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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).

Tab.1
Trivial names and systematic names (in brackets) of selected carboxylic acids.
Fig.1

Formic acid (methanoic acid)

Fig.2

Acetic acid (ethanoic acid)

Fig.3

Propionic acid (propanoic acid)

Fig.4

Butyric acid (butanoic acid)

Fig.5

Valeric acid (pentanoic acid)

Fig.6

Caproic acid (hexanoic acid)

Fig.7

Acrylic acid (propenoic acid)

Fig.8

Valerian flowers

Fig.9

Benzoic acid

Carboxylic acids - Examples

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".

Fig.10
Functional groups' order of precedence in the nomenclature of organic compounds.

NOTE: Do not mix up this order of precedence with the CIP priority! It only means that, for instance, an amino acid is not called a carboxy amine.

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".

Tab.2
Examples of carboxylic acid's systematic IUPAC nomenclature.
Fig.11
Fig.12
Fig.13
Fig.14

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.

Tab.3
Naming of positions in carboxylic acids.
Systematic nomenclature
Fig.15
Trivial nomenclature
Fig.16

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).

Tab.4
Dicarboxylic acids.
Fig.17

Oxalic acid (ethanedioic acid)

Fig.18

Malonic acid (propanedioic acid)

Fig.19

Succinic acid (butanedioic acid)

Fig.20

Glutaric acid (pentanedioic acid)

Fig.21

Adipic acid (hexanedioic acid)

Fig.22

Maleic acid (cis-2-butenedioic acid)

Fig.23

Fumaric acid (trans-2-butenedioic acid)

Dicarboxylic acids - Examples

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").

Isomerization of Maleic Acid into Fumaric Acid

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