Question

Which of the following is not true regarding the structural isomerism?

• A. The bonds between the molecules and the relative positions remain the same.
• B. Sometimes a new atom may be introduced, so the number of atoms might change.
• C. The functional group is always the same.
• D. The functional group might change.

Answer 1

Answer: (A), (B), (C)

The correct options are
A The bonds between the molecules and the relative positions remain the same.
B Sometimes a new atom may be introduced, so the number of atoms might change.
C The functional group is always the same.

Structural isomerism arises when molecules have the same molecular formula but the spatial arrangement of their atoms is different.

Consider the following two molecules for example.



Here the molecular formula is $C_4{H}_{1}0$ in both cases but clearly, the structures are different.
So, it is easy to see that the bonds between the atoms and the relative positions are always subject to change in the structural isomerism. They remain the same in stereoisomers though.
The number of atoms always remains the same in all isomers and the functional group can vary which gives rise to functional isomerism.