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Current time:0:00Total duration:11:12

Video transcript

in the last video we visualized an ethane molecule with a Newman projection what I want to do in this video is show that you can really visualize longer chains or even we'll see in future videos even a cyclical ring based carbon molecules with Newman projections as well and I guess the next most complex molecule to study would be butane butane we could do propane but butane will be interesting this was ethane right here butane will have four carbons and if I were to draw it in kind of a ball and as a ball and stick model it would look like something like this so this would be one carbon right there then you would have another carbon right over there and another carbon right over there and then you would have your fourth carbon and then your hydrogen's you would have a hydrogen coming out like this like that and then up like that this guy would have two hydrogen's that would stick out like that this guy would have two hydrogen's that stick out like that and then finally this guy will also have three hydrogen's to ch3 just like that now if we try to draw a Newman projection here's like well you know what do you consider the front or the back carbon and all of that and you actually can pick and what's interesting in the butane molecule is if you pick if you pick this guy if you pick so this is the 1 2 3 4 carbons if you pick the 2 carbon as our front and our 3 carbon as our back and then we view this carbon the ch3 is kind of one of the add-ons onto that carbon you can then do a Newman projection so let's try to do this so this will be the front one so we'll put this carbon in the front and we'll put this carbon over here we'll put this carbon over here in the in the back and before I even drew them you draw the Newman projection let me redraw this but I'm just going to draw this a set of with the hydrogen's the bonds explicitly defined I'm just going to call this a ch3 so let me re let me redraw this so I'll do this in orange so you have this carbon I'll do this kind of as a modified ball-and-stick so that carbon it has a hydrogen it has that hydrogen and that hydrogen and instead of drawing this out I'm going to just draw this whole thing this whole thing right here and I'll do it in I'll do it in magenta I'm going to draw this whole thing is just a ch3 so I'm going to draw this whole thing as just a ch3 so I'll draw it really big because it's not just one atom it's four atoms so this is our ch3 and well to do ball-and-stick everything really should be a ball so I'll draw a ball there ball there so that's our carbon number two and then it has this bond it has this bond over here to this carbon number three which when we do our Newman projection we'll put in the back so our carbon number three is like that and then the carbon number three it has two hydrogen's and then it has this it has this you can kind of view it as this methyl group attached to it if you want it has this CH it has this ch3 attached to it right there so I'll do the ch3 I'll do it in this blue color and so we could draw it like this so the ch3 is coming off so I'll draw it really big because it's not just one atom so it's a ch3 and then you have your two hydrogen's and then it's sorry you have your two hydrogen's down here so let me be very clear here so let me this this hydrogen that hydrogen that's that hydrogen and that hydrogen this thing here is that thing there that big ball right there is this whole ball and then let me find it I'll do green this hydrogen and this hydrogen is that height this hydrogen and this hydrogen and when you look at it this way nicely oh now I can see how I would draw a Newman projection I put this in the front that in the back I treat this whole part of the molecule as just a group if you will it is a group so let's do the Newman projection here and then we can think about where it's most stable so the way I've drawn it right here so you have your C I'll do this as the front this carbon 2 is going to be the front molecule so you have this CH you have the ch3 group going down and you have these two hydrogen's you have these two hydrogen's hydrogen and hydrogen that's the front and in the back you have this blue one you can imagine in the front if we want to maybe I'll do a little small orange thing to show this is the orange carbon and then the blue carbon is going to be in the back the blue carbon is in the back draw it like this so that's my blue carbon and the way we've done it here we have a ch3 pointing straight up and then we have our two hydrogen's we have our two hydrogen's now just like we talked about in the first video on Newman projections all of these groups have these hydrogen's have electron clouds around them this whole ch3 group has a larger electron cloud around it it's a carbon atom plus hydrogen's they all want to get away from each other the ch3 is even a bigger molecule so to some degree it's going to play a bigger role in whether something is a higher or lower potential energy or whether it's wound or not so I guess the most obvious or maybe it's not obvious but the ch3 group since they they have the biggest electron crowd they're kind of crowding the molecule the this ch3 group and this ch3 group or they're going to get as far away