It is clear from panels (a) and (b), that the distribution of data is skewed and includes outliers, suggesting that the distribution is not normal. This observation is further supported by the results of Shapiro-Wilk and Anderson-Darling normality tests, as well as by calculating the skewness and kurtosis of each dataset ( Explaining the structural differences between each pair of tautomers and how these differences are related to the observed free energy difference is not the primary focus of this study. However, it is generally observed that the energy difference tends to increase if the proton transfer is accompanied by significant changes in electron distribution, resonance, aromaticity, sp 3 /sp 2 conversion (specially in exocyclic bonds), angle/torsional strain, or intramolecular H-bonding, among other factors.