Complete the structure of each of these so that it matches the...

Question

Complete the structure of each of these so that it matches the (R) or (S) configuration associated with the name.

(e)

Accepted Answer

Welcome back everybody. Our next problem says in the compound below, correct its structure so that it matches the configuration R or S in its name. And we have this cyclohexane ring with an oxygen or excuse me, with alcohol on one carbon and on the adjacent carbon to that, a chlorine and a methyl group. So let's look at its name. Its name is in parentheses. One S two R, then two chloro two methyl cyclohexane, one all and then we have four, multiple choice answer possibilities with different arrangements using solid wedges and dashed wedges to show the geometry around those carbons with the substituents. So we'll go into more detail about those as we look at our molecule here. So we're given the configuration of the name. So the key we want to focus in on here is this one S two R which tells us the geometry around each of the chiral centers. So we know it's on carbon one and from our name one, all carbon one is the one with the alcohol and then carbon two, it's two R and carbon two is the one with the methyl group and the chloride. So we've got carbon one and carbon two. Yeah. And I'm putting those numbers not within the ring as we usually do, but out of it because we'll need our room to figure out our R and our S configuration. So we're given a molecule without any geometry, it's just given solid or just lines showing where the substituents are. And we need to convert those to the solid wedges indicating something coming out of the plane of the screen towards us or dash wedges, something going back out of the plane behind us, not behind us. Yeah, if the screen were facing us, so let's look at our first group, the alcohol group. And what we'd want to do is recall that if the lowest priority group is in the back. So if we number our groups around our chiral carbon from 1 to 4 highest to lowest priority, the lowest is in the back and then to go from groups 1 to 3, if that goes in a clockwise direction, that's an R arrangement. And then I wrote CCW counterclockwise, that's an s arrangement. Then the other way around if the lowest party group is in the front and the other groups are in a clockwise arrangement, that's a counterclockwise arrangement, that's R. And the way to remember that is if you think of putting the lowest party group in the back, so least important to the back of the line is sort of the default position. And in that position. If you turn right, you're turning clockwise. If you turn left or s for sinister, you are going counterclockwise. Whereas if we reverse the order of things and put the lowest priority group up in the front, so everything's turned around everything topsy turvy, then if you're going clockwise or right, it's labeled, s so it's like it's opposite day. That's how I kind of think of it. So let's look at our carbon one where our alcohol group is and put our priority groups. Now there's no story chemistry indicated here. I don't know what's in the back. So what I need to do is label groups 12 and three. Do they go clockwise? Do they go counterclockwise and compare it to my known s arrangement? So our top priority group here, number one is the alcohol group. So that's number one. And then we have two bonds to carbons here. We have no other bond indicated. Meaning there's a hydrogen as our fourth, that's clearly lowest priority. So on one side, our carbon goes to another carbon, on the other side, our carbon goes to a chlorine. So the side going to carbon two is higher priority. So we'll put a number two by that bond to carbon two and then a number three by that bond two carbon six, what direction these go in? I have to go clockwise. So that means if I go clockwise, if I'm in my default position, lowest in the back. That would be the R arrangement. But I have the s arrangement. So I'm going for carbon one, going clockwise. But oops, I've wrote R, I'm going clockwise but I'm s that means I'm an opposite day. I'm in topsy turvy world. So my lowest priority group, my hydrogen must be in the front. So write H in front. Now, in carbon two, let's label our groups one through three. Now, this one's a little bit trickier. There's no hydrogen on this carbon. It has three bonds to other carbons and one bond to a chlorine. What's our lowest priority group? Well, it's going to be one of the carbons. We know that chlorine will be number one, I labeled the other party groups in red. I'm gonna label these in green because we're gonna start getting a little cluttered here with two adjacent carbons party group. One is chlorine. That's pretty obvious. So now with my carbons, but two carbons in the ring and one methyl group, the methyl group is going to be the lowest because there's only bonds to other hydrogens there. So we're gonna ignore that. Then we have to figure out two and three. Well, we've got a carbon on carbon three that just says going around the ring. Then I've got that carbon on carbon one that has an alcohol. So priority two will be that bond two carbon one and then priority three will be the bond two carbon three. So now to go from 1 to 2 to 3 ami going clockwise or counterclockwise. I'm going counterclockwise in this case. So now for carbon two, I'm going counter clockwise. All right. CCW. And from the name, I know I have the R geometry. So once again, I'm in opposite world with this one. And so my lowest priority group in this case, not hydrogen but methyl. My ch three must be in the front, least important in the front, opposite day. So now I just have to find the multiple choice option that conforms to these two conditions. So for carbon one, the hydrogen has to be in the front. That means my other substituent oh must be in the back. So I'll put oh in back. And then for number two where the methyl group has to be in the front. That means that chlorine must be in the back. So here we go. Let's look at choice. A this one shows oh on a dashed wedge in the back. So that's correct. And then it shows chlorine on a dash wedge in the back metal in the front. So right away on choice A, we have the correct arrangement. It matches the given name. But let's just briefly look at our other answer choices just to be really thorough here and choice B are ohs in the back. That's correct. But on the other carbon, the chlorine is in the front and the metal groups in the back. So choice B incorrect. In choice C, the alcohol group is in the front. So that's incorrect. And then the chlorine groups in the front and the methyl groups in the back. So incorrect of both chiral centers and then in choice D, the alcohol groups in the front. So that's incorrect. Although the chlorine is in the back and the methyl is in the front. So that's correct. But choice D is incorrect at the carbon one Carol center. So once again to draw the structure so that it matches the configuration in its name. The answer is choice A for carbon one to be in the S geometry, which needs to be in the back for carbon two to be in the R geometry. Chlorine must be in the back and metal in the front. See you in the next video.

Complete the structure of each of these so that it matches the (R) or (S) configuration associated with the name.
(e)

Key Concepts

Stereochemistry

Chirality

Nomenclature of Organic Compounds

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