8.6.1. Nomenclature

Since carboxylic acids are amongst the earliest organic compounds to be isolated from nature, a large number of them are known by their common names. The common names end with the suffix –ic acid and have been derived from Latin or Greek names of their natural sources. For example, formic acid (HCOOH) was first obtained from red ants (Latin: formica means ant), acetic acid (CH3COOH) from vinegar (Latin: acetum, means vinegar), butyric acid (CH3CH2CH2COOH) from rancid butter (Latin: butyrum, means butter).

Carboxylic acids are often named based on their origins, which leads to common names that generally end with ‘-ic acid’. For instance, formic acid comes from ants, acetic acid from vinegar, and butyric acid from rancid butter. These names are influenced by the Latin or Greek roots of the substances from which they were first isolated, making them not only practical but also historically significant.

To relate this to something more everyday, think of how we name fruits based on where they come from. For example, 'apple' is a common name regardless of the variety, much like 'acetic acid' is a common name for vinegar-related compounds. Just as different apples may taste different, different carboxylic acids can have distinct properties yet share a name based on their origin.

In the IUPAC system, aliphatic carboxylic acids are named by replacing the ending –e in the name of the corresponding alkane with –oic acid. In numbering the carbon chain, the carboxylic carbon is numbered one. For naming compounds containing more than one carboxyl group, the alkyl chain leaving carboxyl groups is numbered and the number of carboxyl groups is indicated by adding the multiplicative prefix, dicarboxylic acid, tricarboxylic acid, etc. to the name of parent alkyl chain. The position of –COOH groups are indicated by the arabic numeral before the multiplicative prefix.

According to IUPAC rules, to properly name a carboxylic acid, you start with the name of the corresponding alkane and replace the '-e' ending with '-oic acid'. The carbon atom that bears the carboxyl (-COOH) group is always designated as carbon number one in the chain. When there are multiple carboxyl groups, prefixes like 'di-' or 'tri-' indicate their number. For example, a compound with two carboxyl groups would be named 'dicarboxylic acid'. This naming ensures clarity in communication about the molecule's structure.

Think of naming a family. If a person has multiple siblings, you might say they are the 'first-born', 'second-born', and so on. Similarly, in naming acids, if there are multiple -COOH groups, we specify their counts (like 'dicarboxylic acid') to give more detail about the structure.

Some of the carboxylic acids along with their common and IUPAC names are listed in Table 8.3.

The table presents some well-known carboxylic acids, showing both their common names and their IUPAC names. For instance, formic acid is also known as methanoic acid according to IUPAC nomenclature. This dual naming system reflects both the historical context and the systematic approach to organic chemistry.

This is similar to how some people might call a soda 'pop' or 'soda' depending on where they are from. Just like these regional differences in drink names can lead to confusion, the two naming conventions for carboxylic acids can also give insight into the structural nature of the molecules.

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