Saturated fatty adds chemical structure

Chemical structures of some of these fatty adds are shown in table 14.4. These fatty acids contain 16 (palmitic acid) or 18 carbon atoms with different amounts of unsaturation. Oleic acid (18 1), linoleic acid (18 2), and linolenic acid (18 3) have one, two, and three carbon-carbon double bonds, respectively. Stearic acid is a saturated fatty acid that has 18 carbon atoms and does not contain any carbon-carbon double bonds. The conventional designation of this is 18 0. Another fatty acid found in most vegetable oils is palmitic acid, which contains 16 carbon atoms. Palmitic acid also contains no carbon-carbon double bonds and is designated (16 0). 

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. 

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.

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