Naming alkenes examples

everything we've named so far has been an alkane we've seen all single bonds let's see if we can expand our repertoire a little bit and do some alkenes so let's see this look at this first carbon chain right here and I actually here I drew out all of the hydrogen's just to remind you that everything we were doing before with just the lines it really was representing something like this and when you start having the double bonds and we'll explain it in more detail later on it actually starts to matter a little bit more to draw the constituents because there's actually different ways that you can arrange it because these double bonds are you can imagine they're more rigid you can't rotate around them as much but you don't think about that too much right now let's just try to name these things so like we always do let's find out try to find the longest chain of carbons and there's only one chain of carbons here there's one two three four five six seven carbons in that chain so we're going to be dealing with HEPT we're going to be dealing with heft that is seven carbons seven carbons but it's not going to be an heptane heptane would mean that we have all single bonds here we have a double bond so this is going to be an alkene so this tells us right here that this we're dealing with an alkene not an alkane if you have a double bond it's an alkene triple bond alkyne we'll talk about that in future videos so this is kept-kept and you could we'll put an N here we'll put it in here but we haven't specified where the double bond is and we haven't numbered our carbons so when you see an alkene like this you start numbering closest to the double bond just like as this as if it was a alkyl group as if it was a side chain of carbons so this side is closest to the double bond so let's start numbering there 1 2 3 4 5 6 7 the double bond is between 2 & 3 and to specify its location you start at the lowest of these numbers so this double bond is at 2 so this is actually HEPT - 2 n so this tells us that we have a 7 carbon chain that has a double bond starting the een tells us a double let me write that down so this double bond right there that's what the Ian tells us double double bond between two carbons it's an alkene and the double bond starts if you start at this point the double bond starts at number two carbon and then it will go to the number three carbon now you might be asking but what if I had more than what if I had more than one double bond here so let me draw a quick example of that so let's say I have something like see 1 2 3 4 5 6 7 so this is the same molecule again 1 2 3 4 5 6 7 the way we drew it up here it would be it would look something like this but if I add another double bond what if we had another double bond sitting right here how would we specify this well once again we have 7 carbons 1 2 3 4 5 6 7 so we're still going to have a HEPT here and it's still going to be an alkene so we put our in here but we start numbering it once again closest to the closest double bond so 1 2 3 4 5 6 7 but now we have a double bond starting at 2 2 3 so it be HEPT 2 and we also have another double bond starting from 4 and going to 5 so have 2 2 comma 4 n that's what this molecule right there is now sometimes this is the I guess proper naming but just so you're familiar with it if you ever see it sometimes someone would write a hep to wean they'll write that as 2 hep diene and to probably because it's easier to say 2 heptane and from this you would be able to draw this thing over here so it's giving you the same amount of information and similarly over here they might say 2 for hep teen but this is the specific this is the this is the the correct way to write it lets you know that 2 and the 4 apply to the in which you know applies to double bonds let's do a couple more so over here I have a double bond and I also have some side chain so let's see if we can figure out how to deal with all of these things so first of all what is our longest chain of carbons so we have 1 2 3 4 5 6 and we could go in either direction does matter seven carbons or seven carbons and let's start numbering closest to the double bond double bond actually will take precedence over any other groups that are attached to it so let's take precedence well over any other groups in this case there will be other groups that will take precedence in the future but the double bond takes precedence over this side chain this methyl group so let's but it doesn't matter in this case we would want to start numbering at this end so it's one two carbon three carbon four carbon five carbon six carbon seven carbon so we're dealing with the HEPT again so it is we're dealing with a heft and we have a double bond in the starting from the second carbon to the third carbon so this thing right here this double bond from the second carbon to the third carbon so it's HEPT two comma three een i'm sorry not two comma three to e you don't write both endpoints three if I there's a three then that would have been a double another double bond there it's HEPT - two - e and then we have this methyl group here which is also sitting on the second carbon so this methyl group this methyl group right there so on the second carbon so we would say two methyl two methyl kept to e so it's a HEPT - een that's all of this part over here double bonds starting on the - if we're numbering from the right and then the methyl group is also attached to that second carbon let's do let's do one more of these so we have a cycle here and once again the root is going to be the largest chain or the largest ring here and our main ring is the largest one and we have one two three four five six carbons so we are dealing with we are dealing with hex as our root for kind of the core of our structure and it's in a cycle so it's going to be cyclo X so let me write that so it's going to be cyclo hex but it has a double bond in it so it's cyclo hex cyclohexene let me do this in a different color so we have this double bond here and that's why we know it is an N now you're probably saying hey Sal how come we didn't have to number where the ian is so if you only have one double bond in a ring it's assumed that one endpoint of the double bond is your 1 carbon so this when you write just cyclohexene you know so if you know cyclohexene it would look just like this would look just like this it could just like that you don't have to specify where it is it's just one of these are going to be the double bond now when you have other constituents on it by definition or I guess the proper naming mechanism is one of the endpoints of the double bond will be the 1 carbon and if any of those endpoints have something else on it that will definitely be the 1 carbon so this is one of the these both are kind of the candidates for the 1 carbon but this point right here also have this has this methyl group so we will start numbering there 1 and then you want a number in the direction of the other side of the double bond 1 2 3 4 5 6 so we have three methyl groups one on one so these are the let me circle the methyl group so that's a methyl group right there that's a methyl group right there that's just one carbon alright so we have three methyl groups so this is going to be it's going to add set the 1 the 4 and the 6 so it is 1 comma 4 comma 6 we have 3 methyl groups so it's tri methyl tri tri methyl cyclo hexane 1 4 6 tri methyl cyclohexene that's what that is hopefully you found that useful