Constitutional, Configurational and Conformational Isomers:
A. Constitutional Isomers : Isomers in which atoms or group of atoms have different CONNECTIVITY.
Example :
1,1-Dichloroethane and 1,2-Dichloroethane Here the chlorine atom is bonded with different Carbon atoms. It is also known as Structural Isomers.
B. Configurational Isomers : Isomers in which atoms or group of atoms have same CONNECTIVITY but can't be interverted by rotation along bonds or rings.
Example :
cis -1,2-Dichloroethene and trans -1,2-Dichloroethene Here the chlorine atom is bonded with same Carbon atoms , have different orientation of atoms in space but can't be interconverted because of restricted rotation.
C. Conformational Isomer: Isomers in which atoms or group of atoms have same CONNECTIVITY and can be interverted by rotation along bonds or rings. They are not true isomers but have different energy and population at a given temperature.
Example 3 :
Eclipse and Anti form of 1,2-Dichloroethane