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Video transcript

today we'll be talking about how to separate enantiomers from each other enantiomers are like your left and right hands there are mirror images of each other but they look almost identical remember that much like we use right and left to describe which hand is which scientists use the letters s and R to designate which enantiomer is which when you only have one chiral Center however when you have multiple chiral centers there are other ways of designating enantiomers but we won't be getting into that today because that's much more complicated here we have a set of enantiomers this is the S conformation of the little mine and here on the right is our conformation why does it matter that we have two different confirmations well you can see the difference quite clearly at the chiral Center where one of the groups points into the screen and the other points out of the screen and just because of the simple change in conformation the S version was found to lead to terrible birth defects when consumed by mothers and because of this drug companies now try to make sure that the active ingredient in their drug is only one particular enantiomer so how would we go about separating these two one technique that you could use is chiral column chromatography you would need a stationary phase that is chiral meaning something that will only bind either to the r confirmation or the s confirmation of your desired enantiomer so how does the chiral stationary phase only bind to one of the enantiomers picture the two enantiomers as your right and left hand if your right hand tries to shake another person's right hand it seems normal right the two fit together properly but if your right hand tries to shake your own left hand it doesn't seem like they line up quite right that's the exact same thing that happens with the chiral stationary face and the wrong enantiomer next what you do is you'd load that mixture of enantiomers so on top here you might see that you have some kind of ban of your mixture this is racemic meaning that it has a 50/50 mixture of enantiomers so that's what you're seeing here in the yellow if we take a closer look you'll see that this has some of the S conformation and some of the are conformation - thrown in and as this moves through the stationary phase so once you open up the stopcock what you'll see is that if the R enantiomer was the one that binds tightly to the stationary phase it won't move very quickly but with the S enantiomer it might be racing through since it's not really interacting that much with the stationary phase and for first to interact with the mobile phase once you've collected all of the s enantiomers in your flask all you'll have left in the column is the RN antemer which is pretty tightly bound to the chiral stationary phase next what you do is when you have this column you'd want to pour in lots of solvent so that you can get the RN antemer to come out because as this pushes down through the column it will take the R enantiomer with it giving you just the r enantiomer in your flask and there you've done a successful chiral resolution the same principle can also be applied to gas chromatography let's quickly review how gas chromatography works you insert your sample in here a gas flows through and then it goes into this long tube that contains the stationary phase and mobile phase and goes to the detector and if we were to zoom in on this and dry that's just kind of a long tube again what you'd see is that if this time the stationary phase was attracted to the S enantiomer instead you'd see that the S enantiomer is kind of sticking to the sides sticking to the stationary phase while the RN antemer races through with the mobile phase so there are actually a number of other ways you can separate out enantiomers but those tend to be much more complicated these are just two of the common ways you can do it and in both of them whether you're doing column chromatography with a solid stationary phase or a gas chromatography with a liquid stationary phase the important thing to remember is that your stationary phase should be chiral and bind to the enantiomer that you want