyclohexane and we want to see how much each of the chair confirmation, the total strain energy, how much total strain energy for each of the chair confirmations. So here we have one to dimethylcyclohexane and this is the chair confirmations of the first chair confirmations. You can see this is metal up and this is equatorial up. So both are up means they are they're seized to each other and then if you just kind of draw the mirror image of these then it will be another chair conformation. This is a ring flip chair conformation. So this metal group this metal group now is turning into an equatorial up and this this was equatorial up. This should be axially up. So again, these are again the ring-flavored chair conformation of this one. If you want to count the total energy involved here, we see one methyl group here. So one methyl group can see two diaxial interactions. There are two carbon aways, so one, two. So one hydrogen is right here, and here's one, two. Another hydrogen is right there. So these two hydrogens would be close to this methyl group. And each of those interactions cost 3.6, a total of 7.3 kilojoules. That's the di-axial interactions. So 2 times 3.6 is around 7.2 kilojoules per mole. We call one-three di-axial interactions. Another type of interactions one can see here, this metal group, this is axially up and this metal group is equatorial up. So when you have axial-equatorial combinations, then they can have a Gauss interactions. Same way here, if you look at this ring flip chair conformation, you can see this metal group is finding axially. This metal group can have one-thread axial interactions, such as one-two. So you can see these hydrogens close right here on this carbon. And on this carbon, there's another hydrogens here. So you can see this metal group will have 7.2 kilojoules. which is coming from one-thread-axial interactions. It also has axial and equatorial metal groups, so there will be a Gauss interaction. So that is 3.6 kilojoules per mole. And in order to look at it, whether they have a Gauss interaction or not, one can draw the Newman projections. If you look at along this axis, you can draw the Newman projections, which would look like this. Where you see this metal group and this metal group, they're 60 degrees apart from each other. So the angle is close to 60 degree. This is the Gauss interactions. When you have a Gauss interaction, this is around 3.6 kilojoules per mole. Same way, if you look at this way, then you will have this metal, this metal 60 degree apart from each other. This is equal to Gauss, to Gauss metal. So this is a Gauss interaction, again, 3.6 kilojoules. So if you calculate the total amount here for this share confirmation, this is 7.3 plus 3.6. which is add up to 10.9 kilojoules. Similarly, if you calculate the total energy involved for this case, we have 7.3 that's the one to the axial interaction, then one gauss interaction, which is 3.6. So total is 10.9 kilojoules. So in this case, these two chair conformations, they have the equal energy. So it means these two will appear 50-50 in the equilibrium mixture. How about for the trend? So trans one to dimethyl case. So this is one of the chair conformation. As you see, this is equatorial down and this is equatorial up. Up and down, this is kind of relating to the trans conformations. So in this case, if you have a ring flip one, if you do that, so this will move on to this side. So that's a equatorial up will turn into axial up. And this is the Equatorial down to turn into Axial down. So this is the second ring, this is this ring flip chair. formation of this one. Now if you count the total strain energy involved for each of these conformation, then you will see here that this is, these two are equatorial, it means there is no one-thread-axial interactions. This is zero kilojoules per mole, that's a zero kilojoule per mole, that's a one-thread-axial interaction because there's no axial. So only thing that you can see here, that these two metal group are in equatorial positions. So those can be considered that those are gaussian metals. So you could have 3.6 kilojoules per mole. In this case, you can see one metal group here, axial positions, one metal group. This, for this metal group, you'll have two this way, one and two, which is 7.3 kilojoules, diac, one, two, diac, and interaction. For this metal group, you can see This down metal, the hydrogen, this down hydrogen, that also gives 7.3 kilojoules. And again, you can look at here, you can see in the Newman projection, these two metal groups are close to each other. These metal groups are anti to each other, so there's no Gauss interaction for this case. So if you count the total amount of energy, the strain energy involved for this ring, so we have zero kilojoules. coming from 1,3-dioxal interactions and 3.6 coming from Gauss interactions, a total of 3.6. And for this chair conformation, we have 14.6 because of this two, the four-dioxal interaction. You can see two for this methyl group, two for this. 14.6 plus zero kilojoules, so no Gauss interactions, a total of 14.6 kilojoules. So we can see here between these two chair conformation, the first chair conformation is most stable chair conformation, which is 3.6 kilojoule. And if you see here, these two metal groups there in equatorial position. So whenever the substitutes are in equatorial position, usually that type of conformations are stable conformations compared to the axial substitutes, all right? Just remember that. So now