Nomenclature of Carboxylic Acids

The IUPAC system of nomenclature assigns a characteristic suffix to these classes. The –e ending is removed from the name of the parent chain and is replaced -anoic acid. Since a carboxylic acid group must always lie at the end of a carbon chain, it is always is given the #1 location position in numbering and it is not necessary to include it in the name.

Many carboxylic acids are called by the common names. These names were chosen by chemists to usually describe a source of where the compound is found. In common names of aldehydes, carbon atoms near the carboxyl group are often designated by Greek letters. The atom adjacent to the carbonyl function is alpha, the next removed is beta and so on.

Formula
Common Name
Source
IUPAC Name
Melting Point
Boiling Point

HCO2H
formic acid
ants (L. formica)
methanoic acid
8.4 ºC
101 ºC

CH3CO2H
acetic acid
vinegar (L. acetum)
ethanoic acid
16.6 ºC
118 ºC

CH3CH2CO2H
propionic acid
milk (Gk. protus prion)
propanoic acid
-20.8 ºC
141 ºC

CH3(CH2)2CO2H
butyric acid
butter (L. butyrum)
butanoic acid
-5.5 ºC
164 ºC

CH3(CH2)3CO2H
valeric acid
valerian root
pentanoic acid
-34.5 ºC
186 ºC

CH3(CH2)4CO2H
caproic acid
goats (L. caper)
hexanoic acid
-4.0 ºC
205 ºC

CH3(CH2)5CO2H
enanthic acid
vines (Gk. oenanthe)
heptanoic acid
-7.5 ºC
223 ºC

CH3(CH2)6CO2H
caprylic acid
goats (L. caper)
octanoic acid
16.3 ºC
239 ºC

CH3(CH2)7CO2H
pelargonic acid
pelargonium (an herb)
nonanoic acid
12.0 ºC
253 ºC

CH3(CH2)8CO2H
capric acid
goats (L. caper)
decanoic acid
31.0 ºC
219 ºC

Example (Common Names Are in Red)

Naming carboxyl groups added to a ring

When a carboxyl group is added to a ring the suffix -carboxylic acid is added to the name of the cyclic compound. The ring carbon attached to the carboxyl group is given the #1 location number.

Naming carboxylates

Salts of carboxylic acids are named by writing the name of the cation followed by the name of the acid with the –ic acid ending replaced by an –ate ending. This is true for both the IUPAC and Common nomenclature systems.

Naming carboxylic acids which contain other functional groups

Carboxylic acids are given the highest nomenclature priority by the IUPAC system. This means that the carboxyl group is given the lowest possible location number and the appropriate nomenclature suffix is included. In the case of molecules containing carboxylic acid and alcohol functional groups the OH is named as a hydroxyl substituent. However, the l in hydroxyl is generally removed.

In the case of molecules containing a carboxylic acid and aldehydes and/or ketones functional groups the carbonyl is named as a “Oxo” substituent.

In the case of molecules containing a carboxylic acid an amine functional group the amine is named as an “amino” substituent.

When carboxylic acids are included with an alkene the following order is followed:

(Location number of the alkene)-(Prefix name for the longest carbon chain minus the -ane ending)-(an –enoic acid ending to indicate the presence of an alkene and carboxylic acid)

Remember that the carboxylic acid has priority so it should get the lowest possible location number. Also, remember that cis/tran or E/Z nomenclature for the alkene needs to be included if necessary.

Naming dicarboxylic acids

For dicarboxylic acids the location numbers for both carboxyl groups are omitted because both functional groups are expected to occupy the ends of the parent chain. The ending –dioic acid is added to the end of the parent chain.