Structure, Properties, and Nomenclature of Carboxylic Acids
Nomenclature of Carboxylic Acids
Aside from their systematic names, many carboxylic acids have trivial names that are often derived from the source in which the particular acid was initially found. Such examples are: formic acid from ants (from the Latin formica), acetic acid from vinegar (from the Latin acetum), propionic acid from milk products (from the Greek pro, the first, and pion, fat), butyric acid from (rancid) butter, valeric acid from valerian roots, and caproic acid from goat's milk (from the Latin caper, goat).
In systematic IUPAC nomenclature, the carboxylic acid's name is derived from the corresponding parent alkane. The longest carbon chain that contains the carboxyl group and the highest possible number of functional groups of the compound is the parent chain. The carboxylic carbon is marked by the position number "1".
Cyclic carboxylic acids that are saturated are called cycloalkane carboxylic acids (Note: The carboxylic carbon cannot be a ring carbon). If the carboxyl group is directly bound to an aromatic ring, the compound's name is derived from benzoic acid. In the case of cyclic compounds, the ring carbon that carries the carboxyl group is marked by the position number "1".
The carboxyl carbon in open-chain carboxylic acids has the position number "1". In trivial nomenclature, small Greek symbols are still often used to indicate the positions regarding the carboxyl group. The carbon that is adjacent to the carboxyl group has the position letter α, while the next carbon has the position letter β, and so on. Amino acids that naturally occur in proteins, for instance, are α-aminocarboxylic acids or (shortly) α-amino acids, respectively.
According to IUPAC nomenclature, dicarboxylic acids are known as alkanedioic acids (the carboxyl carbons are included in the alkane's name). However, trivial names are still largely used. Trivial names of dicarboxylic acids also often derive from the source from which they were initially isolated. Succinic acid (butanedioic acid), for instance, was first found in distillate of succinite. Fumaric acid (trans-butenedioic acid) may have been isolated from the plant Fumaria officinalis which was burnt in the past to drive away evil spirits (from the Latin fumus,smoke).
Maleic acid is relatively less stable than fumaric acid. Upon exposure to light, maleic acid is converted into fumaric acid (view the experimental movie "Isomerization of Maleic Acid into Fumaric Acid").