if you see here, we have the winner here, which is this one. 3.6 kilojoules and if we go back right here for the cis case we have 10.9 for both of them. That means if I say one three dimethyl cyclohexane which chair confirmation would be the stable one then you need to tell you need to show this one would be the most stable one of one three dimethyl cyclohexane. The bottom line is here whenever you are given this type of problem If I say, okay, which one would be, which chair confirmations would be most stable for 1, 2 disubstituted cyclohexane or 1, 3 disubstituted cyclohexanes or 1, 4 disubstituted cyclohexanes. So you first start with the Cs, then you start with the trans, and then you calculate the amount of energy involved, and you should be able to tell which one would be the most stable chair confirmation at the end. So let's Another thing that I would also like to point out here, when to consider that you have Gauss interactions. When you have the two substituents or axial and equatorial positions on the adjacent carbon, remember that. If it is on carbon number one and two on the adjacent carbon, if the substituent is axial and equatorial, you will have Gauss interactions and that is 3.6 kJ per mole. If you have two equatorial positions on, again, on the adjacent carbon, then you will have 3.6 kilojoules per mole. That's the Gauss interactions. If you have two substituent, those are, those are on axial positions. This is axially up and axially down, then there shouldn't be any Gauss interactions. So you won't see a Gauss interactions when you have two substituent adjacent carbons. And there are axial positions. Alright, so now here is in another practice problem. It says below are the two-chair conformations of 1, 2, 4 tri-methyl cyclohexane. Estimate the amount of 1, 3-dioxane strain in each conformer and predict which conformer is most stable. So here is a problem where we would like to calculate the total strain energy for each of the chain chair conformations. So first of all we want to look at The conformer A, we see we have this metal group on carbon number one, which is axial metal group. Carbon number two has a metal group, which is also an axial metal group. and carbon number four which is the methyl group in non-equatorial position. We know when we have one methyl as an axial substituent then it gives two di-axial interactions and each of the di-axial interactions is 3.6 kilojoules. So two times 3.6 kilojoules is around 7.3 kilojoules or 7.2 kilojoules. So here is it should be 7.2. If we have for this methyl group again two times 3.6 this is around 7.3 kilojoules and for carbon number four this is an equatorial position so there shouldn't be any di-axial interaction involved. So total amount of energy 7.3 7.3 plus 0 which is 14.6 kilojoules per mole. Next we want to calculate the total strain energy for this one so if you look at here We see we have carbon number one which is the equatorial, carbon number two which is also an equatorial, so it means there is no di-axial interaction for these two metal groups. But we have carbon number four which is here is the axial position and that is having two times 3.6 kJ per mole and that is 7.3. But if you look at these two, carbon number one and two, those two are adjusting carbon. And those adjacent carbon has two equatorial metal groups. If there is two equatorial metal group on adjacent carbon, then there would be a Gauss interaction, which is 3.6. So 3.6 plus 7.3, that is 10.9. Remember here for the conformer A, we have one and two, this these two metal group on adjacent carbon, but they are on axial positions. When they are on axial position, then there shouldn't be any Gauss interaction. This is why We haven't seen any gauss interaction involved here. So between these two rings, so conformer A has 14.6 kilojoules per mole, conformer B has 10.9 kilojoules per mole. So conformer B is the winner and this would be the most stable ring. Now when you have a dye substitute for cycloalkanes, then if you would like to find out which one, which chair conformation would be the most stable chair conformation, then you should start with the CIS and I substituted compound and draw the chair conformation and ring flip chair conformation of that and then figured out which one would be most stable, then compare with the trans chair conformation and finally should be able to tell which chair conformation will be the winner. So Two dis-dis-substituted cyclohexanes could be like one two dis-substituted cyclohexane, uh hexane, or could be one three dis-substituted cyclohexane. Or could be one four dis-substituted cyclohexane. So let's see. Let's see, uh confirmations of one four dis-substituted cyclohexanes. Which one, which confirmation, shared confirmation of one four dis-substituted cyclohexane would be more stable, the cis one or trans one? If it is cis, which particular cis-Gi confirmation will be most stable. So what we are going to do to solve this type of problems, we will first begin with the cis conformations. So here we can see this is equatorial down and axially down. Both are down, means they are equatorial. They are cis, so this is the cis-dimetal one for cis-1-pore-dimetal cyclohexane. And this is going down, this is going up. it means this is trans one for disubsidated cyclohexane. So now what we're going to do, we're going to compare the conformation for this one and then we're going to compare the ring-flipped conformation with this one and then we'll finally see which one is