Question

Which of the following compounds exhibit positional isomerism?

• A. 2-butene
• B. 2-butyne
• C. 2-butanol
• D. butanal

Answer 1

Answer: (A), (B), (D)

The correct options are
A 2-butene
B 2-butyne
D butanal

If the position of the functional group is different in two compounds having the same molecular formula and the same functional group then they are position isomers. Given below are structures of 2-butanol and 1- butanol:
Looking at their structures we can see that they
have the same functional group (-OH), only its position is changing. So, they exhibit positional isomerism.
3- butenol have an unsaturated (C=C) bond.

2-butanone has a ketone group (-C=O).

Hence, they cannot be considered as positional isomers.