The activation of ethylene on a 4CN Ga site generates a Si-OH group close to Ga. However, second Si-OH group is also present due to the original Ga site creation process (species 2 in Figure ). The close proximity of the two Si-OH groups leads to the possibility of a dehydration step, which gives an oxygen bridged Si pair and a water molecule. The free energy of dehydration is reasonably negative when water is present at low pressures (Pwater = 10 -9 atm, calculations included in Supporting Information). The dehydration step can occur as soon as ethylene is activated, and since the two Si-OH groups are removed, the proton transfer pathway, reforming the original 4CN Ga site, would no longer be viable. As with the 3CN site, β-hydride transfer to ethylene would then lead to C-A mechanism dominated by a Ga-ethyl species (see free energy diagram in Supporting Information).