Question

In which of the following, functional group isomerism is not possible?

• A. Alcohols
• B. Cyanides
• C. Aldehydes
• D. Alkyl halides

Answer 1

The correct option is D Alkyl halides

Functional group isomerism

Two or more compounds having the same molecular formula but different functional groups are called functional isomers and this phenomenon is termed as functional group isomerism. For example, the molecular formula $C_3{H}_{6}O$ represents an aldehyde and a ketone.

Analysing the options to check functional isomerism

Option $\left(A\right)$

Alcohols and ethers are functional group isomers.

Example, $C{H}_{3}C{H}_{2}OH$ and $C{H}_{3}OC{H}_3$ both have same molecular formula of $C_2{H}_{6}O$

but contains different functional groups.

Option $\left(B\right)$

Aldehyde and ketone shows functional group isomerism.

Example, $C{H}_{3}C{H}_{2}CHO$ and $C{H}_{3}COC{H}_3$ both have same molecular formula of $C_3{H}_{6}O$ but contains different functional groups.

Option $\left(C\right)$

Alkyl halides do not show functional group isomerism, because there isn’t any other functional group with which halides can have same molecular formula.

Option $\left(D\right)$

Cyanides and isocyanides are functional group isomers.

Example, $C{H}_{3}C{H}_{2}CN$ and $C{H}_{3}C{H}_{2}NC$ both have same molecular formula of $C_3{H}_{5}N$ but contains different functional groups.

So, functional group isomerism is not possible in alkyl halides.

Hence, the correct choice is option $\left(C\right).$