Question

Esters are functional group isomers of:
A.Hydroxy aldehydes
B.Ketones
C.Diketones
D.Alkanoic acid

Answer 1

Isomerism is the phenomenon of existence of two or more compounds possessing the same molecular formula but different chemical and physical properties. Functional isomerism is that type of isomerism in which the compounds possess the same molecular formula but the functional groups attached are different.

Complete answer:
Functional isomerism is seen when substances having different functional groups have the same molecular formula. So, to check if functional group isomerism is shown, we must check the compounds of the given functional groups having equal numbers of carbon atoms.
Let us consider the ester ethyl acetate, which has four carbon atoms and is given as $C{H_3}COO{C_2}{H_5}$. Its combined molecular formula can be written as ${C_4}{H_8}{O_2}$
A hydroxyl aldehyde having four carbon atoms is 4- hydroxy butanal and it is given as $HO - {\left( {C{H_2}} \right)_3} - CHO$. Its combined molecular formula can be written as ${C_4}{H_8}{O_2}$. Thus, it is a functional isomer of ester
A ketone having four carbons is butanone and its combined molecular formula is given as ${C_4}{H_8}O$. Thus, it is not a functional isomer of esters.
A diketone having four carbons is 2,3-butanedione and its combined molecular formula is given as ${C_4}{H_8}O$. Thus, it is not a functional isomer of esters.
An alkanoic acid having four carbons is Butanoic acid and its combined molecular formula is given as ${C_4}{H_8}{O_2}$. Thus, it is a functional isomer of ester.

Thus, the correct answers are A and D.

Note:
Isomerism is broadly of two types, that is, structural isomerism or constitutional isomerism, and stereoisomers. Structural isomers are those isomers in which the compounds possessing the same molecular formula differ in their properties due to the difference in the linkage of atoms inside the molecule, i.e., due to a difference in their structures or bonding.
Stereoisomerism is defined as the type of isomerism in which compounds possessing the same molecular formula and same structural formula, differ in their properties due to difference in the arrangement in space of their atoms in the molecule.