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Current time:0:00Total duration:13:06

Video transcript

so how do we name this molecule well we start with the longest carbon chain so there are seven carbons in my longest carbon chain so I would call this heptane and I number it to give the substituent the lowest number possible so in this example it doesn't really matter if I start from the left or from the right and both both examples you would end up with a four for your substituent there now this substituent looks different from ones we've seen before there are three carbons in it but those carbons are not in a straight chain alkyl group so if I look at it right there are three carbons but they're not they're not going in a straight chain they're branching of branching here so this is kind of weird how do we how do we name this substituent well down here I have the same substituent I'm going to draw this little zigzag line to indicate that that substituent is coming off of some straight chain okay and when you're naming a complex substituent like this you actually use the same rules that you would use for a straight chain alkane so you first identify the longest carbon chain which in this case is only two carbons right so that would be an ethyl group coming off of my carbon chain so I'm going to go ahead and name that as an ethyl group I'm going to go to head number it right to give mine to give my branching group they're the lowest number possible so I go one and two so what is my substituent coming off of my ethyl group well that's a methyl group coming off of carbon one so I name it as one methyl ethyl okay so now that complex substituent is named as one methyl ethyl so I could go ahead and put that into my name so coming off of carbon four I have I have one methyl ethyl and I'm going to put that in parenthesis and all of that is coming off of carbon four for my molecule so for one methyl ethyl heptane would be the I you pack would be an acceptable I you pack way of naming that molecule so if you're naming your complex substituent is one methyl ethyl that's the official I you pack way but there also names for these complex substituents so the common name for one methyl ethyl is isopropyl so I so propyl is the common name and isopropyl is used so frequently that that it's it's perfectly acceptable to use isopropyl for the name of this molecule as well so you could have said oh this is for isopropyl heptane and you would have been absolutely correct so that's yet another ayehu pack name so ISO means same and it probably comes from the fact that you have these these two these two methyl groups giving you this Y shape that are the same so so that's one complexes that you want one that has three carbons on it let's look at a bunch of complex substituents that have a total of four carbons on them so all all these guys have a total of four carbons and let's do that same trick with the zigzag line so we can ignore the rest of the molecule just think about them as being alkyl groups so how do I name these same steps you find your longest carbon chain so for this one the longest carbon chain would be three it's now keel group so it's propyl and when you number it all right this is getting one this is good a two and this is going to three so you have a methyl group coming off of carbon 1 here so it would be one methyl propyl as the name of that complex substituent the common name for that sec butyl so butyl because there are a total of four carbons let's do the next one so 1 2 3 again so when i when i number it 1 2 3 i can see that it would be propyl once again so i go ahead and write propyl here and what is coming off of that group right well i have a methyl group coming off of carbon 2 this time so it would be 2 methyl propyl so 2 methyl propyl for this complex substituent the common name for this is isobutyl so butyl again because there are four total carbons in this complex substituent i so because once again you have these two methyl so they're like the same so get that why formation so that's isobutyl the next one longest carbon chain there are two carbons in my longest carbon chain so that would be ethyl and when I number my longest carbon chain I can see that I have two methyl groups and each of those methyl groups is coming off of carbon 1 so I would say this would be one one die methyl ethyl so one one die methyl ethyl would be the I you pack name for for this complex substituent you will also see tert-butyl so tert-butyl is probably used even more frequently so tert-butyl again butyl because there are a total of four carbons here so those are the three possibilities for a complex substituent with a total of four carbons let's look at just a few of the possibilities for complex substituent that have five carbons they're actually much more than this but these are the ones that are most commonly used so let's just focus on on these two so once again we'll draw our zigzag line to represent the fact that this is actually connected to some to some straight-chain alkane and once again we find our longest carbon chain 1 2 3 4 so that would be butyl and when i number that carbon chain 1 2 3 4 I can see that I have a methyl group coming off of carbon 3 so it would be 3 methyl butyl for the I you pack name and this is also called isopentyl so you could say isopentyl since there are five carbons now and i so because again you have this methyl group in this methyl group looking like a why they're like the same thing or you've seen this I've seen is called ISO a male before so I saw a male or ISO pencil or acceptable I you pack names as well what about this one on the right longest carbon chain 1 2 3 so