A quick introduction to fatty acids

(A) This is the structure of stearic acid, an 18-carbon saturated fatty acid. The normal numbering system, starting with the carboxylic acid, is shown in blue. The carbons and oxygens of the carboxylic acid functional group are red. (B) This is the structure of oleic acid, an 18-carbon unsaturated fat. The carbons of the alkene functional group, the site of unsaturation, are in the rounded rectangle. Since there is only one double bond, oleic acid is an example of a monounsaturated fatty acid. This also illustrates the omega labeling system, with the numbers in blue indicating the number from omega-1, the carbon farthest from the carboxylic acid group, to the first carbon of the double bond. Since the first carbon in a double bond is carbon 9, oleic acid is an omega-9 fatty acid. (C) This is linoleic acid. To simplify larger molecules scientists often use line-angle drawings. In these drawings, every line is a bond and every bend is a carbon atom. Most hydrogen atoms are not shown, and it is assumed each carbon has enough hydrogens so that each carbon has four bonds. Since linoleic acid has more than one double bond (it has two), it is a polyunsaturated fatty acid. The omega numbering system has been applied to this molecule. Here, counting in from the omega end, the first double bond encountered is on carbon 6, so this is an example of an omega-6 fatty acid.