the winner. So first let's figure it out here. So in this case what we see we have one metal group in equatorial position and this is methyl-griven axial position. This is why we call cis and this is two are opposite. This is why we call trans 1, 2, 1 for dimethyl cyclohexane. Now first we will start with the cis isomers. So cis isomers is this is our original ring as you see here. This methyl-griven equatorial position, this methyl-griven axial positions. If you If you push this one up, pull this one down, then you will have the mirror image of that original ring chair confirmations. And then you can see this is XCLE. down that should be equatorial down and this was initially equatorial down that should turn into axial methyl group down. Now what can you see here? You see here without even calculating you can tell he has one methyl group axial one methyl group equatorial one methyl group axial one methyl group equatorial so the both will have the same amount of energy. All right then if you compare with the trans isomers So here is the chair conformation of the trans. Right here you can see where this two metal group on equitual position and here we have two metal group on axial position. So what we know you can if you want you can calculate the total strain energy for this one. So this one would have would be zero but this one you can see each metal group will have two dioxide interaction which is 7.3. and this one is the 7.3 so total would be 14.3 right and this would be zero so this is most stable chair confirmation so this is zero but if you compare with the cis cis you still have one metal group axial position still have one metal group axial position so it means you will have 7.3 kilojoules per mole that would be the energy strain energy for both of the 7.3, 7.3, but the for trans we have this is zero and this is 14.6. So if I just say which conformations of one for disubstitute or cyclohexane would be most stable, then the answer would be this one because this is this was the clear winner for those among four share confirmations. It has zero energy involved. So this is that take us to our next lecture problem here. This is the practice problem. This is draw the most stable shear conformations of 1-tard-butyl-3-methylcyclohexane. Again, this is a dye substituted cyclohexane and this is 1, 3. So it means you need to start with C's, then you check the trans, and then you compare which one has the highest energy. and which one has the lowest least energy so the least energy will be the winner. If you want you can pause the video and then you can try to answer this question on your own then you can then you can check the answer that I'm going to show you in a second. So first rules as I said we'll start with the C's and it's a one three die substituted case so what you can see here this is we this is where we put the the start B to L curve on equation position and this is a metal group on the equatorial position. Both are equatorial down. It means they are cis. If you do the ring flip, what you can see in the ring flip position, this carbon, this equatorial on, so we move the ring one carbon clockwise these directions. So this is turning into an axially down. It was equatorial down. The equatorial will turn into axial, so axial down. And this was equatorial down. This is turning into L. axial down. So now we can see here, so when you have these two methyl groups in the neutral position, usually there is no di-axial interactions and they are not adjacent to each other, so there is no Gauss interaction, so the energy for this ring will be zero. But for this one, when you have a third neutral group on the axial position, it costs more energy. It is 11.6 or 11.5 kilojoules per mole. for each of the 1,3-dioxyl interactions. So you have two of them. So you have like one with this hydrogen, another with this methyl group, which is much, much more energy. So you have methyl group on axial position, it can also give you 1,3-dioxyl interaction. So this is very light stable ring. So between these two, this is clearly a Wiener case. Now if we consider for the trans one, so for the trans case we can see this is equatorial up and this is metal is axially down. And in this case what we see this is the ring flip one where is the metal tart butyl group turning into axially up and this is turning to metal down. So now we can see here between this two chair conformation the larger group the bulky group charge tertiary butyl gibbonic butyl position and that is a stable ring because then you will have a lace strain energy here. This methyl group is smaller than tart butyl group. So it only give you one two di-axyl interactions, 3.6 kJ per mole. But when you have the tart butyl group on axial position, it gives 11.5 kJ per mole. That's the kind of one-three di-axyl interaction energy. So this ring is going to be less stable. Again, In future, remember when you have a bulky group, always try to put it on an equatorial position because that costs less energy. So between these two rings, what we can see here, so we have a metal group on axial position, so at least you will have 7.3 kJ per mole. This is the Wiener ring. But if you compare with the CIS, we saw here this has zero energy involved because those two are on an equatorial position. So if you compare those four chair conformation, this would be the winner. More stable chair conformation of 1, 3, die, substitute, recycle, Xn. So this is the most stable chair conformation. So that's all for this video.

