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 positions of –COOH groups are indicated by the arabic numeral before the multiplicative prefix.
What is the IUPAC name of phthalic acid?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Benzene-1,2-dicarboxylic acid
Phthalic acid is a benzene ring with two –COOH groups on adjacent ring carbons, positions 1 and 2. Two carboxyl groups on a ring take the multiplier dicarboxylic acid, with their positions as numbers in front.
NCERT (2026-27 edition):
8.6.1 Nomenclature – “… Some of the carboxylic acids along with their common and IUPAC names are listed in Table 8.3.”
Table 8.3 Names and Structures of Some Carboxylic Acids
