Question

Note: Consider the following four compounds for answering the question

$I$
$II$

$III$

$IV$

Which of the following pairs are not functional group isomers?

• A. II and IV
• B. I and IV
• C. II and III
• D. I and II

Answer 1

Answer: (B), (C)

II and III

Functional isomers :

Isomers which have different functional groups are called functional isomers.

Analysing options

Among the given four compounds:

$\left(A\right):$ $II$ and $III$ have ketone functional group but at different positions. So, they are position isomers and not functional isomers.

$\left(B\right):II$ and $IV$ are ketone and aldehyde respectively (different functional groups). So, they are functional isomers.

$\left(C\right):$ Molecules $I$ and $IV$ are aldehydes and so have same functional group. So, they are not functional isomers.

$\left(D\right):$ Molecule $I$ is an aldehyde but molecule $II$ is ketone. So, they are functional isomers.

Hence, options $\left(A\right)$ and $\left(C\right)$ are correct.