Enthalpy values proton solvation

Reasonably reliable pATbh+ values for the protonation of weak bases or of weakly basic substrates can be obtained via equation (17), together with m slope parameters that can be used to classify basic molecules as to type, and for an estimate of the solvation requirements of the protonated base. Measurements at temperatures other than 25°C can be handled using equation (22), and enthalpies and entropies for the protonation can be obtained. Protonation-dehydration processes are covered by equation (26). Medium effects on the... 

The different solvation energetics of R and R- will also lead to errors in the bond dissociation enthalpies calculated with equation 16.33. For instance, in the case of phenol, whose interactions with proton-acceptor solvents (like DMSO) are obviously stronger than those for the phenoxy radical, a negative correction should be applied to the value of Z)//°(PhO-H) calculated from equation 16.33 (see also equation 16.32). It is probably unwise to ascribe the 7 kJ mol-1 difference between the electrochemical and the recommended DH° (PhO—R) value to the differential solvation effects. Although this discrepancy is in the correct direction, it lies within the suggested uncertainty of the method. 

The standard free energy for this reaction, AG°, is a measure of the gas-phase acidity of BH (AG°cid) or the gas-phase basicity of B (AG +). The standard enthalpy change for this reaction, AH°, is known as the proton affinity (PA) of the base B (a neutral or anionic species, depending on whether v = 1 or v = 0, respectively). The significance of these values lies in the fact that they are intrinsic in nature, as they are free of solvation contributions6 from both neutral and charged species in a bulk condensed phase. 

Hill T (1960) An introduction to statistical thermodynamics. Addison-Wesley, Reading Tissandier MD et al (1998) The proton s absolute aqueous enthalpy and Gibbs free energy of solvation from cluster-ion solvation data. J Phys Chem A 102(40) 7787-7794 Kelly CP, Cramer CJ, Truhlar DG (2006) Aqueous solvation free energies of ions and ion-water clusters based on an accurate value for the absolute aqueous solvation free energy of the proton. J Phys Chem B 110(32) 16066-16081... 

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