Question

Among the four compounds (i) Acetone (ii) Propanol (iii) Methyl acetate and (iv) Propionic acid, the two that are isomeric are:
(A) Methyl acetate and Acetone
(B) Methyl acetate and Propanol
(C) Propionic acid and Methyl acetate
(D) Propionic acid and Acetone

Answer 1

Hint: First draw the chemical structures of all the given compounds and then assign them a molecular formula. The compounds that have the same molecular formula but show different properties are called isomers.

Complete step by step solution:
Isomers are chemical compounds that have the same molecular formula but show different properties. Isomerism can be divided into many types. First let’s see the structures and molecular formula of the given compounds to find out which two of them are isomers.
(i) Acetone:
Molecular formula: ${C_3}{H_6}O$
Chemical structure: ${H_3}C - CO - C{H_3}$
(ii) Propanol:
Molecular formula: ${C_3}{H_8}O$
Chemical structure: $C{H_3}C{H_2}C{H_2}OH$
(iii) Methyl acetate:
Molecular formula: ${C_3}{H_6}{O_2}$
Chemical structure: $C{H_3}COOC{H_3}$
(iv) Propionic acid:
Molecular formula: ${C_3}{H_6}{O_2}$
Chemical structure: $C{H_3}C{H_2}COOH$
- Looking at the molecular formula of all the given molecules, we can say that Propionic acid and Methyl acetate have the same molecular formulae.
- The chemical structures of both of them are different. So, their properties will also be different.
- We can see that there is an ester group present in methyl acetate. The functional group present in Propionic acid is carboxylic acid group.
- So, this type of isomerism is called functional group isomerism.
- Functional group isomerism is a subcategory of structural isomerism as there is a change in chemical structure in both the isomers.

Therefore we can conclude that the pair of isomers is Propionic acid and methyl acetate and the correct answer is (C).

Note: Note that the first requirement for the compounds to be isomers is the same molecular formula. The isomerism in organic compounds can be divided into two main categories; structural isomerism and stereoisomerism.