For reaction II of TaAA9 we were unable to locate an open-shell singlet for 3, although it could be obtained for a conformer of 3, which we here denote 3 ′ . The calculations along reaction II collapse into a closed-shell singlet along the linear transit, the last open-shell singlet energy being 125 kJ/mol (distance between O ox and H OH-Tyr restraint to 1.27 Å) for B3LYP and 84 kJ/mol (distrance restraint to 1.30 Å) for TPSS, cf. Table . This issue has also been observed previously for the TPSS functional with LsAA9. In these cases, we base the discussion on the triplet state.