that would be propyl and numbering it 1 2 3 immediately it is obvious that you have two methyl groups coming off of carbon 2 so it would be to to die methyl propyl otherwise known as neopentyl since once again you have five carbons for these so again there are many more and we'll we'll stop with those and so that gives you an idea about how to approach naming complex substituents and of course when you name complex substituents you have to use them when you're naming straight chain or cyclo alkane molecule so let's look at a cyclo alkane molecule and let's see how to name this guy well I have four carbons in my ring and I have four carbons in this group so tie goes the cyclo alkane so remember from the last video if you have an equal number of carbons in your in your ring as with your your chain you're going to name it as an alkyl cyclo alkane the cyclo alkane wins the tie so there are four carbons so this would be cyclo butane so let's go ahead and write cyclo butane here and once you've determined that you're going to name it as a cyclo alkane then you have to look at this complex substituent and say okay well that's one two three so that would be propyl and then when you number when you number that complex substituent one two three obviously there is a a methyl group coming off of carbon 1 so you would write one methyl propyl so one methyl propyl and if you wanted to you could identify that one methyl propyl is coming off of carbon one of your cyclo butane so you could put this in parenthesis and write 1 1 methyl propyl cyclo butane or you could just just leave the one off and say one methyl propyl cycle butane because again it is implied what is the common name for for this complex substituent so one methyl propyl we go back up here and we find one methyl propyl was also called sec-butyl ok so we could have also have named this molecule ah sec-butyl cyclo butane so let's go ahead and write that so SEK util cyclo butane is a perfectly acceptable I you pack name as well so it just depends do you do you want to do it the official I you pack way or do you want to memorize some of these common names let's do one more thing in this video let's let's classify carbons okay so we're going to do something called classification of carbons this is a topic that comes up over and over again throughout in organic chemistry course so the earlier you learn this concept the better off you are so classification of carbons so let's say I have carbon connected to three hydrogen's and then I also have it connected to one other carbon in some art group I want to know how to classify this carbon so this carbon is connected to one other carbon so therefore we say it is primary so that is a primary carbon right there let's take off one of the hydrogen's and let's put on another our group so I'll make it our prime to distinguish it from the first art group so this time if I wanted to know the classification of this carbon it's connected to two other carbons so it is set to be secondary so it is a secondary carbon like that and I'm going to once again take off one of the hydrogen's so I'll make it an R double prime group and now if I wanted to classify my central carbon now this is going to one two three other carbons so it is said to be tertiary so that is a tertiary carbon like that and finally I have one more example of course I take off the last hydrogen's now I have our R prime R double Prime and our triple prime so what is the classification of this carbon now connected to four other carbons so it is set to be quaternary so that is a that is a quaternary carbon right here so so quaternary alright so if I'm trying to think about what where some of these common names come from alright I can see oh well all right here right here I have if carbons bonded to two other carbons well that would be secondary right so s-e-c for my prefix so let's go back up here and let's see if we can we can find those examples all right so here I have this carbon bonded to two other carbons so this carbon was said to be secondary so I think that's where this comes from I never seen that explain in a textbook or or anywhere but it just makes sense so it's ignoring the fact that this carbon is actually attached to a ring it's saying this carbon on my complex substituent is bonded to two other carbons so it is secondary on that complex on that complex substituent what about what about tertiary right so carbon bonded to three other carbons is said to be tertiary so if I go back up here again I can say well that would make sense because if I look at this carbon it's bonded to three other carbons right so I could say that is a tertiary carbon and once again I'm ignoring the fact that this carbon is actually bonded to another carbon on the ring okay so if you just look at the complex substituent that carbon is said to be tertiary which is I think is where the name comes from let's do let's do one more example of assigning complex assigning classification of carbons to this molecule so let's let's look at this carbon right here this carbon is bonded to one other carbon and three hydrogen's so this carbon is said to be primary this carbon right here is bonded to two other carbons so it is said to be secondary this carbon right here is bonded to three other carbons so it is tertiary this carbon is bonded to one other carbon so it is primary this carbon has bought it to three other carbons so it is tertiary and all the carbons on the ring right here are bonded to two other carbons so they are all set to be secondary so that's a very important skill to develop classifying your carbons again this will come up in future videos with different functional groups