Repulsion, of like charges

These two experiments make a number of important points. An <7-HMP will not react with an ortho position as long as a para reaction site is available. A p-HMP will react with unoccupied ortho position at about half the rate that it reacts with a substituted para position. This suggests that there is something special about the repulsion between the phenolic hydroxyls. Since the pH was only 8, it is clear that there was ample opportunity for a salted 2-HMP to find and react with an unsalted 2-HMP. Both species were present. On this basis, we cannot invoke repulsion of like-charged ions. According to Jones salted species probably react with unsalted species and this is one reason that reaction rate drops rapidly when PF pH gets much above 9.0 [147]. Yet the phenolic hydroxyl appears to be the cause of the reduced reactivity of the ortho position. Unfortunately, Jones did much of his work in a carbonate buffer. He did not realize the pH-dependent accelerating effects of carbonate on PF condensation. 

The accelerative effect of electrostatic attraction between anions and positively charged substrates and the decelerative repulsion of like charges in the reagents is discussed in Sections I,D, 2,a and b, II,Bj4, and III, A, 2. 

The discussion thus far has focused on the forces between an array of atoms connected together through covalent bonds and their angles. Important interactions occur between atoms not directly bonded together. The theoretical explanation for attractive and repulsive forces for nonbonded atoms i and j is based on electron distributions. The motion of electrons about a nucleus creates instantaneous dipoles. The instantaneous dipoles on atom i induce dipoles of opposite polarity on atom j. The interactions between the instantaneous dipole on atom i with the induced instantaneous dipole on atom j of the two electron clouds of nonbonded atoms are responsible for attractive interactions. The attractive interactions are know as London Dispersion forces,70 which are related to r 6, where r is the distance between nonbonded atoms i and j. As the two electron clouds of nonbonded atoms i and j approach one another, they start to overlap. There is a point where electron-electron and nuclear-nuclear repulsion of like charges overwhelms the London Dispersion forces.33 The repulsive... 

In electrostatic atomization, an electrical potential is applied between a liquid to be atomized and an electrode placed in the spray at a certain distance from liquid discharge nozzle. As a result of the mutual repulsion of like charges accumulated on the liquid surface, the surface becomes unstable and disrupts when the pressure due to the electrostatic forces exceeds the surface tension forces of the liquid. Droplets will be generated continuously if the electrical potential is maintained above a critical value consistent with liquid flow rate. Both DC and AC systems have been employed to provide high electrical potentials for generating fine droplets. Many configurations of electrode have been developed, such as hypodermic needles, sintered bronze filters, and cones. 

Formation of hydrophobic bonds between nonpolar hydrocarbon groups on the drug and those in the receptor site is also common. Although these bonds are not very specific, the interactions take place to exclude water molecules. Repulsive forces that decrease the stability of the drug-receptor interaction include repulsion of like charges and steric hindrance. 

An irradiation-induced expansion could conceivably be caused by the ions, formed as precursors of the radicals, or by thermalized electrons trapped within the polymer. Irradiation induces electrical conductivity in polymers, and this conductivity decays after irradiation is ceased (4, 5). The decay process is accelerated by increased temperature or plasticity of the specimen, presumably by facilitating leakage of the trapped electrons or ions to ground. One might speculate that the sample expands upon irradiation because of the local mutual electrical repulsions of like charges which are trapped in the polymer matrix, and that both increased temperature and plasticizer content diminish this expansion because of charge leakage out of the specimen. It is difficult to prove or disprove this hypothesis. 

At the tip s closest approach to the surface, electrons may flow from the instrument to the surface, or vice versa. According to the laws of classical physics, this flow of electrons is not possible because of the repulsion of like charges (in electron clouds) on the two materials. The laws of quantum mechanics, however, do allow some... 

Is friction electrochemical also At least on moist surfaces, the distance between surface promontories—the protrusions of the metal-metal contacts—is controlled by the repulsion of like charges from ions adsorbed from electrolyte-containing moisture films onto surfaces. Indeed, if a pendulum swings on a fulcrum containing a metal-metal contact, its rate of decay (which is increased by the friction of the contact) maximizes when the interfacial excess electrical charge is a minimum the friction therefore is a maximum (because the metal contacts, unrepelled by charges, are in closer contact). 

If we protonated the oxygen first, there is a problem of the unfavorable electrostatics of having two like charges close to each other. Since we would like to avoid the electrostatic repulsion of like charges, it would be best to deprotonate the nitrogen before protonating the oxygen. 

Figure 13.29 Equilibrium potential. The membrane potential reaches an equilibrium when the driving force due to the concentration gradient is exactly balanced by the opposing force due to the repulsion of like charges.

Oppositely charged species often react more rapidly than neutral species. Ions with the same charge do not react, owing to the repulsion of like charges. In contrast, oppositely charged ions attract one another and are often reactive. 

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