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Current time:0:00Total duration:11:02

Video transcript

in the last video we learned a little bit about what a chiral molecule or what a chiral carbon or a chiral atom is what I want to do in this video is go through a bunch of examples and see if we can identify if there are any chiral atoms and to also see if we're dealing with a chiral molecule so let's go look at our examples here so here I have what is this this is chloro cyclo pentene so the first question is do we have any do we have any chiral atoms and when we look at our definition that we thought of chiral atoms it all comes from this notion of handedness and not being able to be superimposable on your mirror image but we said that they're usually carbons bonded to four different groups so let's see it do we have any carbons here bonded to four different groups well all the ch2 s they're bonded to another ch2 and then two H's I could draw it I could draw it like this H and H so they're bonded to two of the same groups so none of these none of these ch2s none of these CH 2 s are good candidates for being a chiral Center or chiral carbon they're both bonded to or all of them are bonded to two hydrogen's and then two other very similar-looking ch2 groups although you have you have to look at the entire group that it's bonded to but they're both they're all definitely bonded to two hydrogen's so it's not 4 different groups if we look at this CH right here we could separate it out like this we could separate the h out like this and so it's bonded to a hydrogen this carbon is bonded to a chlorine and then it's bonded to well it's not clear when you look at it right from the get-go whether this group is different than this group but if you go around if you were to if you were to kind of split if you were if you were to split it halfway like this or maybe another better way to think about it is if you were to go around if you were to go around this molecule in that direction the counterclockwise direction you would encounter a ch2 group and then you would encounter a ch2 group and then you would encounter third then you would counter a fourth ch2 group then you'd come back to where you were before so you would encounter 4 CH 2s and then you come back to where you were before if you go in this direction what happens you encounter 1 2 3 or CH 2 s and you come back to where that you were before so all of this kind of this bottom group depending on how far you want to extend it and this top group are really the same group so this is not this is not not not a chiral Center not a chiral not a chiral Center or not a chiral carbon it's not bonded to four different groups and this is also not a chiral molecule because it does not have a chiral Center and to see that it's not a chiral molecule let me see if I can backtrack this back toward the way I was wrote it right before so see that it's not a chiral molecule there's a couple of ways you could think about it the easiest way or the way my brain likes to think about is just to think about its mirror image it's Miriam it will look like this it's so if that's the mirror you would have a chlorine and then you have a CH ch2 ch2 and you have a ch2 ch2 and then you complete your your cyclopentane now in this situation is there any way to rotate this to get this over there well if you just took this molecule right here and you just rotated it 180 degrees if you just rotated this 180 degrees what would it look like if you just just complete well maybe a little over yeah about a about a well not quite 180 degrees but if you were to rotate it if you were to rotate it so that the chlorine goes about that far you would get this exact molecule you would get something it would look a little bit different it would look like this let me see if I can let me see if I can do it justice it would look like it would look like this you would have a ch2 so let me let me do it up here where we have a little bit more space so if I were to rotate this if I were to rotate this about that far I would get a CH you get the chlorine and then you have a and then you have your ch2 and then you have another CH ch2 ch2 and then you would have your ch2 up there if you were to rotate this all the way around or actually this is about this is exactly undred 80 degrees it would look like this and the only difference between this and this is just how we drew this bond here I could have easily instead of drawn that bond like that I could draw it facing up like that and these are the exact same molecule so this molecule is also is also not chiral now let's go to this one over here so I have a so what what is this this is bromo chloro fluoro methane just practice our naming a little bit but it's very clear that we are bonded to four different groups all of the different groups or the atoms in this case that are bonded to this carbon are different so this carbon is a chiral center chiral center and it should also be pretty clear that it is not it is also a chiral molecule if you were taking its mirror image and this is very similar to the example we did in the first video on chirality but it's mirror image will look like this you have the bromine on the right now the hydrogen is still and back and then you have the fluorine above it no matter how you try to rotate this thing if you try to get the bromine all the way over there all the way to