Draw the two chair conformations of each compound, and label t...

Question

Draw the two chair conformations of each compound, and label the substituents as axial and equatorial. In each case, determine which conformation is more stable.

a. cis-1-ethyl-2-isopropylcyclohexane

b. trans-1-ethyl-2-isopropylcyclohexane

Accepted Answer

Hey everyone, Let's solve this problem. It says to die substituted cycle Texans are given below draw the two chair confirmations for each of them and label the more stable confirmation. So how do we know which chair is more stable? The more stable chair confirmation will have the bulkier groups in the equatorial position. Okay, so that's what we're going to look for. And another important thing to remember is that when we do the chair flip groups in the axial position will then be in the equatorial position and vice versa groups that were in the equatorial position after a chair flip will be in the actual position. And to solve this problem, I like to use the following steps first I draw the two D structure. So the flat structure using the wedges, which I also will call the up position. You'll see why in a dash which will be the down position. And you also want to number that ring right then we will draw the chair and number the chair accordingly. Then we'll add the respective substitue ints to the correct carbon numbers in their correct position, in their axial or equatorial. And when we repeat these steps for the next chair, it's important to number the chair correctly. So we're going to number the other chair in the same spots. So you want the same carbon to have the same numbers. Right? So I'll demonstrate all of this with our compounds we have here. So we'll start off with a cyst one, TERT bugle two methyl cyclo hexi. So I see my bases cyclo hexane. So let's draw The six member ring and we'll number it. I like to start at the top like a clock and go clockwise 123456. Then at carbon number one we have tart beautiful. Which is going to be one carbon and three methyl groups attached to that carbon. And since we have sis, I'm going to make both of our groups wedge. Why not in on carbon number two we have a metal hoops should be also wedge, right sis is the same side. So these will both be up in this case since I drew them as a witch. Okay, let's draw the chairs. So we have our first chair and we're going to number it. I like to start with the left most corner always And Go Clockwise one through 6. So it's important to remember that the actual groups follow the direction of the corner. So what I mean by that is corner number one for example, looks like it's pointing downwards. So there are two groups you could go axial or equatorial and the actual group is going to be down since the corner is down. Don't forget we have hydrogen is here. So those will be dashed or down. So on carbon number one the corner is going down. So are hydrogen or our down group is going to be axial where our TERT bugle group is going to be up or equatorial CCH 3 3. Does that make sense. And now carbon # two, the corner is pointing up. So our methyl group will be in the axial position because it is up and the hydrogen will be down in the equatorial position. Okay, so let's flip the chair or rotate around the single bond. Mhm. So now that left most corner is going to be up and we'll again wanna start numbering in the same spot. So I numbered that left most corner as one in my first chair. So the second chair has to be Number one in the same spot. So now my corner is up. So my group that is up which is the little group is going to be axial this time and the hydrogen will be equatorial down. And carbon number to that corner is down. So my hydrogen that is down is going to be acsi Oh and my muscle group is going to be equatorial pointing up. So in the first structure, my Bureau group is equatorial In the second group, my method group is equatorial. And in the first chair my Method group is axial and The 2nd Chair, my bugle group is axial. So again, we're seeing those groups are switching their confirmation. Right, so which one is more stable? Well, we said that the bulky group wants to be in the equatorial position. Which group is more bulky TERT bugle or a methyl group definitely the TERT bugle. Right, so that is going to make our first chair confirmation more stable because that tribunal group is equatorial here. Okay, I hope that makes sense. Let's do this with the next structure. So we have trans one to dye bromo cyclo hexane. So again we're starting with cyclo hexane, a six member ring and we have one to dye bromo and this time it's trans, so one of them will be wedged and one will be dash. Let's number our carbons clockwise, one through six and we'll make number one bro mean wedge and romi non carbon two will make dashed. So this one on carbon number one is up, The Brahmin on Carbon # two is down. So let's translate this to our chair confirmation. No, that is not pretty enough for you guys. So we have our first chair numbering one through six. I again like to start from the left most carbon just to keep it all the same every time I do it. So carbon number one, my bruning group is up but my corner is down so the hydrogen will be the group that is going axial while the booming is up in the equatorial position. And on carbon number two which is up the corner is up so my brewing group is down so the hydrogen will be axial and the bruning will be equatorial down. Okay, next chair. And again numbering that chair in the same spot, starting with the left most corner going clockwise. So corner number one carbon number one. My bro mean group is up, my corner is up, so bromine will be axial. This time hydrogen will be equatorial down carbon number two. My broom in group is down. My corner is down, so my domain will be axial. Well, let me draw a little dash going down there and my hydrogen will be up equatorial. Okay, so in the first structure, both bro means are equatorial. In the second structure, both bro means our axial, so which one is going to be more stable? Definitely the first structure, Right? Both of those bulkier bro means are in the equatorial position there. Okay, that's it for this problem. I hope this video is helpful and thanks for watching.

Draw the two chair conformations of each compound, and label the substituents as axial and equatorial. In each case, determine which conformation is more stable.
a. cis-1-ethyl-2-isopropylcyclohexane
b. trans-1-ethyl-2-isopropylcyclohexane

Key Concepts

Chair Conformation

Axial and Equatorial Positions

Cis and Trans Isomerism

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