Question

Identify the positional isomers among the following:

• A.
• B.
• C.
• D.

Answer 1

Answer: (B), (C)

The correct options are
B
C


Positional isomers have same molecular formula and same carbon skeleton. However, they differ in the position of the functional group. Hence B and C are examples of positional isomers.
In option A, carbon in - CN should be considered as part of the parent chain. Hence the number of carbon in the parent chain for both the structure differs. Hence they are chain isomers.

In option D, they have same number of carbons in the parent chain, fuctional group is different. First one is ketone and other one is aldehyde. Hence they are functional isomers.