Question

IUPAC name of valeric acid is _______.
(A) Propanoic acid
(B) Butanoic acid
(C) Ethanoic acid
(D) Pentanoic acid

Answer 1

The word ‘valero’ refers to a compound having five carbon atoms. In addition to that in any compound having ‘valero’ in its name, the main functional group is present at the terminal atom of the five carbon chain.

Complete answer:
We first need to identify what is valeric acid and how its structure looks like to identify its IUPAC name.
The word ‘valero’ means having a structure of a straight chain of five carbons in chemistry. So, valeric acid is a molecule which has a straight chain of 5 carbons and one of the terminal carbon atoms is carbon of carboxylic acid group. So, its structure would be,

Now, we will name it according to IUPAC nomenclature.
The main functional group in this compound is carboxylic acid. So, we will need to find the longest chain of carbon atoms in this compound such that the carbon of carboxylic acid is involved in the counting. There is only a chain of five carbons.
We will start numbering from the carbon of carboxylic acid as there is a rule that we must start numbering the chain of carbons in such a way that the carbon atom having high priority should be given the lowest number.
Here, the first carbon is of carboxylic acid and the chain is of five carbons so, we will use -oic acid suffix and name the compound.
So, the name will be, 1-Pentanoic acid or Pentan-1-oic acid.
So, correct answer is (D) Pentanoic acid

Additional Information:
- There are certain prefixes in organic chemistry that have certain meanings. Such as aceto shows two carbons. ’propio’ shows the presence of three carbons. Same way ‘butyro’, ‘valero’ and ‘capro’ shows presence of 4, 5 and 6 carbon atoms respectively in any compound.

Note: Do not consider that carboxylic acid group is attached to a five carbon atom chain in the valeric acid because that will result in a total six carbon compound and that is not valeric acid. The only 1-pentanoic acid isomer of this compound is known as valeric acid. No other isomers of this compound are known as valeric acid.