Stearic acid is a saturated acid, and so glyceryl tristearate is a saturated fat. If the fat or oil is saturated, it means that the acid that it was derived from has no carbon-carbon double bonds in its chain. But the truth is that almost everybody calls it (not surprisingly!) by its old name of glyceryl tristearate.
#ESTER FUNCTIONAL GROUP FULL#
The full name for the ester of this with propane-1,2,3-triol is propane-1,2,3-triyl trioctadecanoate.
The acid CH 3(CH 2) 16COOH is called octadecanoic acid, but the old name is still commonly used. In each case, if you want to be strictly accurate, the final oxygen in each row should actually be colour-coded red because it comes from the propane-1,2,3-triol.Īlthough I have shown all the chains in the last structure as the same for simplicity, there is no reason why the three chains in any particular fat or oil molecule have to be the same. Note: The colour coding is still there only to help you to see how the formulae are built up. Now, make the acid chains much longer, and you finally have a fat. If you make an ester of this with ethanoic acid, you could attach three ethanoate groups. Normally, it is drawn with the -OH groups on the right-hand side. Just as with the ethanol in the previous equation, I've drawn this back-to-front to make the next diagrams clearer. The diagram below shows the structure of propane-1,2,3-triol (old name: glycerol). Now let's make the alcohol a bit more complicated by having more than one -OH group. That means that as far as the structure is concerned the oxygen attached to the ethyl group actually ought to be coloured red. When the ester is made, the water that is lost comes from the whole -OH group of the acid and just a single hydrogen from the alcohol. Note: The colour coding refers to the name of the ester and not strictly to the structure. This isn't intended to be a full equation. The diagram shows the relationship between the ethanoic acid, the ethanol and the ester. We'll start with a very, very simple ester like ethyl ethanoate - not something complicated like a fat or oil! This is discussed in detail on another page, but in general terms, the two combine together losing a molecule of water in the process. The causes of the differences in melting points will be discussed further down the page under physical properties.Ī simple introduction to their structuresĮsters can be made from carboxylic acids and alcohols. If the melting points are above room temperature, it will be a solid - a fat. If the melting points are below room temperature, it will be a liquid - an oil. The difference between a fat (like butter) and an oil (like sunflower oil) is simply in the melting points of the mixture of esters they contain. Use the BACK button on your browser to return to this page.Īnimal and vegetable fats and oils are just big complicated esters. Note: You can find more about naming acids and esters by following this link to a different part of this site.
So, for example, CH 3CH 2COOH is propanoic acid, and CH 3CH 2COO is the propanoate group. Notice that the acid is named by counting up the total number of carbon atoms in the chain - including the one in the -COOH group. In each case, be sure that you can see how the names and formulae relate to each other. Take time and care to make sure you understand! Note: In my experience, students starting organic chemistry get more confused about writing names and formulae for esters than for almost anything else - particularly when it comes to less frequently met esters like the ones coming up next. The "ethyl" bit comes from the ethyl group on the end. The "ethanoate" bit comes from ethanoic acid. Notice that the ester is named the opposite way around from the way the formula is written.
In this case, the hydrogen in the -COOH group has been replaced by an ethyl group. The most commonly discussed ester is ethyl ethanoate. This could be an alkyl group like methyl or ethyl, or one containing a benzene ring like phenyl. A carboxylic acid contains the -COOH group, and in an ester the hydrogen in this group is replaced by a hydrocarbon group of some kind. It includes an introduction to more complicated naturally-occurring esters like animal and vegetable fats and oils.Įsters are derived from carboxylic acids. This page explains what esters are and looks at their simple physical properties such as solubility and boiling points.