Water steric number

Figure 9-16 shows the molecular shapes of methane, ammonia, and water, all of which have hydrogen ligands bonded to an inner atom. These molecules have different numbers of ligands, but they all have the same steric number. 

These studies showed that sulfonate groups surrounding the hydronium ion at low X sterically hinder the hydration of fhe hydronium ion. The interfacial structure of sulfonafe pendanfs in fhe membrane was studied by analyzing structural and dynamical parameters such as density of the hydrated polymer radial distribution functions of wafer, ionomers, and protons water coordination numbers of side chains and diffusion coefficients of water and protons. The diffusion coefficienf of wafer agreed well with experimental data for hydronium ions, fhe diffusion coefficienf was found to be 6-10 times smaller than the value for bulk wafer. 

The reduction of a series of 1,3-diimines (76) has been investigated in which the dissolving metal reductions have been carried out both in the presence and absence of proton donors. These compounds exist as a tautomeric mixture of two enaminoimines (77) and (78) and the diimine (76). Reduction by Na-propan-2-ol of five examples (Ar = Ph, 3-tolyl R = Me R = Ph, p-tolyl, cyclohexyl) gave excellent (90-99%) yields of diastereomeric mixtures of three of the four possible fully reduced diamines in which no isomer comprised more than 50% of the reaction mixture. Diamines (79) were not observed, and their absence was attributed to steric factors. On reduction with Li-THF for several hours, followed by quenching with methanol, ethanol or water a number of these tautomeric mixtures (76, Ar = Ph, 3-tolyl R = H, Me, PhCH2, CH2==CH—CH2 R = Ph, 3-tolyl, Me, cyclohexyl) gave saturated ketones, (80) in 70 to 93% yield. ... 

Finally, water, H2O, has steric number 4 with two shared pairs and two unshared pairs on the oxygen atom. VSEPR theory predicts a bent structure, as a subcase of tetrahedral structure, with angles significantly less than the tetrahedral value of 109° due to repulsion between the two unshared pairs and the bonding pairs. Experimentally determined bond angles of 104° verify this prediction. 

When you replace electron pairs with bound atoms, you actually make molecules, and VSEPR can help you figure out what the molecules look like. For example, when you draw the Lewis structure for water, you get two lone pairs of electrons and two bound atoms attached to O (for a total of four things, or a steric number of four). Figure 6-6 shows that an atom with four things bound to it creates a tetrahedron, but when two of those things are invisible, you re left with a bent molecule (or a molecule that looks like a boomerang). 

Calculation of the steric number for methane, ammonia, and water. 

The theory of hydrophobic interaction [70-72] indicates that hydrophobic residues tend to associate with one another so as to minimize the surface area exposed to the aqueous phase and thereby to release a maximum number of structured water molecules. Therefore, the steric fit between the hydrophobic groups may be an important factor for the hydrophobic association. It is reasonable to consider that aromatic hydrophobic groups may undergo tighter hydrophobic self-association because planar aromatic rings would sterically fit with each other to favor the release of structured water. 

Sterically demanding, water-soluble alkylphosphines 6.10 and 6.11 as ligands have been found to have a high activity for the Suzuki coupling of aryl bromides in aqueous solvents (Eq. 6.35).115 Turnover numbers up to 734,000 mmol/mmol Pd have been achieved under such conditions. Glucosamine-based phosphines were found to be efficient ligands for Suzuki cross-coupling reactions in water.116... 

The hemidecarboxylation of sodium phthaiate on reaction with mercuric acetate in boiling water [Eq. (82), X = H] (90) was the first reported thermal decarboxylation. The reaction has been observed for a number of arenes with two adjacent carboxylate groups (1-4,91) and has been named the Pesci reaction (91). Studies of 3-substituted sodium phthalates or of preformed mercuric 3-substituted phthalates have shown that the sterically hindered carboxyl group (the 2-carboxyl) is preferentially eliminated whether X is electron-donating or electron-withdrawing [Eq. (82), X = Me (91), Cl, N02 (91,93), Br (93), or C02H (94)]. A similar conclusion was drawn from the decomposition of mercuric 1,2-naph-thalenedicarboxylate and 3,4-phenanthrenedicarboxylate (91). 

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