Fatty acids nomenclature, structure

FIGURE B-1 Structures of some fatty acids of neurochemical interest (see also Fig. 3-7 and text). The n minus nomenclature for the position of the double bond(s) is given here. Note that the position of the double bond from the carboxyl end can be indicated by the symbol A, so that linoleic acid may be also be designated as 18 2A9,12. The linolenic acid shown is the a isomer. 

The different phosphoglycerides are often named by placing the constituent attached to the phosphate group after phosphatidyl , e.g. phosphatidyl choline (3-in-phosphatidylcholine or l,2-diacyl-sn-glycero-3-phosphoryl-choline). There are many phosphoglycerides because of the possible variation in the fatty acid chains, and when the full chemical structure is known, it should be used (e.g. l-palmitoyl-2-oleoyl-phosphatidylcholine). Nomenclature that entails the use of the DL system should be avoided. 

Production of phenol and acetone is based on liquid-phase oxidation of isopropylbenzene. Synthetic fatty acids and fatty alcohols for producing surfactants, terephthalic, adipic, and acetic acids used in producing synthetic and artificial fibers, a variety of solvents for the petroleum and coatings industries—these and other important products are obtained by liquid-phase oxidation of organic compounds. Oxidation processes comprise many parallel and sequential macroscopic and unit (or very simple) stages. The active centers in oxidative chain reactions are various free radicals, differing in structure and in reactivity, so that the nomenclature of these labile particles is constantly changing as oxidation processes are clarified by the appearance in the reaction zone of products which are also involved in the complex mechanism of these chemical conversions. 

To facilitate the reader, the nomenclature, structure and properties of the principal fatty acids and of the principal lipid classes are summarized in Appendices 3A, 3B and 3C. The structure and properties of the fat-soluble vitamins, A, D, E and K, are discussed in Chapter 6. 

We introduce here the structures and nomenclature of the fatty acids most commonly found in living organisms. Two types of fatty acid-containing compounds, triacylglycerols and waxes, are described to illustrate the diversity of structure and physical properties in this family of compounds. 

TABLE 10-1 Some Naturally Occurring Fatty Acids Structure, Properties, and Nomenclature... 

Efforts to interpret the forms of isotherms in terms of behaviour at molecular level have tended to concentrate on fatty acids and, to a lesser extent, phospholipids. An understanding of the behaviour of films at the air/water interface in terms of the degree of order in the structure of the film is thus largely limited to these materials. Harkins carried out important early work in the detailed study of the isotherms of fatty acids and this work is summarised in his book The Physical Chemistry of Surface films (72J. The nomenclature that he introduced was derived from an attempt to find an analogy with the behaviour of three-dimensional... 

For personal care applications, the major products in this group are amphoacetates or amphodiacetates , generally based on alkyl hydroxyethyl imidazolines from either a whole coconut fatty acid distribution or a lauric cut. The ampho portion of their name is a convention established by the International Nomenclature Committee for Cosmetic Products (INCI) to indicate that they are derived from imidazoline structures. The INCI nomenclature applied to these materials, amphoacetate and amphodiacetate, is intended to give an indication of the stoichiometry used to produce them, either 1 or 2 mol of sodium chloroacetate is added to each mole of fatty imidazoline. Modern analytical methods have been used to determine the structure of these products and almost all of them are actually monoacetates . The main difference between amphoacetates and ampho diacetates is the composition of the by-products. 

The terms cis and trans, abbreviated c and t, are used widely for double-bond geometry as with only two substituents, there is no ambiguity that requires the systematic Z/E convention. An expansive discussion of fatty acid and lipid nomenclature and structure appears in Akoh and Min (1). 

The nomenclature of starch components has become highly confused through the indiscriminate use of such terms as a and /3-amylose, amylose and amylopectin, amyloamylose and erythroamylose, etc. It does not seem advisable to apply any of these older terms to the new and unique fractions obtained by selective precipitation methods. It is therefore proposed that the term A-fraction be applied to that portion of the starch which is preferentially precipitated by various alcohols or by higher fatty acids, and which exhibits a high affinity for iodine. Correspondingly, the residual non-precipitated portion of the starch, which possesses low iodine affinity, is termed the B-fraction. These designations apply to laboratory-prepared samples, and do not carry any a priori connotations of purity, homogeneity, or structure. 

Table 3.8. The chemical structure of glycerophospholipids. The generic term phosphatidyl- stands for l,2-diacyl-sn-glycero-3-phospho-, in which sn denotes stereospecific numbering (in the D/L nomenclature this corresponds to 2,3-dlacyl-D-glycero-l-phospho-). The OH-groups of the glycerol that are not bound to the head group are esterified to fatty acid.

In the systematic nomenclature of organic compounds the acids of this series are named from the hydrocarbons to which they are related, in a way analogous to that adopted for the fatty acids. For example, acrylic acid, CH2 = CH.COOH, is named propenoic acid. The position of the double bond is indicated by placing before the name of the acid the Greek letter A to which is added a number indicative of the position of the double bond, thus,the substance of the structure,CH3.CH2.CH = CHCH2COOH is called A -hexenoic acid. The after the A indicates that the double bond is between the second and third carbon atom from the carboxyl group. The older names of the acids are usually used in the case, however, of newly described acids, and those of complex structure, the systematic method of naming compounds is employed. 

FIGURE 3.2 (a) The relationship between the three nomenclature notations for fatty acids. Eicosapentaenoic acid (EPA) is shown as an example, (b) Representative structures of the common polyene fatty acids of the n-3 and n-6 families. 

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... 

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