Acids - 1

Basic Organic Nomenclature

Carboxylic Acids

Suffix: -oic acid

Prefix: carboxy-

Carboxylic acids contain a functional group, commonly written as -CO₂H or COOH (note: the acidic hydrogen is bold). The carbon atom of the acid (the carbonyl carbon) will be atom number 1 in the numbering scheme. Since it always occurs at the end(s) of the chain of carbon atoms, the number is omitted. In naming the acid, the final -e of the alkane is replaced by -oic acid (note: two words in the name). The general formula for an acid is C_nH_2nO₂. As with several of the other functional groups discussed to this point, the are a large number of acids with common names which will be underlined.

When the -CO₂H group is attached to a ring, the acid is named as a cycloalkanecarboxylic acid (note the -e is retained).
Di-acids occur as well. In this case, since the acid groups must be at each end of the chain, numbers are not necessary to indicate their location.

Examples naming simple acids:

Compound Name	Line Drawing	3D Model
methanoic acid or formic acid
ethanoic acid or acetic acid
propanoic acid
2-methylpropanoic acid
cyclobutanecarboxylic acid
ethanedioic acid * or oxalic acid
propanedioic acid * or malonic acid
butanedioic acid * or succinic acid
hexanedioic acid * or adipic acid

* note: the terminal -e is retained as the dioic begins with a consonant.

Examples naming more complex acids:

Compound Name	Line Drawing
2-hydroxypropanoic acid or lactic acid
5,5-dimethyl-3-oxohexanoic acid
4-amino-6-heptenoic acid

There is an additional, older way to designate the locations of substituents in carboxylic acids which makes use of Greek letters rather than numbers. The labels start at the carbon atom adjacent to the carboxyl carbon, which is labeled the a (alpha) position, the next is the b (beta) position, the next the g (gamma) position, etc. Although the Greek lettering is not IUPAC, it is still common in biology and medicine.

Compound Name	Line Drawing
3-chloropentanoic acid or b-chloropentanoic acid
4-aminobutanoic acid or g-aminobutanoic acid (GABA)

Acids as Substituents:

In more complex molecules with higher priority functional groups, the acid is named as a carboxy- substituent. It is located by numbering the longest chain of carbons (according to the higher priority functional group) and locating the -CO₂H group by this numbering scheme.

Tutorial Quiz: Acids

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