Protons hydration

Indeed, because most hydrogen atoms in liquid water are hydrogen-bonded to a neighboring water molecule, this protonic hydration is an instantaneous process and the ion products of water are and OH ... 

These special features are explained by an interaction between the proton and one of the water molecules, which is not merely electrostatic but also covalent. This yields a new chemical species, the hydroxonium ion, HjO. The existence of such ions was demonstrated in the gas phase by mass spectrometry and in the solid phase by X-ray diffraction and nuclear magnetic resonance. The H -H20 bond has an energy of 712kJ/mol, which is almost two-thirds of the total proton hydration energy. 

The sequential reactions 4.1 and 4.2 represent the self-dissociation of water as the exchange of a proton between water molecules, where hydration of the proton according to reaction 4.2 is the driving force for its separation (reaction 4.1) although the proton hydration is not limited to one H20 (hydration number 1), nor is the occurrence of unhydrated OH ion realistic, the overall reaction 4.3 is generally written as the simplest form to show the principle of proton acidity. 

During the course of the work, we also conducted further studies of the reactions of proton hydrates with CH3COCH3 and CH3COOCH3. The reaction mechanisms were found to change from proton transfer to ligand switching and ultimately to an association process, which would be equivalent to adsorption in the case of bulk systems. 

One could also expect protons to cross the interface causing protonation (hydration) of the oxide ... 

In such a case, chemical interaction with the solution can take place. This is likely to be primarily the protonation (hydration) reaction leading to formation of some soluble complex ions which diffuse toward the bulk of the solution. Hence, this produces a mechanism for dissolving and thinning the oxide layer, and the rate of this process should be some function of the hydrogen ion... 

When the intensity ratios are measured for a variety of buffers, and the values are plotted vs. pH, the values approach 0.8 at low pH (Figure 6), the same as the fraction of 3 existing in solution as the protonated, hydrated form (cf. Figure 4). This could mean that the residual 1600 cm 1 band seen at low pH is due to protonated, unhydrated 3 on the surface. 

V vs. SCE. Curve is mole fraction of protonated/hydrated species present in solution. 

The combination of the acidic proton hydration 3-32 and the basic proton hydration 3-34 leads to the ionic dissociation of water molecule as shown in Eqn. 3-36 ... 

In general, the acidic and basic proton hydration processes may occur simultaneously giving the same proton level for both the acidic and the basic protons. In pure liquid water where WHgo- = Woh- io electroneutrality, the proton level is obtained from Eqns. 3-39 and 3-40 as shown in Eqn. 3-41 ... 

Smirnov, I.V. 2007. Anomalous effects in extraction of lanthanides and actinides with bidentate neutral organophosphorous extractants. Role of proton hydrate solvates. Radiochemistry 47(1) 44—54. 

Solvation of both e and H2O leads to a situation where only solvated protons hydrated electrons e and hydroxyl radicals... 

These include information on the dynamics of proton hydration. 

A series of p-aryloxy- and p-alkoxyphenylnitrenium ions have been generated in aqueous solutions by photolysis of the parent azides, whereupon the resulting nitrenes are protonated. Hydration of these cations at the para position leads via hemiacetal or halohydrin intermediates to quinone imines, which finally hydrolyse to the ultimate quinone products. In flash-photolysis studies of these reactions it was shown that nitrenium ion hydration occurs on the ps timescale, hemiacetal or halohydrin breakdown on the MS timescale, and the final imine hydrolysis over minutes. 

Theoretical studies on protonated hydrates (PH) are illustrative of the progress realized in theoretical chemistry over several decades. The evolution of such studies is presented. The main methods used (quantum chemistry, Monte Carlo or Molecular Dynamics calculations...) and the problems encountered are briefly recalled. Some of the results obtained are commented. 

The first theoretical papers, mainly related with explaining the abnormal mobility of water (2-4), are based on simple models. Protonated hydrates were, in fact, considered within a more general treatment of liquids or solids. The first quantum chemistry calculations appeared in the sixties (5,6) and were concerned with H30+. Its geometry was not yet well known and a planar (5) or a pyramidal structure (6) has been proposed. As we shall discuss below, the determination of the geometry of the oxonium ion was not trivial. Experimental determinations of the structure appeared only in 1980, and then in 1985 (7). 

Recently, a new category of methods, the cavity model, has been proposed to account for the solvent effect. Molecules or supermolecules are embedded in a cavity surrounded by a dielectric continuum, the solvent being represented by its static dielectric constant. The molecules (supermolecules) polarize the continuum. As a consequence this creates an electrostatic potential in the cavity. This reaction potential interacts with the molecules (supermolecules). This effect can be taken into account through an interaction operator. The usual SCF scheme is modified into a SCRF (self consistent reaction field) scheme, and similar modifications can be implemented beyond the SCF level. Several studies based on this category of methods have been published on protonated hydrates. They account for the solvent effect on the filling of the first solvation shell (53, 69), the charges (69, 76) and the energy barrier to proton transfer (53, 76). 

The quantum chemistry studies published on protonated hydrates at the end of the last decade reveal two interesting features. One is a strong need for more information about many-body contributions, closely related to the use of analytical potential in modellisation techniques. The other is the sudden break-through of the DFT method in this field. These two points deserve a particular attention and are developed in the next two sections. 

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