During the linear transition calculations, we often located different stable conformers due to re-orientation of the water molecules. We thoroughly investigated the relative energies of the different conformers and we denote the different conformers with letters a-l in the Tables in the SI (see Tables S8, S11, S13 and S16). We typically took the lowest energy conformer as reactant for the linear transit, except for 3 where another conformer was better oriented for proton transfer (see Table and). For 3 and 3 red we calculated the internal transfer of the proton from O d to O p (see Fig. and). The transfer leads to stable conformers for both intermediates 3 int and 3 red int that are in principle accessible through a re-orientation. 3 int (in the open-shell singlet state) and 3 red int are 32.4 and 3.3 kJ/mol lower in energy than the conformers 3a or 3i red , respectively. Since 3 int is the lowest energy conformer obtained for 3 (see Table ) we use it to calculate dissociation energies (see below).