Dicarboxylic acids are organic compounds that are substituted
with two carboxylic acid functional groups. In molecular
formulae for dicarboxylic acids, these groups are often written
as HOOC-R-COOH, where R is usually an alkyl, alkenyl, or akynyl
group. Dicarboxylic acids can be used to prepare copolymers such
as nylon, polyurethanes and polyethylene terephthalate. In
general, dicarboxylic acids show the same chemical behaviour and
reactivity as monocarboxylic acids. The ionization of the second
carboxyl group occurs less readily than the first one. This is
because more energy is required to separate a positive hydrogen
ion from the doubly charged anion than from the single charged
anion. A mnemonic to aid in remembering the order of the common
nomenclature for the first six dicarboxylic acids is "Oh my,
such great apple pie!" (oxalic, malonic, succinic, glutaric,
adipic, pimelic). A variant for the first nine adds "Sweet as
sugar!" (suberic, azelaic, sebacic) to the end of the mnemonic.
An additional way of