Potential energy charge-dipole interactions

The ion-dipole interaction lowers the potential energy of the ion in a solvent relative to its value for an ion in a vacuum. It turns out that when Eq. 1 is used to calculate the net potential energy of the interaction between the full charge of an ion and each of the partial charges of a polar molecule, we find... 

Dipole-dipole interaction — refers to intermolecular or intramolecular interaction between molecules or groups having a permanent - dipole moment, ft. The potential energy of the interaction, V, is directly proportional to dipole moments of both dipoles and depends on relative orientation of the - dipoles. For instance, this energy is inversely proportional to the third power of the distance, r, for linearly arranged stationary dipoles of the negative-to-positive directed charges. 

The inner solvation shell itself appears to possess a highly ordered structure. This follows from even the most simple picture one could draw of such a regular arrangement the metal ion attracts the polar solvent molecules and tries to attach them as closely as possible to its surface. On the other hand, the closer the approach of the polar groups, the stronger their mutual repulsion. Since the potential energy of the charge-dipole interaction varies with the square of the reciprocal radius,... 

In the case of ions, the attractive electrostatic potential almost always dominates vibrational quenching at thermal energies, because of the charge-induced dipole force for nonpolar molecules and the even stronger charge-dipole interaction for polar molecules. The case of the above-mentioned N2(n)-He system is an exception, as = 0.017 eV is so small that the minimum of k falls below room temperature, and thus only the increase due to repulsive forces is observed in experiments at elevated energies. 

In MM3 the option exists to compute charge-charge and charge-dipole interaction energies between ions and between ions and polar molecules. The values for the bond dipoles were chosen to reproduce the molecular dipole moments for test molecules. It has been demonstrated that bond dipoles may be derived to reproduce the quantum mechanical molecular electrostatic potential (ESP) and that a dipole model can perform as effectively as the more common partial atomic charge model derived from the same potential.The... 

When a charged solute is dissolved in a solvent with a dipole moment, the electric field associated with the charge exerts a force on the dipole, orienting the oppositely charged end of the dipole toward the charge. For a dipole whose orientation is fixed in space, the potential energy of the interaction varies as the inverse squared distance r between the charge and dipole (Eq. 3.23, where e is the dielectric constant of the solvent and p is the dipole moment ... 

The subscript 1 — 2 in Ui-2 indicates that this is the contribution to the potential energy from the interaction between a monopole (1 charge) and a dipole (2 charges). In the limit that R we can use the binomial series (Eq. A.32) to simplify the difference ... 

The introduction of an >-substituent (CN, Cl, or OH) into a primary n-alkyl chloride considerably enhances the rate of 5 n2 chloride exchange in the gas phase. Reactivity trends suggest that the acceleration is due primarily to through-space solvation of the transition state, especially charge-dipole interactions. Potential-energy surfaces are discussed. In further work by the same group, the translational energy dependence of the rate constants of several gas-phase 5 n2 and carbonyl addition-elimination reactions has been measured by FT-ICR spectroscopy. The results were interpreted by RRKM calculations. 

We have two interaction potential energies between uncharged molecules that vary with distance to the minus sixth power as found in the Lennard-Jones potential. Thus far, none of these interactions accounts for the general attraction between atoms and molecules that are neither charged nor possess a dipole moment. After all, CO and Nj are similarly sized, and have roughly comparable heats of vaporization and hence molecular attraction, although only the former has a dipole moment. 

In Eq. (8-7), which is Coulomb s law, the charges are to be aeeompanied with their signs. Because of the high-order reciprocal dependence on distance in Eqs. (8-11) and (8-12), these quadrupolar interactions are usually negligible. For uncharged polar molecules the dipole-dipole interaction of Eq. (8-10), which has the dependence, is the most important contributor to the electrostatie potential energy. 

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