Introduction to Carboxylic Acids

Carboxylic acids are compounds that contain the carboxyl group:

These compounds and their common derivatives make up the bulk of organic compounds. Their common derivatives include acid halides:

acid anhydrides:


and amides:

Nomenclature of carboxylic acids

Two systems are used for naming carboxylic acids: the common system and the IUPAC system.

Common names for carboxylic acids are derived from Latin or Greek words that indicate one of their naturally occurring sources. Table 1 lists the common name, structure, source, and etymology for some common carboxylic acids.

TABLE 1 Common Names of Carboxylic Acids

Employ the following steps to derive the IUPAC name for a carboxylic acid:

1. Pick out the longest, continuous chain of carbon atoms that contains the carboxyl group. The parent name for the compound comes from the alkane name for that number of carbon atoms.

2. Change the ‐e ending of the alkane name to ‐oic and add the word “acid.”

3. Locate and name any substituents, labeling their placement by numbering away from the carboxyl group.

Applying these rules gives the following compound the name 2‐ethyl‐4‐methylpentanoic acid.

Naming carboxylic acid salts

Carboxylic acid salts are named in both the common and IUPAC systems by replacing the ‐ic ending of the acid name with ‐ate. For example, CH 3COO K + is potassium acetate or potassium methanoate.

Acidity of carboxylic acids

Carboxylic acids show K a values in the order of 10 −4 to 10 −5 and thus readily react with ordinary aqueous bases such as sodium hydroxide and sodium bicarbonate. This acidity is due to two factors. First, the oxygen atom of the carboxyl group bonded to the hydrogen atom has a partial positive charge on it because of resonance.

Second, the anion that results from the removal of the hydrogen attached to the carboxyl oxygen is resonance stabilized.

Substituting electron withdrawing groups such as halogens on the chain of the R group(s) increases the acidity of the acid. This effect is strongest for α‐substitutions and decreases rapidly as the electron withdrawing group is moved further down the chain.