for the deprotonation reaction. We developed this FF by matching the well-known monethanolamine deprotonation equilibrium constant value at 298.15 K, which involved adjusting the GAFF oxygen atom partial charge. We are thereby able to predict the pK a of a diverse set of 77 amines at 298.15 K and all other temperatures by the appropriate combination of ideal-gas and residual chemical potential values for the deprotonation reactions. The predictions at 298.15 K show an absolute average deviation (AAD) with respect to experimental values of less than 0.72 pK a unit (our previous study 23 on 29 amines incorporating the Tissandier value of the proton hydration free energy achieved an AAD of 0.73 pK a units at 298.15 K). This is equivalent to an absolute error of ≈ 4 kJ in the reaction free energy at 298.15 K, which is within so-called "chemical accuracy" of 1 kcal•mol -1 .