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Enantiomers and diastereomers

Video transcript

we've already spent a lot of time talking about enantiomers these are stereoisomers that are non-superimposable mirror images of each other and they have opposite configurations at all chirality centers diastereomers are also stereo isomers but these are stereoisomers that are non-superimposable non mirror images of each other so these are stereoisomers that are not enantiomers and diastereomers have opposite configurations at some chirality centers if we look at this compound up here we have a cyclopropane ring with a bromine coming off and the chlorine coming off we know from earlier videos that there are two chirality centers so this carbon is a chiral Center and so is this one the total number of stereo isomers is two to the N where n is equal to the number of chiral centers and since n is equal to two for this drawing we would expect to be able to draw two to the second power or for stereo isomers so there should be a total of four stereo isomers actually two to the N is just a maximum and we'll talk about that in later videos so let's draw let's draw all forward stereo isomers and let's look at the relationship between them let's think about how to draw our four stereo isomers for the first one we could have both halogens coming out at us in space so I put the bromine on a wedge and I put the chlorine on a wedge next we could have both halogens going away from us in space so I put the bromine on a dash and same with the chlorine next for a third serialize summer we can have one halogen coming out at us so I'll make that the bromine and one going away from us and for the last one we could just reverse it we can have the bromine going away from us and the chlorine coming out at us next let's look at the relationships between our stereo isomers and let's start with the relationship between stereo isomer 1 and stereo isomer 2 model sets really help in stereochemistry so we're going to look at videos for a lot of these let's go look at the video comparing stereo isomer 1 and stereo isomer two on the Left we have stereoisomer one both halogens are coming out at us in space on the right is stereoisomer 2 we're both halogens are going away from us in space if I hold these two stereoisomers next to each other and I rotate the one on the right we can see they're actually mirror images of each other and there are non-superimposable mirror images if I line up the chlorines then the bromine czar not in the right position and if I try to line up the bro means now the chlorines are not in the right position so these are non-superimposable mirror images of each other these are enantiomers so we saw in the video that one in two are enantiomers of each other they are non-superimposable mirror images and they have opposite configurations at all chirality centers and that's easy to see if you look at the drawings here so at this carbon we have bromine on a wedge and if we change it to a dash right we see we have this one on the right we look at this chiral Center we have chlorine on a wedge and here it's changed to a dash so that's an opposite configuration at both chiral centers and so that's how we know that's one way of knowing that this one on the right is the mirror image of the one on the left they are enantiomers let's look at the relationship between stereoisomers 3 & 4 on the left is stereoisomer 3 with bromine up and chlorine down on the right is 4 with bromine down and chlorine up if we hold them together and I rotate the one on the right it's easy to see that these are mirror images of each other and they are non-superimposable if I put the chlorines on top of each other now the bromine is don't line up and if I try to line up the bromine Zin the chlorines don't so these are non-superimposable mirror images of each other these are enantiomers so 3 & 4 are enantiomers of each other they are non-superimposable mirror images and they have opposite configurations at all chirality centers so at this chiral center we have bro on a wedge and over here we have bromine on a dash at this chiral Center we have chlorine on a dash and over here we have it on a wedge so we have opposite configurations at both chirality centers next let's compare stereoisomers 2 & 3 so what's the relationship between a 2 & 3 on the left is stereoisomer 2 with the bromine and the chlorine going away from us in space on the right is 3 with bromine up and chlorine down if I hold the two stereoisomers next to each other and I rotate the one on the right we can see these are not mirror images of each other the bro means look right but the chlorines don't one chlorine is up and one Klein is down if I try to superimpose these I can get the bro means to match but not the chlorines and if I try to make the chlorines line up then the bro means won't so these are non super imposable non mirror images these are diastereomers we saw in the video that 2 & 3 are non super imposable and they're also non mirror images therefore they are diastereomers let me write that down here so 2 & 3 represent a pair of diastereomers and diastereomers have opposite configurations at some chirality centers so if we look at this carbon we have bromine on a dash and over here we have bromine on a wedge so that's opposite but if we look at this one we have chlorine on a dash and over here we have chlorine on a dash so that's the same so we only have an opposite configuration at one chiral center and so these are diastereomers what about comparing two stereo isomer to with stereo isomer for so let's look at the video for that on the left is stereo isomer - with the bromine and chlorine going away from us on the right is 4 with bromine down and chlorine up so we hold the two stereo isomers next to each other and we rotate the one on the right and we can see these are not mirror images the chlorines look right but the bro means don't one means down and one bromine is up if we try to superimpose one on top of the other the chlorines line up but not the bro means that if I try of matching the bro means now the chlorines don't so these are non super imposable non mirror images these are diastereomers so 2 & 4 are diastereomers they are non super imposable non mirror images of each other and they only have opposite configurations at some chirality centers in this case 1 so if we look at this chiral center the bromine is on a dash and we look at this one the bromine is also on a dash so that's the same if we look at this one the chlorine is on a dash and over here the chlorines on a wedge so that's an opposite configuration at only one chiral center so 2 & 4 are diastereomers what about comparing 1 & 3 so thinking about 1 & 3 so we don't need a video for this anymore I think we've got the hang of it if we look at this carbon we have bromine on a wedge and at this carbon we have bromine on a wedge so that's the same at this carbon we have chlorine on a wedge and at this one we have chlorine on a dash so that's different so we only have an opposite configuration at one chirality Center so 1 & 3 are diastereomers of each other and the same thing if you're thinking about 1 & 4 those would also be diastereomers of each other