In order for low spin splitting to occur, the energy cost of placing an electron into an already singly occupied orbital must be less than the cost of placing the additional electron into an e g orbital at an energy cost of Δ. As noted above, e g refers to the d z and d x - y which are higher in energy than the t 2g in octahedral complexes. If the energy required to pair two electrons is greater than Δ, the energy cost of placing an electron in an e g, high spin splitting occurs.