newman projections that'll be the topic of this lesson in my organic chemistry playlist now we're in the middle of an entire chapter on alkanes and we spent the whole first half of the chapter learning how to name alkanes and this latter half is looking at different ways that we represent alkanes the different conformations of alkanes and newman projection is a really useful tool for looking right down a carbon-carbon bond axis and a carbon-carbon single bond as long as it's not part of a ring is just free to spin just to rotate in space so to speak and the newman projection allows us to take a look at the different groups and their relationships as that bond rotates so and the relative energies of the different confirmations it adopts now if this is your first time joining us my name is chad and welcome to chad's prep where our goal is simply to make science both understandable and maybe even enjoyable really now this is my brand new organic chemistry playlist and i'll be releasing these lessons weekly throughout the 2020-21 school year so if you don't want to miss one subscribe to the channel click the bell notifications you'll be notified every time i post a new video so newman projections now before we get to a little more of a complicated example than the one we're going to start with so the standard place to start is what we call butane and we're definitely going to start there but rather than putting it on the format of the board here i think it'd be really instructive if you actually see a model of butane and match it up with the different conformations in a newman projection unfortunately my model kit is rather small as is yours in all likelihood and i highly recommend you build this model however if we take a look at my document cam it'll be a little easier to see what i mean so if you're going to understand newman projections i highly suggest you build a model similar to this one right here so rather than looking at a normal perspective here so if you look here this hydrogen right here is coming out at you it's a wedge and this one's coming out as well as a wedge and these two back here are both corresponding to dashes they're going away from you and then the methyl group here and the methyl group here both in the plane what we're going to do is we're going to turn this molecule 90 degrees and give ourselves a little bit different perspective and this is the perspective we're looking at when we look at a newman projection so in this case this would correspond to what's called the anti-conformation it's a special type of staggered conformation and you can see why they call it staggered because the three bonds coming off the front carbon that i can see are exactly in between the three bonds coming off the back carbon that i can see so hence that's a staggered conformation now there's an infinite number of possible combinations because we can just start rotating this one degree one degree one degree one degree you know out of time and so there's an infinite number of combinations and out of that infinite number of possible confirmations we only really draw six of them and we go to the extremes and that would be the high energy and low energy extremes and the staggered conformations here are the lower energy extremes so we're going to start rotating the 60 degrees at a time till we get back to this anti-conformation so as we rotate it 60 degrees apart we get to our first eclipse conformation you can see why they call it an eclipse conformation the front carbon's three bonds are exactly in front of the back carbon's three bronze hence eclipsing so and this ends up being higher energy and it's reason it ends being higher energy is the atoms are as close as they could possibly together so and the bigger the atoms the more they be bumping into each other we call it steric hindrance but also the electrons in the bonds are as close as they would ever be together and electrons being negatively charged that's a repulsion that's high energy as well so and again the atoms being near each other called steric hindrance so the bonds and the electrons repelling each other is called torsional strain so steric hindrance or steric strain and then torsional strain as well and those are the two reasons why these eclipsing interactions are the highest energy because we're gonna have the greatest amount of steric and torsional strain so if we rotate another 60 degrees we're going to be back to another so i went over a little bit there but back to another staggered confirmation so in this case this staggered is not near as good as the anti-conformation we had just a second ago and that's because this carbon and this carbon are now only 60 degrees apart so i'm being only sixth degree apart we call that a gauche interaction and so there's more steric hindrance associated with these gauche interactions uh than we had in the anti-conformation uh and in this case the bigger these groups are in the gauche interactions the higher energy they are and so oftentimes we'll rank different newman projections for a molecule based on how many gauche interactions it has as well as uh how large are the groups that are involved in these ghost interactions uh but keep in mind these ghost interactions are only ever in a staggered conformation we'd never talk about them in an eclipse confirmation if we rotate another 60 degrees clockwise here we're back to another eclipse conformation and this one's higher energy not as stable as the last one we had as well the last eclipsed and in this case because these two large methyl groups are now the ones eclipsing each other the bigger the group's eclipsing each other the higher energy as well so not all eclipsed are equivalent and not all staggered are equivalent let's rotate it another 60 degrees so and now we're to another staggered conformation and yet again we have another gauche interaction between the methyl groups so rotate it another 60 degrees we're back to another eclipse conformation not as bad as the last one equivalent energy to the first one we showed and then finally rotating it back another 60 degrees gets us back to our lowest energy most stable confirmation the anti-confirmation in this case a special staggered conformation so this is what i you know kind of the understanding you need it's helpful if you see it in a model and hopefully this helps but let's draw some pictures all right so now we've looked at butane we want to take a look at a little more complicated example here and some sort of variant of two chlorobutane and i say some sort of variant because it turns out there's two different what we call stereoisomers of two chlorobutane but you'll learn that in the next chapter so i don't want to get off on the side there but that's why i said some variant here so if with with two chlorobutane here common question you get on an ochem exam is simply draw the lowest energy conformation of this lovely molecule and they usually specify which bond you want to look down now in this case if you were numbering this to name this so we'd make sure that chlorine ended up on the lowest possible number and so we'd number it left to right instead of right to left and in our question i'm asking you to look down the c2 c3 bond axis and draw the lowest energy conformation so you want c2 to be the front carbon and c3 here to be the back carbon and as you recall we represent that front carbon with a dot and then we're going to have a circle representing that back carbon now we should also probably keep in mind that we're going to see all the bonds coming off of c2 and c3 except for that bond between them that's the invisible bond right behind that front carbon where we're looking in this case we'll put my red eye right there so and we're going to look right down that bond axis right there and we're going to see the chlorine coming off that front carbon and this methyl group right there coming off there but we'll also see the hydrogen that's on the dashed