Nomenclature
Several different systems of nomenclature are used for fatty acids. The following table describes the most common systems.
| System | Example | Explanation |
|---|---|---|
| Trivial nomenclature | Palmitoleic acid | Trivial names (or common names) are non-systematic historical names, which are the most frequent naming system used in literature. Most common fatty acids have trivial names in addition to their systematic names (see below). These names frequently do not follow any pattern, but they are concise and often unambiguous. |
| Systematic nomenclature | (9Z)-octadecenoic acid | Systematic names (or IUPAC names) derive from the standard IUPAC Rules for the Nomenclature of Organic Chemistry, published in 1979, along with a recommendation published specifically for lipids in 1977. Counting begins from the carboxylic acid end. Double bonds are labelled with cis-/trans- notation or E-/Z- notation, where appropriate. This notation is generally more verbose than common nomenclature, but has the advantage of being more technically clear and descriptive. |
| Δx nomenclature | cis,cis-Δ9,Δ12 octadecadienoic acid | In Δx (or delta-x) nomenclature, each double bond is indicated by Δx, where the double bond is located on the xth carbon–carbon bond, counting from the carboxylic acid end. Each double bond is preceded by a cis- or trans- prefix, indicating the conformation of the molecule around the bond. For example, linoleic acid is designated "cis-Δ9, cis-Δ12 octadecadienoic acid". This nomenclature has the advantage of being less verbose than systematic nomenclature, but is no more technically clear or descriptive. |
| n−x nomenclature | n−3 | n−x (n minus x; also ω−x or omega-x) nomenclature both provides names for individual compounds and classifies them by their likely biosynthetic properties in animals. A double bond is located on the xth carbon–carbon bond, counting from the terminal methyl carbon (designated as n or ω) toward the carbonyl carbon. For example, α-Linolenic acid is classified as a n−3 or omega-3 fatty acid, and so it is likely to share a biosynthetic pathway with other compounds of this type. The ω−x, omega-x, or "omega" notation is common in popular nutritional literature, but IUPAC has deprecated it in favor of n−x notation in technical documents. The most commonly researched fatty acid biosynthetic pathways are n−3 and n−6, which are hypothesized to decrease or increase, respectively, inflammation. |
| Lipid numbers | 18:3 18:3ω6 18:3, cis,cis,cis-Δ9,Δ12,Δ15 |
Lipid numbers take the form C:D, where C is the number of carbon atoms in the fatty acid and D is the number of double bonds in the fatty acid (if more than one, the double bonds are assumed to be methylene interrupted, i.e., at intervals of 3 carbon atoms along the chain). This notation can be ambiguous, as some different fatty acids can have the same numbers. Consequently, when ambiguity exists this notation is usually paired with either a Δx or n−x term. |
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