Proton affinities of hydrated molecules

Highlights: • Hydration enthalpies of molecules (M) increase with proton affinities (PA) of M. • There are linear relationships between PAs of hydrated and non-hydrated molecules. • PA of M(H₂O) can be smaller or larger than PA of M. Proton affinities (PA) of non-hydrated, M, and hydrated forms, M(H₂O)_1,2,3, of 20 organic molecules including alcohols, ethers, aldehydes, ketones and amines were calculated by the B3LYP/6-311++G(d,p) method. For homogeneous families, linear correlations were observed between PAs of the M(H₂O)_1,2,3 and the PAs of the non-hydrated molecules. Also, the absolute values of the hydration enthalpies of the protonated molecules decreased linearly with the PAs. The correlation functions predicted that for an amine with PA 2O)) is larger than the corresponding PA, while for an amine with PA > 1100 kJ/mol the PA(M(H₂O)) is smaller than the PA.