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Current time:0:00Total duration:11:04

Video transcript

so far we've dealt with simple chains and rings of carbons but let's think about what happens when things get a little bit more complex let me just draw a molecule here and we can think about how we'll name it so let me draw so let me let me draw it like let me draw it like that so here we don't have a simple chain it branches off at some point so what we do in this situation is we find the longest chain in this molecule and let's think about what the longest chain is if we start here we get one two three four five six seven eight carbons if we start here we get one two three four five six seven eight nine carbons so what we do is we look at the longest chain the longest chain is this one right here let me do this in a different color so this is one two three one two three four five six seven eight nine carbons and so this will be that will be kind of the core of our naming so it's nine carbons so that right here longest chain longest chain has nine carbons you can kind of view this as the backbone of our molecule and also the backbone of our naming nine carbons so we're dealing with a nonane nan Ain remember nine nan for nine and then Ain because we're dealing with an alkane we have all single bonds over here now what do we do with this thing over here well what's kind of sticking off of this chain well we essentially have we have one carbon here that's attached to the chain right this carbon is bonded to a carbon on the chain if we wanted to draw the entire molecule we could draw carbon here and it would it be bonded to three hydrogen's but that is all implicit but what is this thing right here well it's one carbon so you might be tempted to say it's methane but it's not methane because attached to other things but it would be right to use the prefix meth so this right here you would use the prefix meth so this is one one carbon so you would want to use the prefix meth but because it isn't part of it isn't the main chain it is added to something else we don't write methane we write methyl so let me write this right here mat fill methyl so this means this means that it is it branches off branches off longer chain longer chain so this this molecule right here would be called and actually there's one more thing that we have to think about this thing could have been we could just call it methyl nonane let me just write that down right now so we could just call this right from the get-go we could call it methyl methyl na named methyl nonane but there's one problem with just calling it methyl Nani this is methyl nonane but so it's let me draw it so this thing I just drew here this is 1 2 3 4 1 2 3 4 5 6 7 8 9 so that's the nonane and the one I drew here is 1 2 3 the the methyl is right over here that's what I just drew that is let me do it the same color so this is what I just drew but maybe what if it was something like this what if it was 1 2 3 4 5 6 7 8 9 and let's say that the methyl group was instead of being right here let's say the methyl group was right here so how would you name these two things differently this name right now does not differentiate between the methyl group being on this carbon versus the methyl group being on this carbon over here or this carbon over there and what you do in this case is you number the carbons on the longest chain on the main backbone and you number them so that the methyl group is attached to the lowest possible number so there's two possible ways to number this chain you could start here is 1 2 3 4 5 6 7 then you would say that this would be the methyl group is attached to the 7 carbon or you could start numbering from this end of the chain would be 1 2 3 or so it could also be attached to the 3rd 3 4 5 6 7 8 9 so you want to number it so you're closest to the methyl so you want to start here 1 2 3 4 5 6 7 8 9 so in this case this would not just be methyl nonane this thing right here would be 3 let me make this very clear it would be three methyl nonane because the methyl group that one carbon that one ch3 is attached to the third carbon on our nonane backbone so that right there is three methyl nani since i drew this out what is this right here well once again we have this nonane and backbone 1 2 3 4 5 6 7 8 9 and you want a number it so that this methyl group is at this at the lowest number carbon as possible so it's closer to this end than that end so it's 1 2 3 4 I'll do that in magenta and then you could keep numbering 5 6 7 8 9 so this one is going to be this one is going to be 4 and then you have your methyl group it's just one carbon sitting right there so for 4 methyl 4 methyl nonane 4 methyl nonane now let's go let's go the other way around let's say we start with the name and we want to figure out its formula and hopefully this will this this gives you a good a good understanding how things will get more complex and over the next few videos I'll get more and more complex but you'll see it's all at least reasonably logical so let's say I were to give you let's say I were to give you let's say I were to give you let me think of one let's say 2 - propyl propyl heptane - propyl heptane so how do we how do we take this apart so the first thing you see it is a it is an alkane it's all going to be single bonds heptane this is kind of the core so the longest chain here kept is the prefix for seven so this tells us let me make this clear this tells us that we're dealing with all single bonds single bonds single bonds that's what the Ain tells us if we had double bonds it would be een triple bonds ein we're going to see that in the future but let's stay simple right now the HEPT tells us that we were dealing with seven seven carbons seven carbons and then what does this to propyl means well propyl propyl tells us what was the what was the pro prefix if methyl is one ethyl is two propyl is 3 butyl is four so this is a three three carbon group three carbon group and it's going to be attached to the second carbon on the heptane so let me draw the heptane chain so we have seven carbons so one two three four five six seven and then on the second carbon on the second carbon so let me pick a good color here on the second carbon so if we just number it one two three four five six seven on the second carbon right there we have a propyl group we have a propyl group but there's a three carbon group so let me draw the propyl group so we have a 1 2 3 3 carbon group and it's attached at the second carbon right there so this molecule to propel heptane looks just like this let's do another one maybe one that seems a little bit more more difficult let's say that we have let's say that we have six let's say we have six butyl six butyl tetra decade tetra deca and all of these might seem a little daunting when you see it at first but if you really just break it up it actually is pretty logical so once again we have the Ain there so it's called going to be single bonds what is tetra deck what is that prefix well deck is 10 and then we have tetra that's 4 plus 10 that's 14 tetra deck is 14 so this is telling us that we're dealing with a 14 carbon chain 14 carbon chain so let's draw that so 1 2 3 4 5 6 7 8 9 10 11 12 13 14 carbon chain and if we number them 1 2 3 4 5 6 7 8 9 10 11 12 13 14 this tells us that the sixth the sixth carbon will be butyl will be a butyl group so let's see the six carbon is right here and butyl and you should memorize this methyl is one at the list - propyl is three butyl is four so we have a four carbon group so let me write this in pink maybe so this is a 4 4 4 carbon group 4 carbon it's actually called an alkyl group it's it's attached to something else so on the 6 carbon we have a 4 carbon group so 1 let me draw it this way no this is fine let's say it's let's say it's we have 1 2 3 4 so that is our butyl right there and it's just attached to the sixth carbon it's attached to the six carbon right there so this is what our molecule would look like now let me ask you a question would you ever see would you ever see a nine butyl tetra decade would you ever see a nine butyl texture decane so something where so let me redraw it like this let me so a nine butyl tetra decade so it would have a butyl over here one two three four one two three four would you ever see a nine butyl tetra decade will you ever see that written you might say oh yeah the digit Sal you just drew it and the reason why you won't ever see that written is because there's a better way to number it if it's like this instead of starting over here at one at this end you'd want to start one at that end so instead of saying nine butyl tetra decane you should number it the other way to say this is one two three four five six so this is actually also six butyl tetra decane I'm sure I got that that one two three four five six so instead of going instead of starting from the left and making this the ninth carbon you always want to start numbering from the direction that has a lowest number for the first group