If the cyclohexane ring appear in chair conformation, there is no torsional strain. So the ring is very stable. The thing is right here, since all this carbon here and also all the carbons here connected by carbon-carbon single bonds, and we know the carbon-carbon single bond, they can freely rotate. And because of the result of simultaneous rotations about all carbon-carbon sigma bond, usually the chair conformation of cycloexons can inter... convert to another chair confirmations by ring flip.

So you can see here if this chair confirmations if they rotated about all carbon-carbon bonds they will take the shape of another chair confirmations shown it on the right. The way that we usually take a look these ones if you just push this carbon this down carbon up and this half carbon down then you will have a ring flip chair confirmation. So this two are the chair confirmations and since this is obtained by ring flipping of this chair confirmations we call ring flip chair confirmations.

Again, usually what we do we can we put we push this down carbon up and then we pull the down carb we pull this carbon down so that's why we get the ring flip chair confirmations. So in this process what actually happened you also can see here well the equatorial bond they turn into an axial bond and axial bond that they turn into an equatorial bonds. So in this process when when there is a ring flip in chair conformation equatorial bonds become axials and axial bonds become equatorial. Now how to draw a ring flip chair conformation. So Usually there are three rules and you must need to remember these three rules in order to write the ring flip chair confirmations.

First is draw the mirror image of your original ring. So this is your chair confirmations. Let's say you have a substituent R on this up carbon and pointing axially. So you have XLR group. So if according to the step one, he says, draw the chair confirm, draw the mirror image of your ring ring.

original ring. So in order to do that, what you have to do is just kind of pull this carbon down and then push this carbon up. That way you will have the ring flip chair confirmations of the original one.

So you know, so when you do that, so we have now the mirror image of your original ring. The second rule you can, you can see here the up carbon they turn into now down carbon and down carbon turn into up carbons in the in the ring flip chair confirmations now step two says on your new ring move every substitute one position clockwise or counterclockwise it doesn't matter which way so if you number these two carbons one and two and now you just kind of on your new ring As it says, move every substituent in one position clockwise or counterclockwise. So we move every substituent by one position this way. So now I have my up carbon turn into a down carbon, and down carbon turn into an up carbon in the new ring. That's what it says here.

Now what we see step three says, draw each substituent on a new position. It was on carbon number one, now it's the carbon number one. If it was equatorial before, then make it axial on the new ring. If it was axial before, then make it equatorial on the new ring.

So we have here the axial, so that means this is going to be equatorial. So axial become equatorial, equatorial become axial, and another thing up. So this is up carbon.

as a half-substituent will remain as a half-substituent. If you have a down, then it will remain as a down, right? So these three steps you need to follow in order to draw the ring flip chair confirmations.

Again, the first is draw the mirror image of your original ring by pulling this carbon down and pushing this carbon up. And then on your new ring move every substituent one position clockwise or counterclockwise. It doesn't matter anyway.

And then Draw each substituent on its new positions on your new ring. And remember, if it was axial, then that will turn into equatorial. If it was equatorial, it will turn into axial. And up stays always up, down stays always down. Now, let's solve a problem together.

So that way you should be able to, you should be able to draw a ring flip-chair conformation. So here is that we want to draw a ring flip chair conformation of these molecules. Again if you like you can pause the video and try to draw the ring flip chair conformation on your own. Then you can check your answer with them.

So I'm going to show you in a second. So first rule is it says I have to draw the mirror image of this original ring. In order to do that What I'm going to do, I'm going to pull this one down and this one up.

That way I'll have my mirror image of this original ring. Now if I number this one, this is one and four, then my new carbon, the carbon number one is with this one and the carbon number four is that one. Usually up carbon turn into down carbon, down carbon turn into an up carbon.

Now I have to have these two substitutes on carbon number one and carbon number four. I don't know what would be the position of those two. However, I can see the rule number, step number three says if it was equatorial here, as you see, if it is axial here, then it will turn into equatorial. If it is axial here, it will turn into equatorial.

So I will have two equatorial. So this substitute in here is going to be equatorial, this substitute is going to be here equatorial. So then I completed my drawing the ring, flip, check, confirmations.

So what I did, if I summarize here, I have the mirror image of this original ring, but I pulled this one down, pushed this one up, so then that way I'll have my new mirror image of the ring. Then I move one, move the substitutes, move the substituents counterclockwise this direction. So I have one and then this is four new position of carbon number one and four and I have drawn the r and this substituent as equatorial because they are they are here axial position. So axial turn into an equatorial positions. So that's the final structure.

