Carboxylic Acids

There are also complex aldehydes and ketones in hormonal structures seen in animals. These include hormones like testosterone, progesterone, and cortisone—all complex ketone structures.

CARBOXYLIC ACIDS

The carboxylic acid has a carbonyl group and a hydroxyl group together, making a COOH functional group. This leads to increased activity compared to aldehydes and ketones. Because of this reactivity, it is considered a distinct functional group. The parent chain remains the same but the ending becomes “anoic acid”. The carboxylic acid group is always at the end of the chain, leading to this being the number one carbon atom. Similar to aldehydes, the carbon atoms are considered not by numbers but by the alpha, beta, gamma system set up by the Greeks.

There are many common names of carboxylic acids that you should memorize. This includes the following:

• Formic acid—this goes by the IUPAC name of methanoic acid

• Acetic acid—this has the IUPAC name of ethanoic acid and comes from vinegar

• Propionic acid—this has the IUPAC name of propanoic acid and comes from milk

• Butyric acid—this has the IUPAC name of butanoic acid and comes from butter

• Valeric acid—this has the IUPAC name of pentanoic acid and comes from valerian root

• Caproic acid—this has the IUPAC name of hexanoic acid and comes from goats

• Enanthic acid—this has the IUPAC name of heptanoic acid

• Caprylic acid—this has the IUPAC name of octanoic acid

• Pelargonic acid—this has the IUPAC name of nonanoic acid

• Capric acid—this has the IUPAC name of decanoic acid and comes from goats

Carboxylic acids can be seen in a ring structure, in which it simply has the suffix “carboxylic acid” attached to it. Wherever it attaches to the ring, the carbon atom is given the number one designation. There can be cis and trans molecules. Figure 46 shows the structure of some cyclic carboxylic acids:

Figure 46.

The salts of carboxylic acids are called carboxylates. This is the case with common endings and IUPAC endings so that sodium acetate becomes the salt of acetic acid. It is made with the loss of the hydrogen ion, the presence of a negative charge, and the addition of a salt.

Carboxylic acids are given the highest nomenclature priority using the IUPAC system. The carboxyl group is given the lowest possible number with alcohol groups called “hydroxy” groups in the nomenclature setting. This would lead to things like 3hydroxypentanoic acid, which is a five-carbon chain, a COOH at the end, and a hydroxyl group on the third carbon atom. If an amine functional group is present, this is called an amino group, leading to molecules like 2-aminobutyric acid, also called 2aminobutanoic acid. The addition of an alkene leads to an “enoic acid”, such as 3pentenoic acid, which has a double bond at the 3-position (remember that cis and trans or E and Z are necessary for alkenes).

Of course, there can be carboxylic acid functional groups on both ends of the molecule, leading to a dicarboxylic acid. This is then referred to as a “dioic acid”, such as butanedioic acid—a four carbon dicarboxylic acid.