The order of overlapping strength of orbitals is given as:
2pπ-2pπ>2pπ-3dπ>2pπ-3pπ>3pπ-3pπ.
The strength of π-bond is directly proportional to the overlapping strength of orbitals because on greater overlapping distance between two nuclei decreases and bond strength increase hence order of π-bond also given as:
2pπ-2pπ>2pπ-3dπ>2pπ-3pπ>3pπ-3pπ.
2pπ-2pπ, π-bonding is stronger than 2pπ-3dπ, π-bonding due to the lower energy gap (n=2) between them.
The importance comparison is in between 2pπ-3dπ and 2pπ-3pπ. The overlapping strength of 2pπ-3dπ is more than 2pπ-3pπ this is due to fact that , the 3d orbitals have two lobes which are more bent than 3p orbitals. That why overlapping strength increase.
