Fatty acids are merely carboxylic acids with long hydrocarbon
chains. The hydrocarbon chain length may vary from 10-30 carbons
(most usual is 12-18). The non-polar hydrocarbon alkane chain
is an important counter balance to the polar acid functional
group. In acids with only a few carbons, the acid functional
group dominates and gives the whole molecule a polar character.
However, in fatty acids, the non-polar hydrocarbon chain gives
the molecule a non- polar character.
| Quiz: Which acid (short chain or
fatty) would most likely be soluble in water?
|... in hexane?
Table of Fatty Acids on the left:
The most common fatty acids are listed. Note that there are
two groups of fatty acids--saturated and unsaturated. Recall
that the term unsaturated refers to the presence of one
or more double bonds between carbons as in alkenes.
A saturated fatty acid has all bonding positions between
carbons occupied by hydrogens.
The melting points for the saturated fatty acids follow the
boiling point principle observed
previously. Melting point principle: as the molecular weight
increases, the melting point increases. This observed in
the series lauric (C12), palmitic (C16), stearic (C18).
Room temperature is 25oC, Lauric acid which melts
at 44o is still a solid, while arachidonic acid has
long since melted at -50o, so it is a liquid at room