Next here is to draw the chair and ring flip structure for the following molecule. So here is the chair conformation of these molecules. As you see these, this is their trends to each other. So this is axially up, this is axially down. So this is basically a chair conformation of these molecules.

Now I would like to draw the ring-flash chair conformation of these original ring. In order to do that, I want to pull this one down and push this one up that will give me my mirror image of this original ring then I want to Number this carbon one and two then I want to move this one counterclockwise This way then I can see this is turning into carbon number one down carbon This down carbon turning into an off carbon now. I want to put the position So draw the substituents of methyl group two, methyl group one, carbon number one and two. You can see here, if I put it like this, so I put it, but now I have to indicate whether they would be equatorial or axial.

I see axial here, axial here. The rule says axial will turn into equatorial. So that means this was axial up, that should be equatorial up. This is axially down.

This is equatorial down. The down will remain, stays down. stays up.

That's what another thing that you also remember here. So this trans one to diamethyl cyclohexane has two chair confirmations where in one case we have two methyl group on the axial position, another case we see the two methyl group on equatorial positions. We later on will talk about which one which ring would be more stable this one or that one. So when there is one substation on the cyclohexane ring there are there are two chair conformation possible, but those two chair conformation are no longer equivalent or no longer say probably no longer probably will no longer have the same stability.

For example, if you look at this cyclics and chair conformation where we have an axial metal group, if you kind of pull this carbon down, push this carbon up, then that will give you the mirror image of that origin ring. And if you want to put that metal group right there that would be in the equatorial position. So you can see here that the metal group here on equatorial up this was initial axial up so upstairs up but axial turn into equatorial so this is the ring-flipped chair conformation of this original ring. Now the question is you have here the metal group on axial position you have here equatorial and metal group on equatorial position.

So metal group on axial positions, this chair conformation usually the less stable chair conformation and metal in equatorial positions are more stable chair conformation. And the question is why? Why is axial metal cyclation is less stable compared to the chair conformation where the equatorial where the equatorial metal is on equatorial position?

The reason is When you have a substrate in an axial position, there are close approaches from the hydrogens or other substitutes located at the axial positions two carbon away. Usually we call those as one-three dioxide interactions. If you look at this chair conformation, we can see here if you have let's say R is the metal group. So this metal group can see these two hydrogen axial hydrogens pretty close to each other.

This is type of straightening interactions. And if you look at the ball stick model, you can see even pretty close, the methyl group hydrogen is very close to these two axial hydrogens. And that interactions again, we know when the atoms are getting too close to each other, they repel each other and they interact with stirring interactions. And because of this stirring interaction, it makes this ring unstable.

And how many stirring interactions can you see? This methyl group can interact with one of this hydrogen, this is one axial interactions and here you have another axial interactions we call 1,3-diaxial interactions. So those are kind of two carbons away.

You can see it is 1,2-carbon away this hydrogen, axial hydrogen. 1,2 again this is also 2-carbon away axial hydrogen. So this type of steric interaction we call 1,3-diaxial interactions and each repulsions Each of these repulsions is 3.6 kilojoules if R is the methyl group. If R is the methyl group, then it is 3.6 kilojoules. If R is an ethyl group, then it would be around 4.0.

If R is a tertiary butyl group, then it would be an even bigger number. It would be 11 point something kilojoules per mole. That means if you have R larger than R group, and if it is on the axial position, the ring will become more and more unstable. So if you look at here in this table, what you can see here, you have the Y group.

If Y is fluorine, then the one-dioxal interaction is 0.5. If you have chlorine, it's 1.0, bromine 1.0. If you have methyl group, 3.8 kilojoules or 3.6, sometimes people consider that. If you have an ethyl group, it's a 4.0.

So if you have ethyl group again, one di-acetyl interaction is 4.0. If you have tertiary butyl isopropyl group, this is 4.6. So if you have tertiary butyl group, that is 11.4 kilojoules per mole. So if you have a larger and larger substituents here on carbon number one and axial opposition, so then the one-three di-acetyl interactions cost more. energy, cause more strain energy.

So here is one of the problems that we are going to calculate how much energy involved. when you are considering 1,2-dioxyl interactions and other type of interactions. So if you look at here 1,2-dimethylcycloxane, we want to count the total strain energy for this C1,2-dimethylcycloxane.

Then we'll compare with the C trans 1,2-dimethylcycloxane. And then we will see which one is more stable, right? Which chair conformation would be more stable.

