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Current time:0:00Total duration:13:36

Stereoisomers, enantiomers, diastereomers, constitutional isomers and meso compounds

Video transcript

in this video we're going to look at pairs of molecules and see if they relate to each other and any in any obvious way or maybe less than obvious way so these first two right here they actually look like completely different molecules so your gut impulse maybe you see these these are completely different molecules and it wouldn't be completely off but if we look a little bit closer you see that this guy on the Left has one two three four carbons and so does this guy on the right has one two three four carbons this guy on the left has two four six seven eight hydrogen's this guy on the right has two four six eight hydrogen's and they both have one oxygen so both of the molecular formulas for both of these things are four carbons eight hydrogen's and one oxygen they're both c4h8 oh so they have the same molecular formula made up of the same thing so these are going to be isomers they're going to be isomers and there are special type of isomers in this situation we don't have the same bonds we're made up of the same things but the bonds what is connected to what is different so we call this a constitutional isomer constitutional constitutional isomer so we are essentially made up of the same things but we are actually two different molecules actually two very different molecules here now let's look at this first guy or this next guy over here so if we look at this molecule let's see does look like this carbon is chiral it is an asymmetric carbon it is bonded to four different groups for een bromine hydrogen and then a methyl group and so's this one and they've both made up of the same things you have the carbon and not only are they made up of the same things but the bonding is the same so carbon 2 14 carbon 2 a fluorine carbon 2 a bromine carbon 2 bromine carbon to hydrogen in both and then carbon 2 the methyl group and both but they don't look quite the same are they mirror images well no this guy's mirror image would have the fluorine popping out here the hydrogen going back here and then we have the bromine pointing out here let's see if I can somehow get from this guy to that guy let me let me flip this guy first so let me a good thing to do would be - would be to just flip see the fastest way I could potentially potentially get there well let me just flip it like this so I'm going to flip out of the page you can imagine I'm going to flip it like this so I'm going to take this methyl group and then put it on the right-hand side and you could imagine i'm going to turn it so it would come out of the page and then go back down so if i did that what would it look like i would have the carbon this carbon here i would have the methyl group on that side now and then since i flipped it over the bromine was in the plane of the page it'll still be in the plane of the page but since i flipped it over the hydrogen which was now it which was in the back will now be in the front the hydrogen will now be in the front and the fluorine will now in the back because i flipped it over so the fluorine is now in the back now how does this compare to that let's see if i can somehow get there well if I take this fluorine and I rotate it to where the hydrogen is and I take the hydrogen and rotate it to where that's all going to happen at once to where the bromine is and I take the bromine rotate to where the fluorine is I get that so I can flip it and then I can rotate it around this I guess this bond axis right there and I would get to that molecule there so even though they look pretty different with a flip and a rotation you actually see that these are the same molecule same same molecule next one so let's see what do we have here let me switch colors so over here this part of both of these molecules look the same you have the carbons on both of them this carbon looks like a chiral Center it's bonded to one two three different groups these are you might say oh it's two carbons but this is a methyl group and then this side has all this business over it so this is definitely a chiral carbon and over here same thing it's a chiral carbon and this has the same thing it's bonded to four different things so each of these molecules have two carbons and it looks like they have they're made up of the same things and not only are they made up of the same things but they the bond the bonds are made in the same way so this carbon is bonded to a hydrogen and a fluorine and then two other carbons same thing hydrogen and a fluorine carbon it looks like it's a hydrogen it's bonded to a car hydrogen and a chlorine so all of it's made up of the same constituents and they're bonded in the same way so these look like these look like but the bonding is a little bit different over here on this one on the left the hydrogen goes in the back and over here the hydrogen to the front and over here the chlorines and back and over here the chlorines in front so these look like stereo isomers stereo isomers you saw earlier in this video you saw structural isomers made up of the same things but the connections are all different stereoisomers they're made up of the same thing the connections are the same but the three-dimensional configuration is a little bit different for example here on this carbon it's connected to the same things as this carbon but over here the fluorines out front and over here out here the fluorine is out front over here the fluorines backwards and same thing for the chlorine here it's back here and its front here now let's see if they're related in it I guess in a more nuanced way well if you put a you could imagine putting a mirror behind if you put a desolated visual imagine putting a mirror behind this molecule if you put a mirror behind this molecule what would its reflection look like so if you put a mirror behind it in the image of the mirror this hydrogen would now since the mirror is behind this whole molecule this hydrogen is actually closer to the mirror so then the mirror image you would have a hydrogen that's pointed out and then you would have the carbon and then you would have the fluorine being further away and same thing in the mirror image here you would have the chlorine coming closer since this chlorine is further back closer to the mirror and then you would have the hydrogen pointing outwards like that and then obviously the rest of the molecule would look would look exactly would look exactly the same and so this mirror image that I just thought about in white is exactly what this molecule is hydrogen pointing out in front hydrogen