Answer:To convert the model of one constitutional isomer to another constitutional isomer one needs to exchange 2 atoms/groups on different atoms.
To convert the model of one stereoisomer to another stereoisomer one needs to exchange 2 atoms/groups bonded to the same carbon.
To convert the model of one conformational isomer to another conformational isomer one only needs to rotate about single bond(s).
Explanation:
Constitutional isomers differ from each other in position of substituents. Hence if we interchange atoms or groups on two different atoms, we get constitutional isomers.
Stereo isomers posses different orientations in space. If two atoms or groups on the same carbon atoms interchange their spatial orientation, we have a different stereoisomer other than the original structure.
Conformers arise by free rotation across single bonds. Different conformers can be created by rotating single bonds.
