These differ in the number of carbon atoms and – in the case of unsaturated fatty acids – in the number and position of double bonds. They can be divided into lower, medium and higher acids due to their chain lengths. Those with more than 22-C atoms are also called VLCFAs. Today, this term refers to carboxylic acids with chain-shaped organyl groups.
Natural variants of these acids usually consist of an even number of carbon atoms and are unbranched. Exceptions to this can be found, however, in all empires. Fatty acids with C=C double bonds are called unsaturated variants of these acids. If there are several double bonds, these are usually separated from each other by a methylene group.
A wide variety of these acids are found in the seed oils of the plant kingdom, mostly in the form of triacylglycerides, i.e. esterified with glycerol. Rare fatty acids, esterified in larger percentages in seeds of certain plant families, can illustrate developmental relationships such as petroselinic acid, tariric acid, erucic acid, cyclopentene fatty acids and cyclopropene fatty acids. Some types of bacteria can be distinguished by their fatty acid composition. Essential are the acids that an organism needs but cannot produce itself.