Dipoles, water forming

Stimulated by these observations, Odelius et al. [73] performed molecular dynamic (MD) simulations of water adsorption at the surface of muscovite mica. They found that at monolayer coverage, water forms a fully connected two-dimensional hydrogen-bonded network in epitaxy with the mica lattice, which is stable at room temperature. A model of the calculated structure is shown in Figure 26. The icelike monolayer (actually a warped molecular bilayer) corresponds to what we have called phase-I. The model is in line with the observed hexagonal shape of the boundaries between phase-I and phase-II. Another result of the MD simulations is that no free OH bonds stick out of the surface and that on average the dipole moment of the water molecules points downward toward the surface, giving a ferroelectric character to the water bilayer. 

Suhrmann (62) explains the strong increase of the normal photoelectric effect of metals caused by the adsorption of water molecules and also by the molecules of ammonia, by accepting similar coordinate links to function in the chemisorption of these molecules. Dipoles are formed which point with their positive poles away from the surface, thereby decreasing the work function and, consequently, increasing the normal photoelectric effect ... 

As already mentioned in Sec. V,8,b, water molecules may even cause dipoles by forming a coordinate bond with the metal surface, these dipoles working in the same sense as those formed by polarization in the molecules themselves. 

Different dipole liquids, similarly, attract each others molecules by suitable orientation of the dipoles and form stable solutions. We have already mentioned the case of alcohol and water. In ammonia and water, the interaction between neighboring ammonia and water molecules is so strong that they form the ammonium complex, leading to NH4OH... 

The c mechanism concerns two rigid dipoles ji—formed by the left and right water molecules—that reorient harmonically about this bond. 

Colorless, very volatile oily liquid, d 1.86. mp —91.5 bp 82 bpjj7 0. Tromon constant 23.4. The most stable oxide of chlorine. Explodes violently upon concussion or on contact with aflame or iodine. Dipole moment in CCI4 at 20 is 0.72. Does not attack wood or paper. Slowly hydrolyzed by water, forming perchloric acid. 

FIGURE 3.7.7 Surface charge on a protein strand attracts a water dipolar molecule (top). The adsorbed dipole attracts additional dipoles to form a structured organization within the liquid (middle). Additional surface charges on the protein reinforce the external dipole network (bottom). (Redrawn from Pollack, G.H., Cells, Gels, and the Engines of Life A New, Unifying Approach to Cell Function, Ebner and Sons, Seattle, WA, 2001.)... 

In microwave induced organic reactions, the reactions can be carried out in a solvent medium or on a solid support in which no solvent is used. For reactions in a solvent medium, the choice of the solvent is very important. The solvent to be used must have a dipole moment so as to absorb microwaves and a boiling point at least 20-30 °C higher than the desired reaction temperature. An excellent solvent in a domestic microwave oven is N,N-dimethylformamide (DMF) (b.p. 160 °C, 8 = 36.7). The solvent can retain water formed in a reaction, thus, obviating the need for water separation. Some other solvents of choice are given as follows ... 

Static structural calculations for the water cluster anion have revealed the quantum mechanical origin of the binding force for the excess electron and various equilibrium structures. [87, 158, 195, 211, 339] It is now established that the excess electron is bound principally by the dipole field formed by the water molecules. In their elaborate studies on the potential landscape of anion water clusters, Choi and Jordan [87] explored a large number of local minima as well as the transition states on the potential... 

Some ionic compounds are insoluble in water. This observation can be explained by inferring that the ionic bonding within the lattice is stronger than the ion-dipole bonds formed when the ionic solid dissolves and hydrates. The increase in entropy is insufficient to make the process favourable. Insoluble ionic compounds usually have small and highly charged ions and high lattice energies. 

Liu K, Brown M G and Saykally R J 1997 Terahertz laser vibration rotation tunneling spectroscopy and dipole moment of a cage form of the water hexamer J. Phys. Chem. A 101 8995-9010... 

---