Structure and properties:

A fatty acid consists of a hydrocarbon chain and a terminal carboxylic acid group that is shown in the figure.  Most  fatty  acids  found  in  biology  have  an  even  number  of carbon  atoms  arranged  in an unbranched  chain.  Chain length commonly ranges from 14 to 24 carbon atoms with the most general fatty acids containing 16 or 18 carbon atoms. The saturated fatty acid has all of the carbon atoms in its chain saturated with hydrogen atoms. This provides the common formula CH₃ (CH₂)_nCOOH, where  n  is  an  even  number.  The Monounsaturated fatty acids have one double bond in their structure although polyunsaturated

Figure:  Structures of (a) a saturated fatty acid (palmitate, C16:0); (b) a monounsaturated fatty acid with the double bond in the cis configuration (palmitoleate, C16:1); (c) a monounsaturated fatty acid with the double bond in the trans configuration (C18:1); and (d) a polyunsaturated fatty acid (linoleate, C18:2).

fatty acids  have  two  or  more  double  bonds shown in the figure. The twice bonds in polyunsaturated fatty acids are separated through at least one methylene group.

The characteristics of fatty acids depend on their chain length and the number of double bonds. The Shorter chain length fatty acids have lower melting temperatures than those with longer chains. Unsaturated fatty acids have minor melting temperatures than saturated fatty acids of the same chain length and whilst the corresponding polyunsaturated fatty acids have even lower melting temperatures.