Fatty acid

     Fatty acids are carboxylic acids with carbon chain length ranging from 10 to 30 atoms.

Basic Chemistry

     In fatty acids hydrophobic long carbon chain dominates in chemical properties the hydrophilic carboxyl group and gives the whole molecule hydrophobic character (Ophardt, 2003).

      Naturally occurring fatty acids usually contain an even number of carbon atoms. The most common are 16 and 18 atoms long. The carbon skeleton is unbranched with a few exceptions. Longer carbon chain promotes stronger intermolecular interactions. This means that fatty acids with longer carbon chain have higher melting points (see Table 1). Some fatty acids contain double bonds in their alkyl chain. These are predominately in cis configuration, which results in "kinks" in the chain shape, in contrast with straight saturated acids. Effectively, straight acid fatty acids can "pack" closer together and therefore have higher melting points due to stronger molecular interactions (see Table 1) (Berg et al, 2002).  

Table 1 (Ophardt, 2003), (Berg et al, 2002)

Trivial Name	Trivial carboxylate name	Formal Name	Designation	Melting Point (°C)
Lauric Acid	lauroyl	dodecanoyl	12:0	+44
Myristic Acid	myristoyl	tetradecanoyl	14:0	+54
Palmitic Acid	palmitoyl	hexadecanoyl	16:0	+63
Stearic Acid	stearoyl	octadecanoyl	18:0	+70
Oleic Acid	oleoyl	cis-9-octadecenoyl	18:1c Δ9	+13
Linoleic Acid	linoleoyl	di-cis-9,12-octadecadienoyl	18:2cc Δ9,12	-5
Linolenic Acid	linolenoyl	all-cis-9, 12,15-octadecatrienoyl	18:3ccc Δ9,12,15	-11
Arachidonic Acid	arachidonoyl	all-cis-5,8,11,14-eicosatetraenoyl	20:4cccc Δ5,8,11,14	-50

Nomenclature

     Systematic names for fatty acids are derived from their parent hydrocarbon names by adding the suffix -oic. Thereby, the fatty acid with 16 carbon atoms is called hexadecanoic acid. A monounsaturated fatty acid with 16 carbon atoms is called hexadecenoic acid. Fatty acids with 2 and 3 double bonds are called hexadecadienoic and hexadecatrienoic respectively. Trivial names are also commonly used (see Table 1). Greek letter Δ followed by a superscript number denotes the position of a double bond. Also, because at physiological pH fatty acids form ions, it is appropriate to reffer to them accordingly (see Table 1) (Berg et al, 2002).  

References    

     Charles E. Ophardt, 2003. Virtual Chembook. [online] Available at <http://www.elmhurst.edu/~chm/vchembook/551fattyacids.html> [Accessed 11 January 2011]

     Jeremy M. Berg, John L. Tymoczko, Lubert Stryer, 2002. Biochemistry. 5th ed. New York: W. H. Freeman and Company