Fig. and Fig. ). In both conformers, the Cu coordination sphere is best described as a square pyramid with similar distortion. However, 6b* shows a distance between O oxyl and the C4-hydrogen of 3.37 Å, while the different conformation in 6b results in a distance between O oxyl and H C4 of 2.08 Å. The oxyl species in 6b is therefore perfectly set up for the HAA from the substrate. Thus, although the conformer 6b* is slightly more stable than 6b (by ∼10 kJ/mol for both functionals), we mainly focus on the latter here. We report both the formation of 6b* (Fig. , Fig. and Tab. S4) as well as the results for reaction 6b*→7* (Fig. , Fig. and Tab. S10) in the SI. The results do not change qualitatively and we also note that the small difference in energy between 6b and 6b* indicates that both intermediates are likely to be found during catalytic turnover. The H-transfer from the substrate is predicted to be thermodynamically favorable for the triplet state. The reaction energy is -37 kJ/mol (-29 kJ/mol with TPSS). The Big-QM calculation aligns well with the QM/MM energy, yielding a reaction energy of -32 kJ/mol.