Fatty Acid Nomenclature: Videos & Practice Problems

Fatty acid nomenclature involves several systems, including common names like oleic acid, systematic names like 9-octadecanoic acid, and shorthand names such as 18:1 Δ9. The shorthand naming system follows a four-step process: count carbon atoms, count double bonds, separate numbers with a colon, and indicate double bond positions using the Greek letter delta. For example, linoleic acid is represented as 18:2 Δ9,12, highlighting its structure and double bonds. Understanding these naming conventions is essential for studying fatty acids and their roles in biological systems.

Fatty Acid Nomenclature

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

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 ; 18:3Δ^9,12,15 ; 18:2Δ^9,12 


a) 18:3D^9,12,15 ; 18:2D^9,12 ; 18:1D⁹ ; 18:0
b) 18:0 ; 18:3D^9,12,15 ; 18:2D^9,12 ; 18:1D⁹
c) 18:1D⁹ ; 18:0 ; 18:3D^9,12,15 ; 18:2D^9,12
d) 18:0 ; 18:1D⁹ ; 18:2D^9,12; 18:3D^9,12,15

• A. 18:3Δ^9,12,15 ; 18:2Δ^9,12 ; 18:1Δ⁹ ; 18:0
• B. 18:0 ; 18:3Δ^9,12,15 ; 18:2Δ^9,12 ; 18:1Δ⁹
• C. 18:1Δ⁹ ; 18:0 ; 18:3Δ^9,12,15; 18:2Δ^9,12
• D. 18:0 ; 18:1Δ⁹ ; 18:2Δ^9,12; 18:3Δ^9,12,15

Answer: (A)

Use the provided shorthand name to draw the structure of the fatty acid myristate (14:0).

Alright. So this practice problem wants us to use the provided shorthand name over here to draw the structure of the fatty acid, muristate. And because muristate is a fatty acid, we know that it's going to have a carboxylic acid group. So we can go ahead and draw that carboxylic acid group over here or this carboxylate group, and then, of course, we know extending off of the carboxylate group there's going to be a hydrocarbon chain of some length. And so if we take a look at the shorthand naming system up here, notice that the very first number is 14, which tells us that there's a total of 14 carbon atoms in the entire fatty acid structure. And we already have one carbon atom as the carboxylic acid carbon. So all we need to do is draw in the other carbon atoms and make sure that there's a total of 14 carbon atoms. So here's carbon number 1. Here's carbon 2. There's 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14 carbon atoms. And so now that we've got the 14 taken care of, looking at the second number, notice that it is a 0, and that tells us that there are 0 double bonds in the hydrocarbon chain. And so really that is it. That means that this is the structure of the fatty acid muristate and that concludes this practice problem, so I'll see you guys in our next video.

Draw the structure of the fatty acid 24:2Δ^5,9. 

Alright. So this practice problem wants us to draw the structure of the fatty acid 24:2 Δ5,9. And so what we need to recall from our previous lesson videos is that 24 is telling us the total number of carbon atoms in the entire fatty acid. The 2 is telling us the total number of double bonds, and then the Δ5,9 is just telling us the position or the location of those double bonds. And so, because this is a fatty acid, we can start off by drawing the carboxylic acid group. So we can go ahead and draw that in here. Here's our carboxylate group, and we know again that there's going to be a hydrocarbon chain branching off. But we know there must be a total number of 24 carbon atoms and 2 double bonds. And the double bonds are going to start at carbon number 5 and carbon number 9, numbering from the carboxylic acid carbon. And so ultimately, what this is going to look like is something like this. Where we have a total number of 24 carbon atoms. So, this would be carbon number 24, and notice that this double bond is 5 carbons away, as indicated right here, and the second double bond is 9 carbons away, as indicated by the 9 here. And really this is the structure and the answer to this problem for drawing this fatty acid, and that concludes this practice. So, I'll see you guys in our next video.

Here’s what students ask on this topic:

What are the different systems of fatty acid nomenclature?

Fatty acid nomenclature includes several systems: the common naming system, the systematic naming system, and the shorthand naming system. The common naming system uses names like oleic acid. The systematic naming system uses names like 9-octadecanoic acid, which provides more detailed structural information. The shorthand naming system, such as 18:1 Δ9, is a concise way to represent fatty acids by indicating the total number of carbon atoms, the number of double bonds, and the positions of the double bonds using the Greek letter delta (Δ). Understanding these systems is crucial for studying fatty acids and their biological roles.

How do you use the shorthand naming system for fatty acids?

The shorthand naming system for fatty acids follows a four-step process: 1) Count the total number of carbon atoms in the fatty acid. 2) Count the total number of double bonds. 3) Separate these two numbers with a colon. 4) If there are double bonds, indicate their positions using the Greek letter delta (Δ) with superscripts. For example, linoleic acid, which has 18 carbon atoms and 2 double bonds at positions 9 and 12, is represented as 18:2 Δ9,12. This system provides a quick and clear way to describe the structure of fatty acids.

What is the common name for the fatty acid with the shorthand notation 18:2 Δ9,12?

The common name for the fatty acid with the shorthand notation 18:2 Δ9,12 is linoleic acid. This notation indicates that the fatty acid has 18 carbon atoms and 2 double bonds located at the 9th and 12th carbon positions. Linoleic acid is an essential fatty acid, meaning it must be obtained through the diet as the human body cannot synthesize it.

Why is it important to understand fatty acid nomenclature?

Understanding fatty acid nomenclature is important because it allows for precise communication about the structure and properties of fatty acids. Different naming systems provide varying levels of detail, which can be crucial for research, nutrition, and understanding metabolic pathways. For instance, knowing the exact structure of a fatty acid can help in studying its role in cell membranes, energy storage, and signaling molecules. Additionally, it aids in identifying essential fatty acids that must be included in the diet.

What is the systematic name for oleic acid?

The systematic name for oleic acid is 9-octadecanoic acid. This name provides detailed information about the structure of the fatty acid, indicating that it has 18 carbon atoms (octadecanoic) and a double bond at the 9th carbon position. Systematic names are useful for conveying specific structural details that are important in scientific research and biochemical studies.