Question

An aldehyde as well as a ketone can be represented by the same molecular formula, say ${{C}_{3}}{{H}_{6}}O$. Write their structures and name them. State the relation between the two in the language of science.

Answer 1

Hint: Different compounds having the same molecular formula are called isomers. Structural isomers have the same molecular formula but different functional groups are functional isomers.

Complete answer:
The molecular formula given in the question is ${{C}_{3}}{{H}_{6}}O$.
Let us write the structure of aldehyde and ketone with the molecular formula ${{C}_{3}}{{H}_{6}}O$
Structure and chemical name of aldehyde:

Structure and chemical name of ketone:

Thus, the aldehyde and ketone having the same molecular formula ${{C}_{3}}{{H}_{6}}O$ are propanal and propanone (also called acetone), respectively.
These two compounds have the same molecular formula but different functional groups.
Proapnal has an aldehyde functional group. An aldehyde group has one hydrogen (H) and one alkyl (or aryl) group (R) attached to carbonyl carbon.
Propanone has a ketone functional group. In ketone, carbonyl carbon is attached to two same or different alky (or aryl) groups.

Such compounds which can be represented by the same molecular formula but contain different functional groups in their structural formula are known as functional isomers in scientific terms.
Therefore, the relation between propanal and propanone is that they are functional isomers.

Additional Information:
Alcohols and ethers are also functional isomers of each other. They can be represented by the same molecular formula. The general molecular formula for both alcohols and ethers is given as ${{C}_{n}}{{H}_{n+2}}O$. For example, ethanol and methoxymethane can be represented by the same molecular formula ${{C}_{2}}{{H}_{6}}O$ but ethanol is an alcohol while methoxymethane is dimethyl ether.

Note: Note that while writing the IUPAC name of an aldehyde, suffix -al is added while ketone is assigned –one suffix. No more isomers of either aldehyde or ketone can be written for the given molecular formula.