with QM/MM and 77 kJ/mol for the Big-QM calculation. The alternative conformer shows slightly higher barriers (80-95 kJ/mol depending on the functional). We previously discussed the issue regarding a spurious open-shell singlet for 6b and this issue continues along the linear transit, particularly for TPSS. The TPSS calculation for TS 6b-7 is partially collapsed into a close-shell singlet leading to spin populations a magnitude lower, compared to the B3LYP calculation. B3LYP predicts only a small spin-state splitting for the triplet and the open-shell singlet (2-6 kJ/mol depending on the method), so that the barriers are essentially degenerate for both spin states.