25.3. Functional Groups http://www.ck12.org
Methanal, also known as formaldehyde, was once commonly used as a biological preservative for dead animals.
In recent years, formaldehyde has been shown to be a carcinogen, so safer alternatives are often used instead.
Aldehydes are also used in the production of resins and plastics. The simplest ketone, propanone, is commonly
called acetone. Acetone is a common organic solvent that was once used in most nail polish removers, but it has
largely been replaced by other solvents. Aldehydes and ketones are fairly volatile compounds and are commonly
found in perfumes and flavorings. For example, the odor and flavor of cinnamon is a result of an aldehyde called
cinnamaldehyde. The aroma of raspberries is provided by a ketone simply called raspberry ketone.
Carboxylic Acids
Organic acids such as acetic acid all contain a functional group called acarboxyl group.
The carboxyl group consists of a carbonyl group (C=O) in which the carbon is also bonded to a hydroxyl (−OH)
group. Acarboxylic acidis an organic compound that contains the carboxyl functional group. The general formula
for a carboxylic acid can be abbreviated as –COOH. In addition to the carbonyl oxygen and the hydroxyl group,
the carbon atom of the carboxyl group may be attached to a hydrogen atom or to a carbon chain. To name a simple
carboxylic acid, find the longest continuous chain that contains the carboxyl group and name the parent chain. Then,
change the –eat the end of the name of the alkane to –oic acid. Because a carboxyl group must be at the end of a
chain, no numbers are needed to indicate its position. If other substituents are present, number the parent chain so
that the carboxyl carbon atom is first. Two examples are shown below.
Properties of Carboxylic Acids
Carboxylic acids are all weak acids. In aqueous solution, the O−H bond of the hydroxyl group can break, yielding
a negative carboxylate ion and the hydrogen ion.