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Current time:0:00Total duration:8:19

Video transcript

let's try to name this molecule right over here and so the first thing we want to do is identify the longest chain of carbons so let's see it could be 1 2 3 4 5 6 7 8 or let's see maybe it's 1 2 3 4 5 6 7 8 9 10 yes indeed that's the longest chain and if you go 1 2 3 4 5 6 7 or 1 2 3 4 5 6 7 so those aren't the longest so the longest one is this one 1 2 3 4 5 6 7 8 9 10 10 carbons and this is going to be an alkane because it's all single bonds and a alkane with a alkane that's a chain of 10 carbons we would use the prefix Dec for 10 so this is a decane let me write that right over here this is a decane decane now let's think about the groups that are attached to this decane so we have this group right over here this has two carbons in it one carbon two carbons and so we because it has two carbons we would use the prefix F remember meth is one carbon F is two carbons and since it's a group that we're not talking about the backbone this is an ethyl group this is an ethyl group and we have another ethyl group right over here two carbons attached right over here this is also an ethyl group and now this group right over here is interesting we can count the carbons in it so it has one two three carbons so you could think about well this has three carbons our prefix for three carbons is proq so you could say maybe this is a propyl group this right over here this right over here you could say maybe this is a propyl group and you wouldn't be completely off-base by saying that but we have to be a little bit more kick a little bit a little bit more careful when we name it because a propyl group you would assume that you're attaching to one end of the propyl group but we're not attaching to one end of the purple propyl group we're attaching essentially to the second carbon to the middle carbon and this is a secondary carbon the reason why it's called why it's called a secondary carbon is because it's attached to two to two other carbons if it was attached to three other carbons it would be a tertiary carbon if it was attached to only one carbon it would be a primary carbon so you could call this since we're attached to the second the secondary carbon right over here this is sometimes called a sec a sec propyl group a sec propyl group and it's also sometimes called isopropyl an isopropyl group isopropyl and then you'll actually see isopropyl a little bit more frequently and these are these would both be referred to as common names common names for this group now if you wanted to name this systematically then you would do it very similar to the way that you would name the entire molecule you would look for the longest chain here and the longest chain in this molecule starting starting with where you are attached is a chain of two carbons is a chain of two carbons and so you could call so that the backbone right over here is ethyl is let me write this right over here is ethyl it's an ethyl backbone here and then you could have you could view this carbon as a group attached to that ethyl backbone and we would start counting we would start counting right where we are attached to the main chain so this is the one carbon this is the two carbon so this right over here this is just one carbon group this right over here is an methyl group or a methyl group this is a methyl group so you have a methyl group attached to the one carbon of an ethyl group so the systematic name for this and this is a little bit less typical for for a group as small as a propyl group but you could call this one methyl one one methyl one methyl ethyl one methyl ethyl is a systematic name for this now the systematic name you might say hey why go through the pain of doing this for something so simple that we could just call isopropyl this is useful if this was a much large a much more complex group that was attached to this main chain but more typically and this is why it's called the common name you'll see this thing right over here just called isopropyl and sometimes you would call it C it's called a sec propyl or even s propyl now that we've named all of the groups let's think about what carbons they are attached to and where we can start counting from and the way that this is done is that you would start counting from the end from the end of your carbon chain your main this kind of this decane backbone and you would count from the end that bumps into the most groups faster so for example if you count from this end this would be the one carbon two carbon three carbon four carbon five carbon on the five carbon we bump into two groups if we started over here this would be the one carbon two carbon three carbon four carbon five carbon on the five carbon we do bump into a group but only one group and we'd have to wait till a six carbon to bump into two groups so so we get to the two groups faster we would start counting on this end so this is one carbon two carbon three carbon four carbon five carbon six carbon seven carbon eight nine and ten carbon and so when we think about which one which groups are we going to refer to first do we refer to the ethyl groups first or do we refer to this isopropyl group first we just think about the what what letter they start with in alphabetical order so for example these ethyl groups they clearly start with an E they clearly start with an e e comes before in the alphabet then the I and isopropyl before the P and sec propyl you would normally ignore the sec or the tert when you're thinking about alphabetical order and a also comes before the comes before the M in methyl ethyl so we will talk about the ethyl groups first so remember our backbone ten carbons all single bonds it's an alkane since there's ten of them it is decane and so let's talk about the Ethel's first and since we have two Ethel's we can say that this is diethyl so let me write that down so we can write diethyl die ethyl and of course we need to specify where those two Ethel's are one is that the five carbon one is at the six carbon so we could call this five five six diethyl that refers to the five refers to this ethyl group six refers to this ethyl group and now we could talk about the isopropyl group the isopropyl group is also on the five carbon so we could say we could say five six diethyl five five isopropyl ISO propyl isopropyl decane or if we wanted to use SEK propyl instead of isopropyl we could write SEK propyl here or if we want to do the systematic naming we could call this five comma six die die ethyl five instead of writing isopropyl here we could write all of this one methyl ethyl here so actually let me just copy and paste that let me just let me just copy this one methyl ethyl right over here copy and paste let me stick that there one methyl ethyl and of course the main backbone is decane decane decane so either one all of these are reasonable ways to name it this would be the common way where we use isopropyl here we're doing it more systematically by calling that group one methyl ethyl