Free Rotation And Restricted Rotation :
Free Rotation
Free rotation is observed in compounds with C-C , C-N, N-N or simply along single bonds without dissociating any bond.
Example 1 :
Ethane
Example 2:
Methylamine
Example 3 :
Hydrazine
Restricted rotation
Restricted rotation is observed in compounds with C=C , C=N, N=N or across a ring system :Any rotation between C=C , C=N, N=N or across a ring system results in dissociation of bond which is not allowed.
Example 4 :
Ethene
Note that any such rotation along C=C will dissociate the bond.
Example 5 :
Cyclopropane
Note that any such rotation along C-C will dissociate the bond.
Example 6 :
cis Azomethane
Note that any such rotation along N=N bond will dissociate the bond.