The IUPAC system employs the suffix -one added to the prefix identifying the longest carbon chain of RCOR′ that includes the carbonyl group. The chain is numbered to give the carbonyl group. The chain is numbered to give the carbonyl group the lowest possible number. In the examples given, the names in parentheses correspond to a less systematic nomenclature of ketones by which the R groups each are named separately:

When the doubly bonded oxygen is regarded as a substituent along the parent chain or ring, it is called an oxo group, =O,

By the IUPAC system, the suffix -oic is added to the prefix identifying the hydrocarbon chain that includes the carboxyl carbon:

Situations arise when it is necessary to consider the parent as a one-carbon chain. In such circumstances, RCO2H becomes a substituted carboxylic acid. This variation is met most frequently when RR is a cycloalkyl or aryl group:

The substituent name for −CO2H is carboxy:

For salts of carboxylic acids, the -oic suffix of the acid becomes -oate with the counter ion named as a separate word: