Proton Transfer Equilibrium Constants In The Weak Interaction Is Precisely Calculated

In solution, the interact between the solute and the aqueous solvent is called the aqueous effect. For aqueous solutions, this role is referred to as hydration. Bockris and Conway have defined two types of hydration:(1) Primary hydration refers to those water molecules which are adjacent to the ion and have lost all freedom of independent motion and they always move with the ion. (2) Secondary hydration refers to those water molecules which, although not in the hydration shell, are still held to the ion by electrostatic attraction to a sufficient degree that solvation-dependent properties are affected. For many chemical processes, it is important to know how many solvent molecules in the primary hydration thus can be super molecule in the ion solvation effect.The theoretical study of the pKa. values of acids is a very interesting subject, and it is expected to make up for the insufficiency of experiment. However, aqueous pKa are more difficult to calculate due largely to the effect of the solvent. In order to describe adequately the solute-solvent interaction like hydrogen bonds in the first solvation shell, a combination of the extended clusters-continuum model (ECM) with the polarizable continuum solvation model (PCM) is use to calculate the pKa values of some acids. Explicit water molecules are added to interact with the solute and then the super molecule is embedded in the water. By means of wrapping the acid with water molecules in the solvation shell, this model avoids the complete contact between the solute and the solvent. In this work, we have extended this approach to make a prediction of the pKa values of phenol acid, amino acid, arsenic acid and so on.The great merit of our letter is that we have first outlined our theoretical calculation of the pKa values and then proceeded to illustrate its application to the determination of the hydration numbers. Supra molecules which detem the calculated pKa values closest to the experimental data are the hydration numbers.