Repulsion effects

Such attractive forces are relatively weak in comparison to chemisorption energies, and it appears that in chemisorption, repulsion effects may be more important. These can be of two kinds. First, there may be a short-range repulsion affecting nearest-neighbor molecules only, as if the spacing between sites is uncomfortably small for the adsorbate species. A repulsion between the electron clouds of adjacent adsorbed molecules would then give rise to a short-range repulsion, usually represented by an exponential term of the type employed... 

Charge-charge repulsion effects in protolytically activating charged electrophiles certainly play a significant role, which must be overcome. Despite these effeets multidentate protolytic interactions with superacids can take plaee, increasing the electrophilie nature of varied reagents. 

This sequence is not theoretically derivable but based on spectroscopic data. This fact is seldom stressed in textbook accounts, which imply that it refers to the energies of the various orbitals as calculated from the theory. As was mentioned above, the stated sequence refers strictly to the order of filling of orbitals, which may be rationalized by the correct inclusiozi of electronic repulsion effects. 

Foam persistence increases with rise in BW TDS because the bubbles are stabilized by the combined repelling forces of electrical charges at the steam-water interface that result from the high concentration of dissolved salts. The repulsion effect of similar charges prevents bubble thinning, bubble rupture and coalescence mechanisms from taking place. 

Figure 1.49 shows that anions are larger than their parent atoms. The reason can be traced to the increased number of electrons in the valence shell of the anion and the repulsive effects exerted by electrons on one another. The variation in the radii of anions shows the same diagonal trend as that for atoms and cations, with the smallest at the upper right of the periodic table, close to fluorine. 

Each lobe of the d 2 yi orbital interacts predominantly with one point charge. The repulsive effects relate to the electron density within any given orbital so we might describe the interaction in units of lobe repulsion and say that, for the dp. yi orbital, this amounts to 4 = 16 repulsion units (4 squared because electron density oc jF). 

Consider the repulsive effects of the d electrons in a series of MLe complexes as the d configuration of the central metal varies across the transition-metal series. All d electron density will repel the bonding electron density. The effects on the 2g eleetron density will be relatively small, however, as these orbitals largely lie inbetween the bonding regions. On the other hand, electron density directly frustrates the bonding. 

Figure 7-l.The repulsive effects of the d shell on bond lengths. Small increases are expected with occupancy of the t2g subset, large ones with occupancy of the Cg. 

Other studies have also established the preference of the chair conformation with the oxygen in the axial position the rationale for this preference is different from the attractive interaction between the sulfoxide oxygen and the syn-axial hydrogens proposed previously . Rather, a repulsion effect is advocated the equatorial oxygen is squeezed between four vicinal hydrogens, while there are only two corresponding repulsions if it is in the axial position. The correlation between the predicted and observed conformational/orientational preferences in 3,3-dimethylthiane oxide (e.g., equatorial preference in the chair conformation) corroborates this interpretation. The axial preferences of the sulfur-oxygen bond in the thiane oxide is reversed in 3,3-dimethylthiane oxide because of the syn-axial interaction. 4,4-Dimethylthiane oxide, however, maintains a predominance of the axial isomers as deduced from the analysis of NMR data . ... 

CV measurements showed that the reversible eleetrode reaetion of the [Fe(CN)6]" redox eouple was suppressed to some extent by the treatment with the DNA. The addition of the anti-DNA antibody further suppressed the redox reaetion thus decreasing the magnitudes of the CV peak currents. This is most likely caused by a steric hindrance of the bulky protein, which binds to the DNA double strands on the electrode surface, to mainly reduce the effective area of the electrode. The electrostatic repulsive effect may also contribute to the electrode response, since the isoelectric point of mouse IgM is commonly in the range of 4.5 to 7.0. Figure 11 shows the relationship between the decrease in the anodic peak current (A/p ) and the antibody concentration. As seen in this figure, the electrode system responded to the anti-DNA antibody in the concentration range of 1 — 100 nM. For the case of the mouse IgM, which does not interact with double-stranded DNA, the present system gave almost no response. The sensor did not respond to other serum proteins as well (data not shown). 

The molecular parameters for CF13PF4 and (CH3)2PF3 illustrate the influence of the lower electronegativity of the methyl groups and the corresponding increased repulsive effect of the electron pairs of the P-C bonds ... 

Another method that has been applied by our group to the study of enzymatic reactions is the Effective Fragment Potential (EFP) method [19]. The EFP method (developed at Mark Gordon s group at Iowa State University) allows the explicit inclusion of environment effects in quantum chemical calculations. The solvent, which may consist of discrete solvent molecules, protein fragments or other material, is treated explicitly using a model potential that incorporates electrostatics, polarization, and exchange repulsion effects. The solute, which can include some... 

By contrast, relatively hydrophilic particles like those made of pHEMA may maintain colloidal stability even at small size due to the repulsive effects of a water of hydration layer,... 

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