from each other as possible so the way we did this it looks kind of like our staggered conformation but when we're dealing it with actual methyl groups that are separated as far as they can from each other we call this the anti conformation we call this the anti conformation right here anti conformation and if we think about dihedral angles between the two methyl groups the dihedral angle here the dihedral angle here is 180 degrees 180 degrees dihedral angle and this is the lowest lowest potential energy potential energy or the most stable and that confuses you when I talk about lowest potential energy just think about it a rock on the ground has a lower potential energy than a rock that is 50 feet in the air a rock on the ground is also more stable it's less likely to do something something 15 feet in the air maybe if you nudge it a little bit it'll fall off the cliff or wherever or maybe it's already falling who knows it's going to move when you have higher potential energy or takes very little for it to release energy but when you have lower potential energy you're more stable so this is the most stable conformation now what are the other situations you could do here well you could keep rotating these let's say let's say we rotated the back the back carbon around clockwise what are the other confirmations we could get and so let me just let me just draw the front portion right here so you have your ch3 you have your ch3 and then you have your two hydrogen's hydrogen and hydrogen and let me copy and paste this so there's two other real economy there's everything in between but these are the ones that are interesting control copy and then let me let me copy it copy and then paste so I'll draw I'll actually draw three of these so then you can have that and then let me paste it one more time then you have that so these obviously this would be the front the front carbon and all sits in every situation if I want I could put make it a little orange dot to show that that's the front carbon and then let me draw the back carbon I should have copied and pasted this is well so you have your back carbon in every situation now if we were to rotate this if we were to rotate this character by sixty degrees if we were to rotate actually if we were to rotate the back by sixty degrees what would it look like well then we would have we would have this hydrogen would move up there so then you would have this hydrogen actually if we were to move it by 120 degrees I should say this would be 60 and then another 120 degrees so this hydrogen would go up there this hydrogen would go up there this methyl group would now be over here and then this hydrogen would go over here so we've just rotated the whole thing by 120 degrees we've rotated by 120 degrees now this conformation this was called the anti conformation it's the most stable because the carbon the methyl groups are as far away from each other as possible this right here is called the Gauss Khan for me the gauss confirmation let me do this different this is the gouge confirmation and you can view this as the second most stable at least the methyls are staggered they're not directly behind each other so here the methyls are as far apart from each other as possible if you look at the ball and stick model IG drew it in that conformation right here they're as far apart from each other if you were to flip this molecule if you were to flip it this methyl would get closer to this methyl and their electron clouds would start to crowd each other so in this situation this is anti most stable if you rotate it a little bit they'll get a little bit closer but they'll still be staggered you get the gautsche conformation now if we rotate this if we rotate the back guy now 60 degrees 60 degrees clockwise so if we rotate it just 60 degrees clockwise what's going to happen what's going to happen well then you're going to have any clips conformation where the carbons are directly but where the the methyl groups are directly behind each other and that's going to be your least stable situation all right so you would have your you would have this guy and I'll draw it slightly so you'd have this guy you know ch3 there and then you would have your hydrogen's that are right behind each other so a hydrogen and a hydrogen so in this situation were eclipsed this is the least stable least stable and also the most potential energy and then if we were to go another sixty degrees from this then we go to another gautsche conformation if you rotate this another sixty degrees then you'd have a ch3 here and then you would have this hydrogen would be up here and then this hydrogen here so this is staggered the CH the the methyl groups are at least they're not directly behind each other but they're not as far as they could be if we were to rotate another 120 degrees and get to the anti conformation so this one right here is also a gouge conformation so hopefully you understand now that if you just have to pick two carbons and then you can if there's kind of big things attached to each of those carbons you can just represent them as groups and when you do that you can really you'd use a Newman projection for any part of a molecule and when you do that you can start to think about how it can rotate and what parts or what what versions of it will be more or less stable