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Current time:0:00Total duration:6:04

Entgegen-Zusammen naming scheme for alkenes examples

Video transcript

based on what we learned in the last video let's see if we can name these two molecules here so let's start with this blue one so the first thing we notice it is an alkene it has a double bond right there so we can write from the get-go right that it's going to end with n N and then we need to figure out what the longest carbon chain is and it looks like it's this one here 1 2 3 4 5 6 7 carbons so it's going to be HEPT it's going to be kept as our prefix on the alkene it's going to be let me write it out a little bit further to the left HEPT and then we have to figure out where the double bond is and we always want to start numbering our carbons from the direction that bumps into the double bond first and so the double bond is closer to this end of the chain than that ends we're going to start numbering here so 1 2 3 4 5 6 7 and so the double bond starts on the 3 carbon so it is HEPT it is HEPT 3e and we also have a functional group we have a methyl group sitting on the number 4 carbon so it is 4 it is 4 methyl 4 methyl HEPT 3 n which is correct but we still haven't considered what what's going on on either side of the double bond whether the higher priority functional group is or whether they're closer to each other on both sides of the double bond or whether they're farther away from each other and to do that we first have to identify the higher priority group on each side of the double bond so on the right side of the double bond let me circle it in magenta on each side so on the right side of the double bond we only have one functional group right over here you could view this as an ethyl group that's pretty obvious there is no other functional group bonded to the carbon there's only a hydrogen over here now on the left side it's a little bit less obvious we have two functional groups from the point of view of this carbon you have the methyl that we already pointed out and you also have these 3 carbons right over here you could view that as a propyl group and what we need to do to identify the highest priority group is to use the cahn-ingold-prelog namings or priority scheme that we learned several videos ago and there you literally go from this carbon you look at the you look at what it's bonded to and if this carbon and you compare the atomic numbers but in both cases it's a carbon to a carbon this is a carbon to a carbon so they're atomic numbers are the same so then you go one bond further away and you say which one is bonded to a higher atomic number atom this carbon bonds to a carbon which is a higher atomic number this carbon only bonds to three hydrogen's this one does two hydrogens and one carbon because it's bonded to another carbon it takes priority this propyl group is a higher priority functional group so now when we're trying to decide whether it is entgegen or zusammen we look at these two groups and we see that they are sitting on the same side of the double bond they're both above the carbons they are closer to each other so this is this molecule is zusammen or if we were doing which is on some levels you can think of the same thing as sis but sis and trans stop supplying when you start having more than two functional groups in this case we have three so we would call this we would call this Z Z for methyl HEPT 3 and that's because the higher priority functional groups are on the same side of the double bond now let's do this one over here and I someone pointed out rightly that I misspelled zusammen in the last video it's actually spelled like this zusammen I had spelt it with two S's and one M I guess you can forgive me I don't speak German but anyway thought I would point that out now let's try to let's try to label this thing right over here so the first thing this once again is an alkene let's identify the longest carbon chain here so it looks like 1 2 3 4 5 6 7 8 carbons double bonds are closer to the left-hand side so we'll start numbering here 1 2 3 4 5 6 7 8 so just the main chain is acht make sure I have some space here it is acht 3 acht 3 N and then we have some well we have one functional group sitting off of the main chain we have this bromine we have this bromine sitting right over there on the third carbon so we would call this three bromo three bromo acht three een and now we have to figure out is it ink again or zusammen so if we look on the carbon on the right hand side it's pretty obvious that this is the only functional group we just have a hydrogen there so let me circle it in the magenta just like that and then on the left hand side we have two functional groups we have this broom we could view this as a bromo or we have a bromine sitting right there and then we have this propyl group and because this propyl group is bigger you might be tempted to say it takes higher priority but remember in the con Engle Ingold prelog system you give higher priority to the atom that has a higher atomic number bromine has an atomic number of 35 carbon has an atomic number of only six so bromine is actually higher priority so this is the higher priority functional group right over here so now for deciding whether it's n kagan or zusammen we see that our higher priority groups are apart they're on opposite sides of the double bond this one is on top this one is below we are apart so this is entgegen and again or we would write e this is e 3 bromo acht 3 E and E is 4 just as a bit of a refresher it's 4 entgegen a word that I enjoy saying and gig in there you go