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Current time:0:00Total duration:11:34

Video transcript

if we look at the molecule on the left and try to use our assists trans terminology we quickly realize that we can't use it to use sister trans we would need to have two identical groups to compare and here we have four different groups attached to our double bond so we need to use a different system to find the configuration of our double bond we're going to use the e-z system so to use the ez system you need to think about atomic number to assign priority to the groups attached to your double bond so let's start with the carbon on the right side of our double bond we look at the atoms directly bonded to that carbon there's a hydrogen directly bonded to that carbon and there's an oxygen directly bonded to that carbon next you need to compare those atoms in terms of atomic number hydrogen has an atomic number of one and oxygen has an atomic number of eight they higher the atomic number the higher the priority so the group that contains oxygen is the higher priority group so this is the higher priority group and the hydrogen would be would be number two here now let's look at the left side of our double bond so let's look at this carbon and we look at the atoms directly bonded to that carbon there's a bromine directly bonded to that carbon and there's a carbon we go over here and we see that carbon has atomic number of six and bromine has an atomic number of 35 the higher the atomic number the higher the priority so the bromine gets higher priority so the bromine would get a number one and we give a number two to the methyl group next I like to draw a line to think about sides of our double bond if our two higher priority groups are on opposite sides of our double bond that is the e configuration and the e comes from the german word for opposite so if the two higher priority groups are on opposite sides of the double bond it's the e configuration let's look at the example on the right so it's very similar if we start on the right side of the double bond this carbon is still bonded to an H an O H and the O H group gets a higher priority because the oxygen has the higher atomic number so this gets a 1 and the hydrogen gets a 2 so that's the same as the previous example when we go to the left side of the double bond and we look at this carbon now I've switched the methyl group and the bromine we know the meta bromine gets higher priority because the bromine has the higher atomic number and so the methyl group gets a number 2 so when I draw a line here it's easier to see that the two higher priority groups are on the same side right the O H and the bromine are on the same side of our double bond this is the z configuration z comes from the German word meaning together so the two higher priority groups are together they're on the same side a good way to remember this is to think about the two higher priority priority groups being on Z same side and that is how that's one way to remember that the to higher higher priority groups being on the same side is Z so the easy system is more inclusive than the Syst trans terminology so easy is often a better way to come up with the configuration of a double bond let's assign a configuration to this double bond and let's start with the carbon on the left side we look at the atoms directly bonded to that carbon there's a bromine and there's a chlorine since bromine has the higher atomic number bromine gets the higher priority so bromine gets a 1 and chlorine gets a 2 if we go to the right side of our double bond we look at the atoms directly bonded to this carbon we know that here's a carbon and we know that here's a carbon so we have a tie because obviously carbon has the same atomic number so to break a tie we need to keep going so what I'm going to do is redraw this molecule and I'm going to do that over here on the right so we have a carbon bonded to a bromine and a chlorine and the carbon on the right is bonded to another carbon and this carbon me change colors here this carbon is this one which is double bonded to an oxygen so for the purpose of assigning priority we're going to pretend like this carbon is bonded to two oxygens obviously it has a double bond to only one oxygen but this will help us to assign priority and then we also have this carbon bonded to a hydrogen what about this carbon down here well this carbon is bonded to two hydrogen's and directly bonded to an oxygen and the oxygen is bonded to a hydrogen so let's go back to thinking about priority we started with the carbon on the right side and we got to these two carbons and then we had a tie so next we need to think about what atoms are directly bonded to those carbons so we'll start with this carbon up here this carbon is directly bonded to an oxygen and oxygen and a hydrogen so we write down oxygen oxygen hydrogen down here this carbon is directly bonded to an oxygen and two hydrogen's so oxygen hydrogen hydrogen to assign priority we look for the first point of difference so we start with the two oxygens and we have a tie so we go to the next atom and we have an oxygen versus a hydrogen obviously oxygen has a higher atomic number than hydrogen so this is our tiebreaker right right here is our first point of difference and so this group this group gets higher priority so this group gets a number one for priority and this group gets a number two next we draw a line here for our double bond and we look at our two higher priority groups our two higher priority groups are on the same side so Z's Ames IDE this is the Z configuration for our double bond so how do we incorporate the ez system into IU pact nomenclature let's say our goal is to name this alkene well we'd find the longest carbon chain that includes our double bonds and we'd give our lowest number possible to our substituents so that means starting from the right side here so this would be carbon one carbon two carbon three four five six and seven so what do we call a seven carbon alkene that would be hep teen so over here I will write hep teen and our double bond starts at carbon three so let me write three hep teen next we think about the substituents coming off of our carbon chain we have a methyl group coming off of carbon 2 and an ethyl group coming off of carbon four and we need to put those in alphabetical order so for ethyl would come first so let me go and put that right here so for ethyl and then we have two methyl three hep teen so that's the older way of naming it you could have also have written here for ethyl two methyl HEPT three so either one is is accepted now we have to think about our double bonds right is it an e configuration or is it a z configuration so let's start with I'll start with the carbon on the right side of our double bond here we know there's a hydrogen coming up this way and so we are comparing the atoms directly bonded to that carbon in red so we have a hydrogen here and then we have a carbon right here carbon has the higher atomic number so this group gets higher priority so we get a number one for this group and hydrogen would get a number two for the left side so we're thinking about this carbon right we think about the atoms directly bonded to that carbon well there's a carbon here and a carbon here so there's a tie so I'm actually going to redraw a part of the molecule here to help us figure out the higher priority group to help us break that tie so here's our double bond here's our hydrogen here's our carbons that's the right side of our we'll bond again only drawing in part of the molecule on the left side of our double bond we would have a carbon down here bonded to two hydrogen's and then this carbon has three hydrogen's so that's our ethyl group and then up here we would have a carbon bonded to two hydrogen's bonded to another carbon with two hydrogen's and finally bonded to a carbon with three hydrogen's alright now we have to figure out which of those two groups on the left side is the higher priority group so again let's start with the carbon on the left side of our double bond we look directly the atom bonded to that and it's a carbon so we need to continue on so this carbon is directly bonded to a carbon and then a hydrogen and then hydrogen's we have carbon hydrogen hydrogen what about this carbon that carbon is bonded to a carbon and two hydrogen's so we have carbon hydrogen hydrogen we look for first point of difference we have carbon versus carbon hydrogen and vs. hydrogen and hydrogen versus hydrogen so we don't have anything we still don't know which is the higher priority group so we need yet another tiebreaker so let's go to our next carbon so that's this carbon right here versus this carbon down here we'll go back up to this top carbon this carbon is bonded to a carbon and then hydrogen hydrogen so we have carbon hydrogen hydrogen down here let's look at this carbon we have hydrogen hydrogen hydrogen so hydrogen hydrogen hydrogen finally we have our first point of difference because we're comparing a carbon to a hydrogen so carbon has the higher atomic number so this group gets higher priority right so this group gets the higher priority let's go back up to this drawing alright we're talking about this group higher priority and our ethyl group gets a number 2 here so finally we go ahead and draw in our line alright so we can see which side our higher priority groups or which sides I should say our higher priority groups are on so our higher priority groups are on opposite sides of our double bond so we know that is ease the configuration of the double bond is e so we put that in our name so we put our e here and we put it in parenthesis so the final name for our compound is e for Ethel two methyl three hep teen or you could say e for Ethel two methyl hepps three e