The Online Encyclopedia and Dictionary






Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid (or organic acid), often with a long aliphatic tail (long chains), either saturated or unsaturated. Most of the natural fatty acids have an even number of carbon atoms, because they are made up of acetate which has two carbon atoms.

Industrially, fatty acids are produced by the hydrolysis of the ester linkages in a fat or biological oil (both of which are triglycerides), with the removal of glycerol. See oleochemicals.


Saturated fatty acids

Saturated fatty acids do not contain any double bonds or other functional groups along the chain. The term "saturated" refers to hydrogen, in that all carbons (apart from the carboxylic acid [-COOH] group) contain as many hydrogens as possible. In other words, the omega (ω) end contains 3 hydrogens (CH3-) and each carbon within the chain contains 2 hydrogens (-CH2-).

Some saturated fatty acids are:

  • Butyric: CH3(CH2)2COOH
  • Lauric (dodecanoic acid): CH3(CH2)10COOH
  • Myristic (tetradecanoic acid): CH3(CH2)12COOH
  • Palmitic (hexadecanoic acid): CH3(CH2)14COOH
  • Stearic (octadecanoic acid): CH3(CH2)16COOH
  • Arachidic (eicosanoic acid): CH3(CH2)18COOH

Unsaturated fatty acids

Unsaturated fatty acids are of similar form, except that one or more alkene functional groups exist along the chain, substituting singly-bonded


part of the chain with doubly-bonded


portions (this is, with carbons attached with a double bond to another carbon). In most of these, each double bond has 3n carbon atoms after it, for some n, and are all cis bonds.

There are two different ways to make clear where this double bonds are located in the molecule. For example:

Delta-9,12 or Δ9,12 : The double bond are the ninth and twelfth carbon-carbon bond counting from the end of the chain with the carboxyl group.

Omega-3 or Ω-3 : The first double bond is the third carbon-carbon bond counting from the end of the chain most distant from the carboxyl group. The next

  • Alpha Linolenic CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH, is an omega-3 fatty acid.
  • Linoleic acid......CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH, Linoleic and Arachidonic are omega-6 fatty acids.
  • Oleic acid...........CH3(CH2)7CH=CH(CH2)7COOH, oleic and erucic are omega-9 fatty acids .

Stearic and Oleic acid are both 18 C fatty acids. They differ only in that stearic acid is saturated with H, while oleic acid is an unsaturated fatty acid (with two less H than the anterior).


Image.Several fatty acid molecules

Essential fatty acids

Essential fatty acids are polyunsaturated fatty acids that are required in the human diet. This means they cannot be synthesized by the body and must be obtained from food. We can easily make saturated fatty acids and unsaturated fatty acids that have one double bond (monounsaturated fatty acids), but we do not have the proper enzymes to synthesize unsaturated fatty acids that have more than one double bond (polyunsaturated fatty acids). These essential fatty acids are very important to our immune system and to help us regulate our blood pressure, for they are used to make essential compounds, such as prostaglandins.

Trans fatty acids

Main article: Trans fat

A trans fatty acid (commonly shortened to trans fat) is an unsaturated fatty acid molecule that contains a trans double bond between carbon atoms, which makes the molecule less kinked compared to fatty acids with cis double bonds. Research suggests a correlation between diets high in trans fats and diseases like atherosclerosis and coronary heart disease.

Free fatty acids

Fatty acids not bound or attached to other molecules, like triglycerides or phospholipids.

The uncombined fatty acids or free fatty acids may come from the breakdown of a triglyceride into its components (fatty acids and glycerol).

Free fatty acids are an important source of fuel for many tissues since they can yield relatively large quantities of ATP. Typically many cell types can use either glucose or fatty acids for this purpose. However, heart and skeletal muscle prefer fatty acids. On the other hand, brain cannot use fatty acids as a source of fuel, relying instead on glucose, or on ketone bodies produced by the liver from fatty acid metabolism during starvation.


Formic acid and Acetic acid are totally soluble in water and dissociate to form reasonably strong acids. However, as the chain length increases the solubility of the fatty acids decreases very rapidly, and so their pH does not really have a meaning.

They will dissolve in warm ethanol, and can be titrated with sodium hydroxide solution using phenolphthalein as an indicator to a pale pink endpoint.

Autooxidation and rancididty

Fatty acids at room temperature undergo a chemical change known as autoxidation. The fatty acid breaks down into hydrocarbons, ketones, aldehydes, and smaller amounts of epoxides and alcohols. Heavy metals present at low levels in fats and oils promote autoxidation. Fats and oils often are treated with chelating agents such as citric acid.

See also

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