that position then the hydrogen would be in this position and the chlorine would be in that position and no matter how you try to flip this around or rotate it or shift it you will never be able to superimpose this molecule on that molecule right there so that is a chiral Center and this is a chiral molecule chiral molecule and there's a word for these two versions these two versions we're going to go to the naming of them later on it's a little bit more involved we'll have a whole separate video on it but these two versions of bromo chloro fluoro methane they sometimes have different chemical properties and these are called enantiomers and then shimmers and enantiomers are just are just the the the the mirror images it each enantiomer is a mirror image of each other but they are stereo isomers so they are stereo these are all just this is all just terminology stereo isomers you're familiar with the word isomer and isomer just means that you have the same you have the same atoms in your molecule but then you have different types of isomers you have constitutional isomers that say okay you're different things are connected to different things stereo isomers are the same things are all connected to the same things you have a carbon connected to only a fluorine a claw a chlorine connected to the carbon a hydrogen connect to the carbon a bromine connect to the carbon so all of the same things are connected to the same things but they're three-dimensional configuration that's where we're dealing with the stereo part stereo chemistry is the study of three-dimensional three-dimensional chemistry as essentially understanding the actual three-dimensional structure of things so stereo isomers mean that we have the same we have the same constituents the same atoms they have the same constituent they have the same connections to each other bromine is still combing is still connected to carbon which is still connected to hydrogen that's all true over here but they're three-dimensional they're three-dimensional orientation is still different and in this case where they are mirror images of each other we call them enantiomers enantiomers and I should probably make one clarification in the last few videos I've been a little bit you know sometimes I'll say configuration and sometimes I'll use the word conformation so sometimes I'll use the word configuration and sometimes I use the word conformation and I actually should be a little bit more or I should have been a little bit more exact about these when you're talking about a configuration you're actually about talking about a different structure to go from one configuration to another configuration you would actually have to break bonds and kind of reassemble them so these are different configurations because in order for them to be able to be the same thing you would have to swap maybe the bromine and the hydrogen in there where they are relative to the carbon so these are different configurations confirmations are really just different shapes or different orientations of the same molecule so when we talked about cyclohexane being in a boat so this is cyclohexane being in a boat conformation or this is the cyclohexane being in a chair conformation it's the exact same molecule with the exact same connections we didn't detach any bonds or reattach any bonds they just flipped around a little bit so these are two different confirmations these are two different configurations to go from one configuration to another you have to rearrange bonds now let's look at this molecule over here can we identify any stereo centers or chiral carbons or chiral atoms and you have this carbon right here see this carbon right here it's bonded to a chlorine a hydrogen or bromine and then another carbon so this is bonded to four different things so this is this is a a chiral carbon and sometimes they put little asterisks there but if we look at this carbon right here you can well it's bonded to a fluorine another carbon but it's bonded to two different it's bonded to two hydrogen's so it's not chiral it has two of the same things that it's bonded to you can even see a little axis of symmetry through it if you look at that you can kind of flip it over and it's going to be the same thing but this one right here that is a chiral Center that is a chiral Center or chiral carbon or chiral atom or asymmetric carbon you'll see it used in different ways and because this molecule has got that chiral Center you'll see that if you were to take its mirror image it would be an enantiomer this is not superimposable on its mirror image we could even we could even try to draw it and just show you don't always have to do the mirror image on the right side we could draw the mirror image on the left side so if we want to draw its mirror image it would look like this you would have a fluorine carbon carbon chlorine you have your two hydrogen's and then you would have a hydrogen here and then you would have your bromine here no matter what you try to do if you try to flip this around or whatever you will never be able to superimpose this on top of this so these are enantiomers these are both Stier isomers really of relative to each other and either of these regardless of which one you pick are chiral molecules so these are chiral chiral molecules I'm over the time that I normally want to go in the video so in the next video I'll do even more examples of this