α- (alpha-) linolenic acid (ALA) is an omega-3
(omega minus three) fatty acid.
This means that it has a
double bond between carbon atoms
starting at the
Ω (omega) -3 position, which is 3 carbons back from the end opposite to the
-COOH group (which is normally counted as the α (alpha) carbon - number 1).
In fact it has
3 double bonds, so it can be called
polyunsaturated. Each of these double bonds is in the
cis form, rather than the
trans form, so the
single hydrogen atoms are on the same side of the bond.
Alternative names for the molecule are (9Z,12Z,15Z)-octadeca-9,12,15-trienoic acid, all-cis-9,12,15-octadecatrienoic acid or 18:3 (n-3).
Alpha-linolenic acid is an 18-carbon polyunsaturated fatty acid and it is said to be nutritionally essential as the body cannot synthesise it, but it can be converted into other useful unsaturated fatty acids.
It is said that the consumption of omega-3 fatty acids may reduce the risk of coronary heart disease, and also may possibly have anti-cancer effects.
Alpha-linolenic acid is especially common in various plant seeds e.g. flax seed and oils derived from them.
Gamma-linolenic acid is another isomer of this compound, with different properties.
Linolenic acid is the main component in linseed oil, used for maintaining and toughening up wooden articles like cricket bats, and in putty, used traditionally in glazing windows. In these cases the double-bonded molecular structure causes oxidation and polymerisation on exposure to air, producing more solid products.