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IV. Nomenclature

         

Systems: Two Abbreviation Systems

After the common names, these are the most frequently used to denote complicated structures.

• The carboxyl-reference system indicates the number of carbons, the number of double bonds, and the positions of the double bonds, counting from the carboxyl carbon (which is numbered 1, as in the IUPAC system). It differs from the IUPAC system in that it uses a number (e.g., 16) to denote chain length instead of a name derived from Greek (e.g., hexadecanoic acid).
• The omega-reference system indicates the number of carbons, the number of double bonds and the position of the double bond closest to the omega carbon, counting from the omega carbon (which is numbered 1 for this purpose). This system is useful in physiological considerations because of the important physiological differences between omega - 3 and omega - 6 fatty acids, and the impossibility to interconvert them in the human body.