NOMENCLATURE
The aliphatic carboxylic acids are commonly known by their initial names, which have been derived from the source of the particular acid.
Examples:
- HCOOH Formic acid [Latin: Fermica = ant]
- CH3COOH Acetic acid [Latin: acetum = Vinegar]
- CH3–CH2–COOH Propionic acid [Greek: Proton = First; Pion = Fat]
- CH3(CH2)2COOH Butyric acid [Latin: Butyrum = Butter]
- CH3(CH2)3COOH Valeric acid
- CH3(CH2)14COOH Palmitic acid
- CH3(CH2)16COOH Stearic acid
Alternative system of nomenclature is naming the acids as the derivatives of acetic acids. The only exception being formic acid.
Example:
CH3 – CH2 – COOH Methyl acetic acid
(CH3)3C – COOH Trimethyl acetic acid
According to the IUPAC system of nomenclature, the suffix of the monocarboxylic acid is ‘oic acid’, which is added to the name of the alkane corresponding to the longest carbon chain containing the carboxyl group, e.g.
HCOOH methanoic acid
CH3 – CH2 – CH2 – COOH butanoic acid
The positions of side-chains (or substituents) are indicated by numbers, the numbering to be started from the side of the carboxyl group.
Naming of Acyl Groups, Acid Chlorides and Anhydrides:
The group obtained from a carboxylic acid by the removal of the hydroxyl portion is known as an acyl group. The name of an acyl group is created by changing the – ic acid at the end of the name of the carboxylic acid to –yl, examples:
Acid chlorides are named systematically as acyl chlorides.
An acid anhydride is named by substituting anhydride for acid in the name of the acid from which it is derived.
Naming of Salts and Esters:
The name of the cation (in the case of a salt) or the name of the organic group attached to the oxygen of the carboxyl group (in the case of an ester) precedes the name of the acid.
Naming of Amides and Imides:
The names of amides are formed by replacing –oic acid (or –ic acid for common names) by amide or –carboxylic acid by carboxamide.
If the nitrogen atom of the amide has any alkyl groups as substitutents, the name of the amide is prefixed by the capital letter N; to indicate substitution on nitrogen, followed by the name(s) of alkyl group(s).
If the substituent on the nitrogen atom of an amide is a phenyl group, the ending for the name of the carboxylic acid is changed to anilide
Some dicarboxylic acids form cylic amides in which two acyl groups are bonded to the nitrogen atom. The suffix imide is given to such compounds.
Illustration 1. Give the IUPAC names and common names of the following compounds
| (i) |  |
ii) |  |
| (iii) |  |
iv) |  |
Solution: IUPAC Name General name
(i) Ethanedioic acid Oxalic acid
(ii) Butanedioic acid Succinic acid
(iii) 2-Hydroxy propanoic acid Lactic acid
(iv) 2, 3 Dihydroxybutanedioic acid Tartaric acid
Illustration 2. Which is not a hydroxy acid?
(A) lactic acid (B) tartaric acid
(C) citric acid (D) succinic acid
Solution: (D)
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