and energy with B3LYP/def2-SV(P) are 50.9 and 46.3 kJ/mol, respectively, and thus agree with the proton transfer being generally unfavorable. We additionally performed big-QM calculations and obtain a reaction barrier of 47.1 kJ/mol and a reaction energy of 41.8 kJ/mol, suggesting that the transfer is still unfavorable. Interestingly, the triplet is always lower in energy for the big-QM results (see Fig. ).