So let's first begin with the C1. to dimethylcyclohexane and we want to see how much each of the chair confirmation, the total strain energy, how much total strain energy for each of the chair confirmations. So here we have one to dimethylcyclohexane and this is the chair confirmations of the first chair confirmations. You can see this is metal up and this is equatorial up. So both are up means they are they're seized to each other and then if you just kind of draw the mirror image of these then it will be another chair conformation.

This is a ring flip chair conformation. So this metal group this metal group now is turning into an equatorial up and this this was equatorial up. This should be axially up.

So again, these are again the ring-flavored chair conformation of this one. If you want to count the total energy involved here, we see one methyl group here. So one methyl group can see two diaxial interactions. There are two carbon aways, so one, two.

So one hydrogen is right here, and here's one, two. Another hydrogen is right there. So these two hydrogens would be close to this methyl group. And each of those interactions cost 3.6, a total of 7.3 kilojoules. That's the di-axial interactions.

So 2 times 3.6 is around 7.2 kilojoules per mole. We call one-three di-axial interactions. Another type of interactions one can see here, this metal group, this is axially up and this metal group is equatorial up.

So when you have axial-equatorial combinations, then they can have a Gauss interactions. Same way here, if you look at this ring flip chair conformation, you can see this metal group is finding axially. This metal group can have one-thread axial interactions, such as one-two. So you can see these hydrogens close right here on this carbon.

And on this carbon, there's another hydrogens here. So you can see this metal group will have 7.2 kilojoules. which is coming from one-thread-axial interactions.

It also has axial and equatorial metal groups, so there will be a Gauss interaction. So that is 3.6 kilojoules per mole. And in order to look at it, whether they have a Gauss interaction or not, one can draw the Newman projections. If you look at along this axis, you can draw the Newman projections, which would look like this. Where you see this metal group and this metal group, they're 60 degrees apart from each other.

So the angle is close to 60 degree. This is the Gauss interactions. When you have a Gauss interaction, this is around 3.6 kilojoules per mole. Same way, if you look at this way, then you will have this metal, this metal 60 degree apart from each other. This is equal to Gauss, to Gauss metal.

So this is a Gauss interaction, again, 3.6 kilojoules. So if you calculate the total amount here for this share confirmation, this is 7.3 plus 3.6. which is add up to 10.9 kilojoules. Similarly, if you calculate the total energy involved for this case, we have 7.3 that's the one to the axial interaction, then one gauss interaction, which is 3.6. So total is 10.9 kilojoules.

So in this case, these two chair conformations, they have the equal energy. So it means these two will appear 50-50 in the equilibrium mixture. How about for the trend?

So trans one to dimethyl case. So this is one of the chair conformation. As you see, this is equatorial down and this is equatorial up. Up and down, this is kind of relating to the trans conformations. So in this case, if you have a ring flip one, if you do that, so this will move on to this side.

So that's a equatorial up will turn into axial up. And this is the Equatorial down to turn into Axial down. So this is the second ring, this is this ring flip chair. formation of this one.

Now if you count the total strain energy involved for each of these conformation, then you will see here that this is, these two are equatorial, it means there is no one-thread-axial interactions. This is zero kilojoules per mole, that's a zero kilojoule per mole, that's a one-thread-axial interaction because there's no axial. So only thing that you can see here, that these two metal group are in equatorial positions. So those can be considered that those are gaussian metals.

So you could have 3.6 kilojoules per mole. In this case, you can see one metal group here, axial positions, one metal group. This, for this metal group, you'll have two this way, one and two, which is 7.3 kilojoules, diac, one, two, diac, and interaction.

For this metal group, you can see This down metal, the hydrogen, this down hydrogen, that also gives 7.3 kilojoules. And again, you can look at here, you can see in the Newman projection, these two metal groups are close to each other. These metal groups are anti to each other, so there's no Gauss interaction for this case. So if you count the total amount of energy, the strain energy involved for this ring, so we have zero kilojoules. coming from 1,3-dioxal interactions and 3.6 coming from Gauss interactions, a total of 3.6.

And for this chair conformation, we have 14.6 because of this two, the four-dioxal interaction. You can see two for this methyl group, two for this. 14.6 plus zero kilojoules, so no Gauss interactions, a total of 14.6 kilojoules.

So we can see here between these two chair conformation, the first chair conformation is most stable chair conformation, which is 3.6 kilojoule. And if you see here, these two metal groups there in equatorial position. So whenever the substitutes are in equatorial position, usually that type of conformations are stable conformations compared to the axial substitutes, all right? Just remember that. So now if you see here, we have the winner here, which is this one.

