3.13 Fatty Acids

Aliphatic carboxylic acids with 3 or more unbranched carbons are called fatty acids, since they can be obtained by breaking down fats and oils from plant or animal sources, and they have physical and chemical properties that resemble these fats and oils. The fatty acids that occur in living organisms can have very long chains, in excess of 20 carbons. Some of these are saturated, some monounsaturated, and some are polyunsaturated, and many of the unsaturated fatty acids have their own common names that I won't attempt to list out.

There are also aryl carboxylic acids such as benzoic acid C6H5CO2H, as well as oddities like cyclohexyl carboxylic acid C6H11CO2H.

Carboxylic acids are known for their odors. Formic, acetic, propionic, and butyric acids are all miscible with water, and have odors varying from vinegar-like for the first two to cheesy and vomit-like for butyric acid. Valeric through pelargonic acids are oily liquids that are slightly to sparingly soluble in water, with odors that range from cheesy to rancid. Larger molecular weight acids starting with capric acid are waxy insoluble solids. Caproic acid smells rancid; lauric acid smells waxy-metallic; myristic acid smells waxy, and larger molecule acids starting with heptadecanoic acid are odorless when pure.

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