[BenjaGuz]

I'm kind of new here, and english is not my native language, sorry if I get some writing errors.
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α-Linolenic Acid (ALA)


Linolenic Acid (LA)


My doubt about this Lipid Acid, is why is it called as "Alpha Linolenic Acid" referring to the "Alpha", while his cousin in law "Linolenic Acid" is practically the same, but without the cis double bond on the fifteenth carbon.
Does this "Alpha" means something referred to that cis  double bond in writing down chemical structures? Or it's just a kind of chemical agreement?

Thanks

[Enthalpy]

Welcome here! 

Several fatty acids bear nearly the same name, unfortunately...
Linoleic (one "n") has TWO double bonds
Alpha-linoleNic (two "n") has THREE double bonds in positions 9, 12, 15 (hence near the omega end!)
Gamma-linoleNic (two "n") has THREE double bonds in positions 6, 9, 12

http://en.wikipedia.org/wiki/Fatty_acid
http://en.wikipedia.org/wiki/Linoleic_acid
http://en.wikipedia.org/wiki/Alpha-linolenic_acid
http://en.wikipedia.org/wiki/Gamma-Linolenic_acid

English isn't my native language neither, so other people shall bear with both of us

[BenjaGuz]

Thanks for the orthographic correction, I'll correct it, but I don't have my answer yet my friend, now that you put Gamma-linolenic acid in game, I would like to know what does "Alpha" and "Gamma" words should mean. Does they mean something with the position of the double bonds o something? or they are just words that were putted there because someone "wanted to"?

[Babcock_Hall]

The alpha (α) and gamma (γ) are clearly isomers of each other.  I think that the prefixes predate attempts to systematize fatty acid nomenclature and may be arbitrary.  There is an old thread on this, but I have not checked all of the links:  http://www.chemicalforums.com/index.php?topic=36798.0