3.6 kilojoules and if we go back right here for the cis case we have 10.9 for both of them. That means if I say one three dimethyl cyclohexane which chair confirmation would be the stable one then you need to tell you need to show this one would be the most stable one of one three dimethyl cyclohexane. The bottom line is here whenever you are given this type of problem If I say, okay, which one would be, which chair confirmations would be most stable for 1, 2 disubstituted cyclohexane or 1, 3 disubstituted cyclohexanes or 1, 4 disubstituted cyclohexanes. So you first start with the Cs, then you start with the trans, and then you calculate the amount of energy involved, and you should be able to tell which one would be the most stable chair confirmation at the end.

So let's Another thing that I would also like to point out here, when to consider that you have Gauss interactions. When you have the two substituents or axial and equatorial positions on the adjacent carbon, remember that. If it is on carbon number one and two on the adjacent carbon, if the substituent is axial and equatorial, you will have Gauss interactions and that is 3.6 kJ per mole.

If you have two equatorial positions on, again, on the adjacent carbon, then you will have 3.6 kilojoules per mole. That's the Gauss interactions. If you have two substituent, those are, those are on axial positions.

This is axially up and axially down, then there shouldn't be any Gauss interactions. So you won't see a Gauss interactions when you have two substituent adjacent carbons. And there are axial positions.

Alright, so now here is in another practice problem. It says below are the two-chair conformations of 1, 2, 4 tri-methyl cyclohexane. Estimate the amount of 1, 3-dioxane strain in each conformer and predict which conformer is most stable. So here is a problem where we would like to calculate the total strain energy for each of the chain chair conformations.

So first of all we want to look at The conformer A, we see we have this metal group on carbon number one, which is axial metal group. Carbon number two has a metal group, which is also an axial metal group. and carbon number four which is the methyl group in non-equatorial position. We know when we have one methyl as an axial substituent then it gives two di-axial interactions and each of the di-axial interactions is 3.6 kilojoules. So two times 3.6 kilojoules is around 7.3 kilojoules or 7.2 kilojoules.

So here is it should be 7.2. If we have for this methyl group again two times 3.6 this is around 7.3 kilojoules and for carbon number four this is an equatorial position so there shouldn't be any di-axial interaction involved. So total amount of energy 7.3 7.3 plus 0 which is 14.6 kilojoules per mole. Next we want to calculate the total strain energy for this one so if you look at here We see we have carbon number one which is the equatorial, carbon number two which is also an equatorial, so it means there is no di-axial interaction for these two metal groups. But we have carbon number four which is here is the axial position and that is having two times 3.6 kJ per mole and that is 7.3.

But if you look at these two, carbon number one and two, those two are adjusting carbon. And those adjacent carbon has two equatorial metal groups. If there is two equatorial metal group on adjacent carbon, then there would be a Gauss interaction, which is 3.6. So 3.6 plus 7.3, that is 10.9.

Remember here for the conformer A, we have one and two, this these two metal group on adjacent carbon, but they are on axial positions. When they are on axial position, then there shouldn't be any Gauss interaction. This is why We haven't seen any gauss interaction involved here. So between these two rings, so conformer A has 14.6 kilojoules per mole, conformer B has 10.9 kilojoules per mole.

So conformer B is the winner and this would be the most stable ring. Now when you have a dye substitute for cycloalkanes, then if you would like to find out which one, which chair conformation would be the most stable chair conformation, then you should start with the CIS and I substituted compound and draw the chair conformation and ring flip chair conformation of that and then figured out which one would be most stable, then compare with the trans chair conformation and finally should be able to tell which chair conformation will be the winner. So Two dis-dis-substituted cyclohexanes could be like one two dis-substituted cyclohexane, uh hexane, or could be one three dis-substituted cyclohexane. Or could be one four dis-substituted cyclohexane. So let's see.

Let's see, uh confirmations of one four dis-substituted cyclohexanes. Which one, which confirmation, shared confirmation of one four dis-substituted cyclohexane would be more stable, the cis one or trans one? If it is cis, which particular cis-Gi confirmation will be most stable. So what we are going to do to solve this type of problems, we will first begin with the cis conformations. So here we can see this is equatorial down and axially down.

Both are down, means they are equatorial. They are cis, so this is the cis-dimetal one for cis-1-pore-dimetal cyclohexane. And this is going down, this is going up. it means this is trans one for disubsidated cyclohexane.

