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.

What is IUPAC name of the give structure?

Hexa-2,4-dienoic acid

The correct answer is option 3. Hexa-2,4-dienoic acid.

The compound consists of six carbon atoms including the carboxyl carbon thus, it is a derivative of hexanoic acid. The only substituents are two double bonds at the second and fourth carbon considering that the carboxyl carbon is the number one.