Fatty acid number notation

Lipid numbers take the form C D, where C is the number of carbon atoms in the fatty acid and D is the number of double bonds in the fatty acid. This notation can be ambiguous, as some different fatty acids can have the same numbers. Consequently, when ambiguity exists this notation is usually paired with either a A or n x term. 

Scheme 12.1 Unsaturated fatty acids (X — H), fatty acid methyl esters (X = CH j) and related epoxy derivatives. Short notation C xx y, where xx is the number of carbon atoms of the fatty acid and y is the number of unsaturations A", where n is the position of the unsaturation.

There is also a shorthand notation to show the number of carbon atoms and the position of any double bonds in the structure. A fatty acid with 18 carbons and no double bonds is designated 18 0, while one with 18 carbons and two double bonds is 18 2. The carbon atoms in fatty acids are numbered from the carboxylic acid residue, and so the position of double bonds can be described using the number of the first carbon involved in the bond (e.g. A9 shows a... 

A number notation used widely for indicating the structure of a fatty acid is shown under the names of the fatty acids in Example 6.3. To the left of the colon is shown the number of C atoms in the acid to the right, the number of double bonds. The position of the double bond is shown by a superscript A followed by the number of carbons between the double bond and the end of the chain, with the carbon of the carboxylic acid group being called 1. 

The number notations, systematic name, and trivial name, respectively, for three more fatty acids are ... 

Individuals who are not fats and oils chemists may benefit from the following orientation. Polyunsamrated fatty acids is abbreviated as PUFA. Essential fatty acids (EFA) are required by the host animal but are not synthesized and are available only through the diet. The notation Cl8 indicates a fatty acid chain, 18 carbons long. C18 0 and C18 3 identify the number of unsaturated ( double ) bonds. C18 0 represents a completely saturated fatty acid, 18 carbons long, in this case, stearic acid. C18 3 represents a fatty acid, 18 carbons long and with 3 unsaturated sites, but does not indicate the location of the double bonds. 

Fatty acids are identified in a shorthand notation by the number of carbon atoms... 

The important attributes of a fatty acid are its carbon chain length, the number of double bonds present and their positions, which can be represented by a simple notation scheme. For example, oleic acid can be represented by c/s-18 1 co9, where cis refers to the stereochemistry about the C=C bond (see Fig. 2.2b and Box 2.3), 18 is the number of C atoms, the number of double bonds (1) is given after the colon, and the number following co is the position of the double bond from the opposite end to the acid group. As double bonds in polyunsaturated acids are usually conjugated (see Section 2.1.2), it is only necessary to give the position of the first double bond because all others follow on alternate carbon atoms. Hence... 

Draw the general chemical formula of a fatty acid and be able to use standard notation for representing the number of carbons and double bonds in a fatty acid chain. 

Give the systematic name and number notation for the following fatty acids that have commonly used trivial names ... 

Fatty acids and acylglycerols. Fatty acids are carboxylic acids with a long hydrocarbon chain and a varying degree of unsaturation. They are designated by a special notation that includes the number of carbons, followed by a number that indicates the degree of unsaturation. For example, octadecenoic (oleic) acid (1) is denoted as 18 1 and hexadecanoic acid (2) as 16 0. 

More than 500 different fatty acids have been isolated from various cells and tissues. Given in Table 19.1 are common names and structural formulas for the most abundant of them. The number of carbons in a fatty acid and the number of carbon-carbon double bonds in its hydrocarbon chain are shown by two numbers separated by a colon. In this notation, linoleic acid, for example, is designated as an 18 2 fatty acid its 18-carbon chain contains two carbon-carbon double bonds. 

It is probable that our ancestors of several million years ago developed the characteristics leading to our modem biochemistry by eating animal fats (Crawford and Marsh, 1989 Sinclair and O Dea, 1990 O Dea, 1991). At first glance this should simplify discussion of animal fats, as shown by the basic fatty acids of Table 10.1. A popular shorthand notation is used to indicate the stmctures of common fatty acids. In the format x yn-z, x is the chain length or number of carbons in the chain, y is the number of methylene-interrupted cis ethylenic bonds and z is the inclusive number of carbon atoms from the terminal methyl group to the center of the nearest bond. As few as six fatty acids appear to adequately describe animal depot fats. Those fats listed are dominated by two fatty acids, 16 0 (palmitic) and 18 1 (oleic) add. Although tropical seed oils may be rich in C12-C18 saturated fatty adds (Elson, 1992), temperate oilseeds are rich in oleic acid and tend to include quantities of two fatty acids more unsaturated than oleic, especially 18 2n-6 (linoleic), and sometimes 18 3n-3 (linolenic). Even the original rapeseed (Brassica sp.) oil, with up to 50% of 22 ln-9 (emdc) acid usually had approximately 20% 18 2/1-6 and 10% 18 3/i-3 adds (Ackman 1983, 1990). 

A shorthand notation shows the number of carbon atoms in the molecule, followed by a colon and the number of double bonds. The position of the first double bond from the methyl group of the fatty acid is shown by n- or CO- (the CD-carbon is the furthest from the a-carbon, which is the one to which the carboxyl group is attached CD (omega) is the last letter of the Greek alphabet). 

In addition, categorising polyunsaturated fatty acids according to the position of the double bond away from the terminal methyl group is common in biological documents. The nomenclature n-x (or a>-x) means that the first double bond is located on carbon number x counting from the terminal methyl group. The omega notation is common in popular nutritional hterature. Linoleic acid is an example of a polyunsaturated fatty add of the n-6 series (3-8). A short notation for linoleic acid is 18 2n-6 (or 18 2 )-6). Similarly, we come across fatty acids of n-3 (or a>-3) series (3-9). 

New notation for number of carbon atoms and double bonds in a fatty acid is added. 

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