In this video, we're going to begin our lesson on fatty acid nomenclature. Now, before we get started with the nomenclature, I first want to point out this modified version of our original lipid map, and this is here just to remind you guys that we're still talking about fatty acids here in this lesson and we have not yet moved on from talking about fatty acids. Also, a reminder that later in our course, we'll talk about the isoprenes but this is only after we finish talking about the fatty acids and all of our fatty acid-based lipids. But for now, we're talking about the fatty acids and specifically the nomenclature of these fatty acids. And, it turns out that there's actually several fatty acid nomenclature systems. There's a common naming system such as oleic acid here, for instance, naming this fatty acid. There's also a systematic naming system or 9 octadecanoic acid, again naming the same exact fatty acid. And then there's also a shorthand naming system, which is 18:1 Δ9, and again, this is just another name for the same exact fatty acid. So, in our next video, we're going to talk specifically about the shorthand naming system since this is likely going to be the nomenclature system that your professors want you guys to know. And so I'll see you guys in that next video where we introduce the shorthand naming system for fatty acids.
Fatty Acid Nomenclature - Online Tutor, Practice Problems & Exam Prep
Fatty Acid Nomenclature
Video transcript
Fatty Acid Nomenclature
Video transcript
In this video, we're going to introduce the shorthand naming system for fatty acids. Fatty acids can be assigned shorthand names using the following 4 step process that we have numbered down below as 1, 2, 3, and 4. Step 4 is only if it's necessary. Notice that in our example, we have a fatty acid that we can use to practice this 4 step process. The very first step is simply to count the total number of carbon atoms in the fatty acid. If we count the total number of atoms in this fatty acid down below, you'll find that there are 18 carbon atoms.
Now, the second step is simply to count the total number of double bonds that are present in the entire fatty acid, if there are any. When we take a look at this fatty acid down below, notice that there are actually 2 double bonds present in the hydrocarbon chain. What that means is we can indicate here that there are 2 double bonds. However, if there were 0 double bonds, then we would just put 0 for this number.
Step number 3 is simply to separate the first number here and the second number, here, by a colon so that we get the total number of carbon atoms, separating by a colon the total number of double bonds. We can go ahead and do that down below here. So what we have is 18 total carbon atoms and 2 total double bonds here and here.
The 4th step is only if it's necessary and that is if there actually are double bonds present, then you have to go to step number 4. But if there were 0 double bonds, then we would be done and we would not have to go to step number 4. Step number 4 is only to indicate the presence and location of any double bonds and you do that by using a superscript on the Greek letter delta. This triangle that you see right here is the Greek letter delta, and the superscript is really just an exponent. The superscript or the exponent really just indicates the lowest numbered carbon that's forming each double bond. When we take a look at our fatty acid down below, we want to indicate the presence and the location of these 2 double bonds.
Again, the way that we do that is we have to start by numbering the carbon atoms and we know that we usually number the carbon atoms starting from the carboxylic acid carbon. And so this would be carbon 1, the alpha carbon here, which is the one adjacent to the carboxylic acid carbon, it's gonna be carbon 2. This is carbon 3, 4, 5, 6, 7, 8. Notice that carbon number 9 right here is the first carbon atom of this double bond. It's the lowest numbered carbon, forming this double bond. That means that up here in the exponent for the delta, we're gonna want to put a 9 here to indicate the position of this double bond. And so, of course, this carbon is gonna be 10. This will be 11, this one will be 12, and notice that the 12 here is the first carbon of the second double bond, and it's the lowest numbered carbon indicating the presence of the second double bond. The next exponent here which is separated by a comma is going to be 12. This is the complete shorthand naming system.
For this fatty acid right here and, the common naming system for this fatty acid is Linoleic acid. We'll be able to get practice utilizing this shorthand naming system in our next couple of practice problems. I'll see you guys there.
Arrange the following fatty acids from lowest à highest melting point: 18:1Δ9 ; 18:0 ; 18:3Δ9,12,15 ; 18:2Δ9,12
a) 18:3D9,12,15 ; 18:2D9,12 ; 18:1D9 ; 18:0
b) 18:0 ; 18:3D9,12,15 ; 18:2D9,12 ; 18:1D9
c) 18:1D9 ; 18:0 ; 18:3D9,12,15 ; 18:2D9,12
d) 18:0 ; 18:1D9 ; 18:2D9,12; 18:3D9,12,15
Use the provided shorthand name to draw the structure of the fatty acid myristate (14:0).
Problem Transcript
Draw the structure of the fatty acid 24:2Δ5,9.