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Organic Chemistry Text Book (CHEM 3401 and 3402)

20.1 Nomenclature

As with aldehydes, the carboxyl group must be located at the end of a carbon chain. In the IUPAC system of nomenclature the carboxyl carbon is designated #1, and other substituents are located and named accordingly. The characteristic IUPAC suffix for a carboxyl group is "oic acid", and care must be taken not to confuse this systematic nomenclature with the similar common system. These two nomenclatures are illustrated in the following table, along with their melting and boiling points.



Common 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)2CO2 butyric acid butter (L. butyrum) butanoic acid -5.5 ºC 164 ºC
CH3(CH2)3CO2 valeric acid valerian root pentanoic acid -34.5 ºC 186 ºC
CH3(CH2)4CO2 caproic acid goats (L. caper) hexanoic acid -4.0 ºC 205 ºC
CH3(CH2)5CO2 enanthic acid vines (Gk. oenanthe) heptanoic acid -7.5 ºC 223 ºC
CH3(CH2)6CO2 caprylic acid goats (L. caper) octanoic acid 16.3 ºC 239 ºC
CH3(CH2)7CO2 pelargonic acid pelargonium (an herb) nonanoic acid 12.0 ºC 253 ºC
CH3(CH2)8CO2 capric acid goats (L. caper) decanoic acid 31.0 ºC 219 ºC


Substituted carboxylic acids are named either by the IUPAC system or by common names. If you are uncertain about the IUPAC rules for nomenclature you should review them now. Some common names, the amino acid threonine for example, do not have any systematic origin and must simply be memorized. In other cases, common names make use of the Greek letter notation for carbon atoms near the carboxyl group. Some examples of both nomenclatures are provided below.


Simple dicarboxylic acids having the general formula HO2C–(CH2)n–CO2H (where n = 0 to 5) are known by the common names: Oxalic (n=0), Malonic (n=1), Succinic (n=2), Glutaric (n=3), Adipic (n=4) and Pimelic (n=5) Acids. Common names, such as these can be troublesome to remember, so mnemonic aids, which take the form of a catchy phrase, have been devised. For this group of compounds one such phrase is: "OMSuch Good Apple Pie".