Van der Waals effect

Influence of van der Waals Effects and Other Weak Forces on Peptide Interactions in Reversed-Phase Chromatography... 

To apply these ideas to coagulation phenomena, we must consider what happens to these distributions of potential when two similar surfaces approach one another (Section 11.7). To study coagulation phenomena, we need to compare the electrostatic effects of particle approach with the van der Waals effects discussed in the last chapter. This is done in terms of potential energy curves as discussed in Section 10.2. As we move through the chapter, our interest shifts from potential (volts) to potential energy (joules). It is important to keep track of the difference between the two as the development progresses. 

Incremental Approach to Noncovalent Interactions Coulomb and van der Waals Effects in Organic Ion Pairs. 

The 0.2-ppm downfield shift of the rerr-butyl protons in ort/io-di-tert-butylbenzene with respect to the terf-butyl resonances in the meta and para isomers has been attributed to a van der Waals effect. Possibly the most dramatic example is in the partial cage compound 3-9, in... 

Close approach of the solute and the solvent can distort the shape of the electron cloud around a proton and deshield it, even when both components are nonpolar. Such a phenomenon (cTw) is analogous to the van der Waals effect on the chemical shift. The magnitude is rarely more than 0.1 ppm. If chemical shifts are measured from the resonance of an internal standard, the contribution from ctw should affect the solute and the standard similarly. Chemical shifts so measured should be largely independent of ctw-... 

Force-field calculations have given the atomic co-ordinates for 3a-hydroxy-5a-androstan-17-one ( androsterone ) with about the same accuracy as X-ray measurements, the errors being no greater than 0.1 A. The value of this method lies partly in its speed (10 minutes of IBM 360 computer time) and partly in the fact that no crystal is required. Variations of energy with conformation can also be computed. The authors stress the likely dangers in using Dreiding models, which may differ markedly in shape from actual molecules because they fail to simulate torsional and van der Waals effects. 

A more realistic situation is thus one for a sufficiently thick film that van der Waals effects can still be neglected but both gravity and capillary effects are present. In this case,. v < 0 still, if the film is on top of the solid substrate, and in fact the disturbance decays more rapidly than if either of these effects is absent. In fact, according to our linear theory, the leveling rate is proportional to... 

If the interaction involves charged particles the pressure broadening is called the Stark effect, while collisions with uncharged particles is due to the van der Waals effect, and collisions between the same kind of atoms gives rise to the Holtzmark or resonance broadening effect. 

In a later paper, Kromhout and Linder have reexamined the problem of calculating 0 and present a theory for calculating the London -van der Waals effect on nuclear magnetic shielding of closed shell atoms [205]. They also attempt to extend the theory to polyatomic molecules and derive two explicit expressions for the factor B in Eq. (3.24). The value of B is found to be proportional to the polarizability, a, of the atom under study, the total diamagnetic shielding constant for the closed shell atom and a function of the ionization... 

In especially the continuum-type models for the van der Waals effects, it is implicit that the values of the observed medium effects are dependent on the nature of both the solute and the solvent. This expectation is clearly born out in a statistical factor analysis study by Weiner and Malinowski [206] of proton shifts of non-polar solutes in a variety of solvents. If the van der Waals term for a solute i in a solvent k is written as t a con-... 

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