[egilbreth]

Apologies if this has been asked before but could somebody explain what it is about strong σ donation that pushes the eg orbital up in energy and what it is about pi acceptors that lower t2g? I understand on a very basic level that this happens with any pi acceptors or sigma donors, but i am confused as the the reason why it is lowered. Thanks for the *delete me*

[Orcio_87]

Why t2g energy is lowered? When atomic orbitals overleaps there are formed bonding and anti bondig orbitals (bonding orbitals have always lower energy). Similiar - energy of t2g orbitals is lowered as they are part of bonding MO - formed from dxy, dxz, dyz and empty LUMO of pi-acceptor.

In simplified version - they have lower energy as pi-acceptor reduce their electron density.