Saturated fatty acids nomenclature

The most common dietary fatty acids are the saturated long-chain fatty acids palmitate (C16) and stearate (C18), the monounsaturated fatty acid oleate (C18 l), and the polyunsaturated essential fatty acid, linoleate (C18 2) (To review fatty acid nomenclature, consult Chapter 5). Animal fat contains principally saturated and monounsaturated long-chain fatty acids, whereas vegetable oils contain linoleate and some longer-chain and polyunsaturated fatty acids. They also contain smaller amounts of branched-chain and odd-chain-length fatty acids. Medium-chain-length fatty acids are present principally in dairy fat (e.g., milk and butter), maternal milk, and vegetable oils. 

A useful convention is to denote fatty acids by the number of carbon atoms and the number of C=C bonds. For example, lauric acid, which has 12 carbon atoms and no C=C bonds, is C12 0. This nomenclature does not specify the position of the C=C bonds, nor whether they are cis or trans. All fats are mixtures of triglycerides (and hence contain a number of different fatty acid residues). The approximate fatty acid composition of some fats is shown in Table 3.4. Butterfat contains a much wider range of fatty acids than the vegetable fats. Coconut oil contains very high levels of saturated fatty acids, particularly lauric acid. 

Lipids with saturated fatty acids are called saturated fats and are commonly solids at room temperature (such as butter and shortening). Unsaturated fats contain one or more double bonds in their carbon—carbon chains. The cis and trans nomenclature we learned for alkenes applies Trans fats have H atoms on the opposite sides of the C=C double bond, and cis fats have H atoms on the same sides of the C=C double bond. Unsaturated fats (such as olive oil and peanut oil) are usually liquid at room temperature and are more often found in plants. For example, the major component (approximately 60 to 80%) of olive oil is oleic acid, as-CH3(CH2)7CH=CH(CH2)7COOH. 

Methyl esters of saturated fatty acids show one stable crystal form. It was originally termed but according to the nomenclature used here it is a )8 -form. The crystal structure of this form in methyl stearate (Aleby and von Sydow, 1960) is shown in Fig. 8.36. Although the forces between the polar groups must be very weak in an ester the molecules are arranged head-to-head in bilayers. The chain packing is the... 

An overview of important fatty acids with an even number of carbon atoms in the molecule is given in Table 3.1. Besides the systematic names derived from the corresponding hydrocarbons, trivial names are also given, and these are used predominately in routine practice, especially in the nomenclature of common fatty acids. In the Hterature, for brevity, various short designations predominate, such as an N M ratio, where N is the number of carbon atoms in the molecule and M the number of double bonds. The most abundant saturated fatty acids in animal and plant tissues... 

The aliphatic chain is referred to as saturated because all carbon atoms are linked to four other atoms (sp carbons in organic chemistry). When a carbon atom is linked to only three other atoms, one of the chemical bond has to be a double bond to respect the valency of 4, which is characteristic of carbon. In this case, the double bond links two carbons and it is noted C=C. The nomenclature used for saturated fatty acids refers to the number of carbon atoms, and to the lack of double bonds correspondingly, palmitic add, which is the saturated fatty acid with 16 carbons, is noted C16 0 (C16 for the carbon number, 0 for the number of double bond). You can train yourself to write the structure of the following fatty acids C9 0, C14 0, and C18 0. A list of biologically saturated fatty acids can be found in Table 1.2. Note that only the limited piece of information found in the first column is useful to draw the chemical structure of all these lipids. 

Saturated fatty acids under systematic nomenclature contain the syllable, -an-, while unsaturated fatty acids contain the syllable. ... 

Figure 1 Fatty-acid structure and nomenclature. (A) Chemical formula and carbon atom numbering system for a 16-carbon saturated fatty acid (16 0). (B) Schematic representation of 16 0. (C) A monounsaturated fatty add, 18 1n-9, showing the double bond nine carbon atoms from the methyl end (carbon 18). (D) The essential n-6 fatty acid 18 2n-6, where the first double bond is found six carbon atoms from the methyl end. The two double bonds are separated by a methylene (-CH2-) group. (E) The essential n-3 fatty acid 18 3n-3, where the first double bond is found three carbon atoms from the methyl end. (F) Phytanic acid, a dietary / -methyl-branched-chain fatty acid (3,7,11,15-tetramethyl 16 0). The melhyl group on carbon 3 prevents this fatty acid from degradation by /3-oxidation. (G) Pristanic acid (2,6,10,14-tetramethyl 15 0) is the product of phytanic acid o-oxidation, in which a single carbon (carbon 1) is lost. The methyl group on carbon 2 does not preclude subsequent degradation by /3-oxidation.

The most frequently used systematic nomenclature names the fatty acid after the hydrocarbon with the same number and arrangement of carbon atoms, with -oic being substituted for the final -e (Genevan system). Thus, saturated acids end in -anoic, eg, octanoic acid, and unsaturated acids with double bonds end in -enoic, eg, octadecenoic acid (oleic acid). 

The nomenclature of carboxylic acids and their derivatives was discussed in Section 7-6. Many carboxylic acids have trivial names and often are referred to as fatty acids. This term applies best to the naturally occurring straight-chain saturated and unsaturated aliphatic acids, which, as esters, are constituents of the fats, waxes, and oils of plants and animals. The most abundant of these fatty acids are palmitic, stearic, oleic, and linoleic acids. 

Table 17.1. Nomenclature of common saturated and unsaturated fatty acids.

In a similar manner to the fatty acids, monohydric, dihydric and phenolic members invariably exists as a mixture of saturated, monoene, diene and triene constituents and rarely in the pure form as one of these four. In the nomenclature of this series a comprehensive system which takes account of the chain length, double bond position and its stereochemistry has not been widely agreed and accepted. Trivial and systematic names thus both abound and because of their dual functional nature as aromatic and acyclic these compounds have remained relatively unclassified. For example, cardanol is a well-known member consisting of saturated, monoene, diene... 

Aliphatic framework molecules most common in organic acids include alkanes (saturated hydrocarbons) and alkenes (unsaturated hydrocarbons). These saturated and unsaturated aliphatic carboxylic acids may be acyclic (straight or branched chains) or alicyclic (aliphatic rings). Acyclic aliphatic monocarboxylic acids are also referred to as fatty acids (Table 1). The first five saturated acids (formic to valeric) of this type are sometimes referred to as short-chain, low-molecular-weight, or volatile fatty acids. Although a nomenclature for these acids has been established by the International Union of Pure and Applied Chemistry (lUPAC), the convention of using the trivial names for the first five saturated acids has remained. Similarly, trivial names are used for the aliphatic dicarboxylic acids (Table 2) that are saturated with two to four carbon atoms (C2-C4) and unsaturated with four carbon atoms (C4). Alicyclic carboxylic acids contain one or more saturated or partially unsaturated rings. These acids most commonly occur... 

---