So now what we're going to do, we're going to compare the conformation for this one and then we're going to compare the ring-flipped conformation with this one and then we'll finally see which one is the winner. So first let's figure it out here. So in this case what we see we have one metal group in equatorial position and this is methyl-griven axial position.

This is why we call cis and this is two are opposite. This is why we call trans 1, 2, 1 for dimethyl cyclohexane. Now first we will start with the cis isomers. So cis isomers is this is our original ring as you see here.

This methyl-griven equatorial position, this methyl-griven axial positions. If you If you push this one up, pull this one down, then you will have the mirror image of that original ring chair confirmations. And then you can see this is XCLE. down that should be equatorial down and this was initially equatorial down that should turn into axial methyl group down.

Now what can you see here? You see here without even calculating you can tell he has one methyl group axial one methyl group equatorial one methyl group axial one methyl group equatorial so the both will have the same amount of energy. All right then if you compare with the trans isomers So here is the chair conformation of the trans. Right here you can see where this two metal group on equitual position and here we have two metal group on axial position. So what we know you can if you want you can calculate the total strain energy for this one.

So this one would have would be zero but this one you can see each metal group will have two dioxide interaction which is 7.3. and this one is the 7.3 so total would be 14.3 right and this would be zero so this is most stable chair confirmation so this is zero but if you compare with the cis cis you still have one metal group axial position still have one metal group axial position so it means you will have 7.3 kilojoules per mole that would be the energy strain energy for both of the 7.3, 7.3, but the for trans we have this is zero and this is 14.6. So if I just say which conformations of one for disubstitute or cyclohexane would be most stable, then the answer would be this one because this is this was the clear winner for those among four share confirmations.

It has zero energy involved. So this is that take us to our next lecture problem here. This is the practice problem.

This is draw the most stable shear conformations of 1-tard-butyl-3-methylcyclohexane. Again, this is a dye substituted cyclohexane and this is 1, 3. So it means you need to start with C's, then you check the trans, and then you compare which one has the highest energy. and which one has the lowest least energy so the least energy will be the winner.

If you want you can pause the video and then you can try to answer this question on your own then you can then you can check the answer that I'm going to show you in a second. So first rules as I said we'll start with the C's and it's a one three die substituted case so what you can see here this is we this is where we put the the start B to L curve on equation position and this is a metal group on the equatorial position. Both are equatorial down. It means they are cis. If you do the ring flip, what you can see in the ring flip position, this carbon, this equatorial on, so we move the ring one carbon clockwise these directions.

So this is turning into an axially down. It was equatorial down. The equatorial will turn into axial, so axial down.

And this was equatorial down. This is turning into L. axial down.

So now we can see here, so when you have these two methyl groups in the neutral position, usually there is no di-axial interactions and they are not adjacent to each other, so there is no Gauss interaction, so the energy for this ring will be zero. But for this one, when you have a third neutral group on the axial position, it costs more energy. It is 11.6 or 11.5 kilojoules per mole. for each of the 1,3-dioxyl interactions. So you have two of them.

So you have like one with this hydrogen, another with this methyl group, which is much, much more energy. So you have methyl group on axial position, it can also give you 1,3-dioxyl interaction. So this is very light stable ring.

So between these two, this is clearly a Wiener case. Now if we consider for the trans one, so for the trans case we can see this is equatorial up and this is metal is axially down. And in this case what we see this is the ring flip one where is the metal tart butyl group turning into axially up and this is turning to metal down.

So now we can see here between this two chair conformation the larger group the bulky group charge tertiary butyl gibbonic butyl position and that is a stable ring because then you will have a lace strain energy here. This methyl group is smaller than tart butyl group. So it only give you one two di-axyl interactions, 3.6 kJ per mole. But when you have the tart butyl group on axial position, it gives 11.5 kJ per mole. That's the kind of one-three di-axyl interaction energy.

So this ring is going to be less stable. Again, In future, remember when you have a bulky group, always try to put it on an equatorial position because that costs less energy. So between these two rings, what we can see here, so we have a metal group on axial position, so at least you will have 7.3 kJ per mole.

This is the Wiener ring. But if you compare with the CIS, we saw here this has zero energy involved because those two are on an equatorial position. So if you compare those four chair conformation, this would be the winner.

More stable chair conformation of 1, 3, die, substitute, recycle, Xn. So this is the most stable chair conformation. So that's all for this video.

Transcript for:Understanding Cyclohexane Conformations

Transcript for:
Understanding Cyclohexane Conformations