Introduction to chirality

if I were to draw a hand let me just draw a hand really fast so I'll draw a left hand looks something like that that is a left hand now if I were to take its mirror image so let's say that this is a mirror right there and I want to take its mirror image and I'll draw the mirror image in green so it's mirror image would look something like this it looks something like this not exact but you get the idea the mirror image of a left hand looks a lot like a right hand now no matter how I try to shift or rotate this hand like this I might try to maybe rotate it 180 degrees so that the thumb is on the other side like this image right here but no matter what I do I will never get be able to make this thing look like that thing I can shift it and rotate it it'll just never happen I will never be able to superimpose the blue hand on top of this green hand when I say superimpose literally put it exactly on top of the green hand so whenever something is not superimposable on its mirror image let me write this down so this is not this is not super imposable on its mirror image mirror image we call it chiral we call it chiral so this hand drawing right here is an example of a chiral object or I guess the hand is an example of a chiral object this is not superimposable on its mirror image and it makes sense that is called a chiral it's called chiral because the word chiral comes from the Greek the Greek word for hand Greek Greek for hand and this definition of not being able to be superimposable on its mirror image this applies whether you're dealing with chemistry or mathematics or I guess just hands in general so if we extend this definition to chemistry because that's what we're talking about there's two concepts here there are chiral molecules chiral molecules and then there are chiral centers or chiral we'll call them chiral atoms they tend to be carbon atoms so sometimes they call them chiral carbons so you have these chiral and then you have chiral chiral atoms now chiral molecules are literally molecules that are not superimposable on their mirror image so not I'm not going to write the whole thing you know not superimposable I'll just write the whole thing not super imposable on mirror image mirror image now for chiral atoms this is essentially true but when you look for chiral atoms within a molecule you're the the best way to kind of spot them is that it's to recognize that these generally or maybe I should say usually usually are carbons especially when we're dealing with an organic chemistry but they could be phosphorus or Sulphurs but usually our carbons our carbons bonded to four different groups for different four different groups and I want to emphasize groups not just for different atoms and to kind of highlight a molecule that contains a chiral atom or chiral carbon we can just think of one so let's say that I have a carbon right here and I'm going to set this up so this is actually a chiral atom that the carbon Pacific is a chiral atom but it's part of a chiral molecule and then we'll see examples that are one or both of these are true so let's say it's bonded let's say it's bonded to a let's say it's bonded to a methyl group from that bond it kind of pops out of the page let's say it's there's a bromine over here let's say behind it there is a hydrogen and then above it we have a fluorine now if I were to take the mirror image of this thing right here we have your carbon in the center now going to do that same blue you have the carbon in the center and then you have the fluorine love the carbon you have your bromine now going in this direction you have this methyl group it's still popping out of the page but it's now going to the right instead of to the left so ch3 and then you have the hydrogen still in the back these are mirror images if you view this as kind of the mirror and you can see on both sides of the mirror now why is this chiral well no matter and it's a little bit of a visualization challenge but no matter how you try to rotate this thing right here you will never make it exactly like this thing you might try to rotate it you might try to rotate it around like that and try to get the methyl group over here to get it over there so let's try to do that but if we try to get the methyl group over there what's going to happen to the other to the other groups well then the hydrogen group is going or the hydrogen I should say the hydrogen atom is going to move there and the bromine is going to move there but this has the bromine in so this would be superimposable if this was a hydrogen and this was a bromine but it's not though you can imagine that hydrogen bromine are switched and you could flip it and do whatever else you want or try to rotate in any direction but you're not going to be able to superimpose them so this molecule right here is a chiral molecule and this carbon is a chiral Center so this carbon is a chiral is a chiral carbon sometimes called an asymmetric carbon or a chiral Center it sometimes you'll hear something called a stereo Center a serious Center is a more general term for any point in the a molecule that is asymmetric relative to the different groups that is joined to but they all of these especially you know when you're kind of an introductory organic chemistry class tends to be a carbon bonded to four different groups and I want to make that I want to stress that it's not four different atoms you could have had a methyl group here and a propyl group here and the carbon would still be bonded directly to a carbon in either case but that would still be a chiral carbon and this would still actually be a chiral molecule in the next video we'll do a bunch of a bunch of examples well we'll look at molecules try to identify the chiral carbons then try to figure out whether the molecule itself is also chiral