Nomenclature:

Fatty acids are named according to the total number of carbon atoms and to the number and position of any twice bonds. The systematic names for fatty acids are  developed  through  adding  'oic  acid'  on  to  the  name  of  the  parent  hydrocarbon. Moreover, as fatty acids are ionized at physiological pH they are commonly written as RCOO^- and have names ending in 'ate' rather than 'oic acid'. A C18 saturated fatty  acid  would  be  known as  octadecanoate and   a  C18  monounsaturated fatty  acid octadecenoate,  and  a C18  fatty  acid  with  two  twice  bonds  octadecadienoate. Yet, several nonsystematic names are still in use.

There is also a shorthand notation to show the number of carbon atoms and the number of any double bonds in the structure.  With 18 carbons a fatty acid

and  no double  bonds  is designated  18:0,  although  one  with  18 carbons  and  two double  bonds  is 18:2. An carbon atoms in fatty acids are numbered from the carboxylic acid residue and so the position of double bonds can be defined using  the  number  of  the  first  carbon  included  in  the  bond  for instance  Δ⁹    shows  a double  bond  among  carbons  9 and  10  of  the  fatty  acid  chain that is also described in the figure.  The configuration  of  the  double  bonds  in  most  unsaturated  fatty  acids  is  cis;  so called because the two hydrogens on the carbon atoms either side of the double bond are on the similar side of the molecule Latin, cis = on this side of. Therefore, the full systematic name of linoleate (Table 1) is cis, cis-Δ⁹, and Δ¹²-octadecadienoate.  In during  the degradation  of fatty  acids some trans-isomers  are establish, where  the hydrogens  on the carbon  atoms either side of the double bond are on opposite sides of the molecule (Latin, trans= across).