Water orbital overlapping

When a metal oxide surface is exposed to water, adsorption of water molecules takes place as shown in Equation 2.1. Cation sites can be considered as Lewis acids and interact with donor molecules like water through a combination of ion-dipole attraction and orbital overlap. Subsequent protonation and deprotonation of the surface hydroxyls produce charged oxide surfaces as shown in Equation 2.2 and Equation 2.3, respectively ... 

It was shown that an enol intermediate was initially formed in the decarboxylation of l -ketoacids and presumably in the decarboxylation of malonic acids. It was found that the rate of decarboxylation of a,a-dimethylacetoacetic acid equalled the rate of disappearance of added bromine or iodine. Yet the reaction was zero order in the halogen . Qualitative rate studies in bicyclic systems support the need for orbital overlap in the transition state between the developing p-orbital on the carbon atom bearing the carboxyl group and the p-orbital on the i -carbonyl carbon atom . It was also demonstrated that the keto, not the enol form, of p ketoacids is responsible for decarboxylation of the free acids from the observa-tion that the rate of decarboxylation of a,a-dimethylacetoacetic acid k cid = 12.1 xlO sec ) is greater than that of acetoacetic acid (fcacw = 2.68x10 sec ) in water at 18 °C. Enolization is not possible for the former acid, but is permissible for the latter. Presumably this conclusion can be extended to malonic acids. 

Because of the very strong dipole moments of these bonds and the very small size of the hydrogen substituents on water, a slight degree of orbital overlap occurs between adjacent water oxygens and hydrogens to give partial covalent bonds known as H-bonds (effectively, can only form with O, N, F). 

The An 5f and An 6d electrons mainly contribute to the covalent bonding between the actinide and actinyl oxygen atoms, as shown in Table 3(a). The orbital overlap populations for both the water molecules and the nitrate groups are found to be smaller. As shown in Table 2, as atomic number changes, the positive effective charge on An slightly decreases and the orbital population of the An 5f electrons increases from 2.94 to 5.14. The increased An 5f electrons... 

An analysis of all the solvent cavities found in the liquid structure shows that the cavity to water radial distribution functions reproduce in detail those found in pure water (19). In a sample as large as ours, most cavities lie outside the second coordination shell. Our transition moment profile, however, contains an orbital overlap term that decreases exponentially with the distance of the cavity from the ion, effectively precluding transitions to cavities located outside the second shell. The cavities between the first and second shells have different structures from those in the bulk Uquid (i.e., those outside the second shell), with four water molecules spanning each cavity. The average kinetic energies of the electron and solvent shift are calculated to be 5.2 eV and 29.7 eV, respectively. 

For d-transition-metal ions, the number of water molecules in the primary coordination sphere (A-zone) is in most cases determined by the strength of orbital overlap between the metal ion and H2O molecules, crystal field stabilization effects, and cationic charge. Other species (e.g., alkaline earths, rare earths) interact with solvent molecules via ion-dipole forces with minimal orbital overlap conhibution to the bonding. Their solvation numbers are determined by a combination of coulombic attraction between cations and water molecules, steric fiictors, and van der Waals repulsion between the bound water molecules. The larger size and high charge of the lanthanides combine with the absence of directed valence effects to produce primary-sphere hydration numbers above eight for these metal ions. 

Orbital overlap models of methane, ammonia, and water. 

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