position so and on the back carbon we'll see the three other bonds coming off of it as well this methyl group right here and then also it's got a pair of hydrogens that are not drawn in and i want to draw those in just so we can find them on our newman projection here now cool now we could technically draw all six of the major confirmations and keep in mind once again that there's an infinite number of possible confirmations we just usually only draw the three eclipsed and the three staggered so however question on the test is usually just going to have you draw the lowest energy is a really common question that's the question at hand here and so knowing that we're looking for the lowest energy confirmation we can just ignore all the eclipsed conformations and just draw the staggered ones now we're looking right down the bond axis between c2 and c3 and if we're looking at it from the perspective of the molecule as it's drawn as it's provided on your study guide here then the bond that's in the plane is right below where we're looking and so on the front carbon we would have our bond in the plane that's right down the middle not on the left not on the right but pointing straight down not straight up so and then we'd have a bond off to the right and one off to the left now looking at from this perspective off to the right hand side here is going to be what's out in front of the board and then off to the left-hand side would be going into the board and keep in mind that's looking at it from this perspective so that i've got here but notice i could look down this c3c2 axis exactly backwards and now all of a sudden the wedged bonds going out in front of the board would be on my left hand side and the dashes would be on my right and so i just want to make sure you realize there's not like one way this is always gonna work it really depends on your perspective and so again i wanna look down the c233 bond axis just as it's drawn right here and so the way we look at this the bonds on the right again are gonna be so the wedge bonds coming out in front of the board and so that's going to be that chlorine right there so and then the bond on the left hand side are going to be the ones behind the board and that's going to be the hydrogen right there cool and then the bond straight down that's not on the right or the left because it's in the bond of the plane here that's the methyl group let's just draw him in as well okay so there's the bonds on the front carbon now the back carbon we represent with that circle again there's carbon 3 and as long as we're looking at the lowest energy confirmation we'll make sure we're looking at staggered conformations and it turns out this is represented being in a staggered conformation but if it wasn't we'd still be looking to just draw the staggered ones and so i've staggered the back carbon's three bonds we can see in between the front carbon's three bonds so we get a staggered conformation now if we look at that back carbon his bond that is straight up above where we're looking in this place that's where his bond to a methyl group is so and once again this wedged hydrogen is the one that's on the right when looking at it from this perspective and so it's on the right hand side of our diagram whereas the dashed one is the one on the left and i realize they're both hydrants so who cares but i just want to make sure you can identify them properly in case in your example you're on the hook four they're not the same cool so but this is one of our staggered confirmations and in this case i'm going to keep that front carbon exactly the same i'm going to rotate the back carbon clockwise and get the other two staggered conformations on the board here as well and so for that front carbon we still got the methyl at the bottom we've got the chlorine on the right and we've got the hydrogen on the left but now i'm going to take and rotate the back carbon around 120 degrees so and again the point is we're trying to draw the lowest energy conformation so we still want to draw a staggered conformation but we just want to get the other two and so in this case that methyl group is going to end up over here now so and these two hydrogens are going to end up in these two positions cool and finally one more time i'm going to rotate that back carbon 120 degrees yet again to get the last remaining staggered conformation here so again i'm going to leave that front carbon alone methyl groups on the bottom chlorines on the right hydrogens on the left so and now we can see that this methyl group is going to end up over here on the left hand side and those two hydrogens are in the other two spots okay now our goal here is to get that that goal here is to get that lowest energy confirmation and if that's the case if you're you're trying to dive between different staggered confirmations look for those gauche interactions so if we start with this first one here so we've got a gauche interaction right here and we call just a gauche interaction is always in a staggered confirmation and it's when you have two groups next to each other that are both not hydrogens they're both bigger than hydrogen and so in this case this is not a gauche because it involves hydrogen these are both hydrogens that's on a gauche this is not a gauche this is not a ghost this is not a ghost because they all involve at least one hydrant but this is a gauche interaction so we've got one gauche interaction in this conformation we've got two in this one and so so far this is a lower energy confirmation than the second one and then we'll go to the last one here and we've got one gauche interaction in this one so it's definitely they're going to be the first or the third that is going to be the lowest energy confirmation so you want the fewest gauche interactions to get the lower energy conformation but you also want gauche interactions if you have to have them so between smaller groups and so the real question comes down to so what's smaller a methyl interacting with a chlorine or a methyl interacting with another methyl and so it's really just a chlorine versus a methyl because they have one methyl in common the difference is the methyl versus chlorine and so and it turns out a carbon bonded to three hydrogens actually takes up more space and leads to greater steric interactions than a chlorine and so oftentimes we'll give you you know some kind of listing that kind of gives you a general idea of what you know kind of what energy's associated with maybe a gauche interaction with these groups and what you should know though is that a methyl group takes up quite a bit of space and an ethyl even more and so much so that the methyl actually takes up more than a chlorine and that's worth filing away in your head and so as a result the interaction between two methyl groups is going to be higher energy than this interaction between the methyl and the chlorine and so this first one it turns out is going to be our lowest energy confirmation that would be what we'd look to draw and again i drew all three so we could compare them and stuff like this but if you were doing this on a test you might be able to draw the first one and then kind of look at me like well if i rotate this back one around that's going to end up with two gauches and you might not even have to draw the second one and realize it and then you might look and say well if i rotated further around the methyl group would be over here and that would be a gauche between bigger groups and so you might actually get off the hook with not having to draw all three so however early on maybe you do need to draw all your staggered confirmations before you decide which one is the lowest energy now if you got something out of this lesson consider giving me a like and a share pretty much the best thing you can do to support the channel and if you're looking for practice problems on newman projections are 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