pointing out in front Chloe you know you might say wait this hydrogen is on the on the right this one's on the left it doesn't matter this is actually saying that the hydrogen's pointing out front fluorine is pointing out back hydrogen up front fluorine back chlorine out front hydrogen back chlorine out front hydrogen back so these are actually mirror images but they're not the easy mirror images that we've done in the past where the mirror was just like that in between the two these are this one is a mirror image where you place the mirror either on top of or behind one of the molecules so this is a class of stereoisomers and we've brought up this word before we call this enantiomers enantiomer so each of these are an enantiomer I'll say they're enantiomers of each other they're stereo isomers they're made up of the same molecules so that they have the same constituents they also have the same connections and not only do they have the same connections that that so far gets a sister isomer but they're a special kind of stereo isomer called an enantiomer where they are actual mirror images of each other now what is this one over here in blue just like the last one looks like it's made up of the same things you have these carbons these carbons these carbons and hydrogen's up there same thing over there you have a hydrogen bromine hydrogen and a bromine hydrogen and chlorine hydrogen chlorine hydrogen chlorine hydrogen chlorine so it's made up of the same things they're connected in the same way so they're definitely stereo isomers well we have to make sure they're not that well let's make sure they're not the same molecule first here hydrogen's in the front there hydrogen's in the back here hydrogen is in the back here hydrogen in the front so they're not the same molecule they have a three a different three-dimensional configuration although their bond the the bond connections are the same so these are stereo isomers these are stereo I stereo isomers well let's see if there are nan chalmers so if we look at it like this you put a mirror here you wouldn't get this guy over here then you would have a chlorine out front and a hydrogen so you won't get it if you get a mirror there but if we do the same exercise that we did in the last in the last pair if you put a mirror behind this guy if you put a mirror behind this guy and I'm just going to focus on stuff that's just forward and back because that's that's what's relevant if the mirror is sitting behind the molecule so the mayor is sitting behind the molecule this hydrogen or this bromine is actually closer to the mirror then that hydrogen so the bromine will now be out front and then the hydrogen will be in back this hydrogen will be in the back I'm trying to if you're trying to do a kind of a mirror image if it's hard to conceptualize and then that would all look the same and then this chlorine will now be out front and this hydrogen will now be in the back in our mirror image if we can visualize it and then we have another one and then this chlorine is closer to the mirror that's kind of it's sitting on top of so in the mirror image it would be pointing out and then this hydrogen would be pointing back now let's see our is our mirror image the same as this so in the mirror image our bromine is pointing in the front hydrogen in the back there then we have hydrogen and in then in our mirror image we have the hydrogen back chlorine in front same there so so far it's looking like a mirror image and then in the this last carbon over here chlorine in front hydrogen and back but here we have chlorine in the back hydrogen in front so this this part you can think of it this way this is the mirror image of this this is the mirror image of this part but this is not the mirror image of that part so when you have a when you have a stereoisomer that is not a mirror when you have two stereoisomers that aren't mirror images of each other we call them diastereomers I always have trouble saying that let me write it it these are these are diastereomer diastereomers which is essentially saying it's a stereo isomer that is not an enantiomer that's all it means stereo isomer not in answer Maria steer isomer it's either going to be an enantiomer or a diastereomer now let's do this last one let's see we have to site we have this we have this kind of cyclo hexane ring and they have a bromo on on I guess the number one and the number two group depending how you think about it looks like they are mirror images of each other we could put a mirror right there and there definitely they look like mirror images and this is a chiral carbon here it's bonded to one carbon group that is different than this carbon group this carbon group has a bromine this carbon group doesn't have just has a bunch of hydrogen's on it if you kind of go in that direction so and it is hydrogen and then a bromine so that is chiral and then same argument that is also chiral and obviously this one is chiral and that is chiral but if you think about it they are mirror images of each other and they do have two they each have two chiral centers or two chiral carbons but if you think about it all you have to do is flip this guy over and you will get this molecule these are the same molecules so it is the same molecule so this is interesting and we saw this when we first learned about chirality even though we have two chiral centers this is not a chiral molecule it is the same thing as its mirror image it is superimposable on its mirror image it is it is super imposable imposable on its mirror image mirror image so even though it has chiral carbons in it it is not a chiral molecule and we call these meso compounds meso compound this is a and we could point to one of them because they really are the same compound this is a mezzo mezzo compound it has chiral centers it has chiral carbons I guess you could say but it is not a chiral compound and the way to spot these fairly straightforward is that you have chiral centers but there is a line of symmetry here there is a line of symmetry right here these two and these two sides of the compound are mirror images of each other now this these would not be the same molecule if this was if I change that to a fluorine and I changed that to a fluorine then all of a sudden you do not have this symmetry these are mirror images but they would not be superimposable so that was a fluorine these would actually be enantiomers and this would not be only one meso compound it would be two different enantiomers and one of them would probably would have a would have a our direction and one of them would have an S direction if we go with the with the naming conventions that we learned in the last few videos