Induced dipole dispersion

The dispersion (London) force is a quantum mechanieal phenomenon. At any instant the electronic distribution in molecule 1 may result in an instantaneous dipole moment, even if 1 is a spherieal nonpolar moleeule. This instantaneous dipole induces a moment in 2, which interacts with the moment in 1. For nonpolar spheres the induced dipole-induced dipole dispersion energy function is... 

Van der Waals forces are very complex and manifest themselves even at distances at which it is unreasonable to assume that orbital interactions can occur. An explanation due to London in terms of the mutual attraction of induced dipoles (dispersion forces) accounts for the long-range behavior. The unoccupied-occupied orbital interactions will be the dominant component of van der Waals forces at short range. See Kauzmann, W., Quantum Chemistry, Academic, New York, 1957, Chapter 13, for a discussion of dispersion forces. 

Induced dipole-induced dipole Dispersion London (1930)... 

Van der Waals interactions are noncovalent and nonelectrostatic forces that result from three separate phenomena permanent dipole-dipole (orientation) interactions, dipole-induced dipole (induction) interactions, and induced dipole-induced dipole (dispersion) interactions [46]. The dispersive interactions are universal, occurring between individual atoms and predominant in clay-water systems [23]. The dispersive van der Waals interactions between individual molecules were extended to macroscopic bodies by Hamaker [46]. Hamaker s work showed that the dispersive (or London) van der Waals forces were significant over larger separation distances for macroscopic bodies than they were for singled molecules. Through a pairwise summation of interacting molecules it can be shown that the potential energy of interaction between flat plates is [7, 23]... 

Molecular polarizability, a, is a measure of the ability of an external electric field, E, to induce a dipole moment, = aE, in the molecule. As such, it can be viewed as contributing to a model for induced dipole (dispersive) interactions in molecules. Because the polarizability is a tensor (matrix) quantity, there is the question of how to represent this in a scalar form. One approach is to use the average of the diagonal components of the polarizability matrix, (a x + otyy + Since the polarizability increases with size (and... 

Atomic repulsion and induced dipole-induced dipole dispersive attraction are typically described by a Lennard-Jones function [16,17] ... 

London Enei Teims. The dipole-induced dipole dispersion energy (i/dd) is given by... 

As an aside, wart removal by liquid nitrogen exploits the same principle. As may be recalled from our discussion of intermolecular forces, the attractions of induced dipoles, dispersion forces, are caused by temporarily uneven distributions in the electron clouds, which produce momentary positive and negative regions. Nitrogen is formed from two nitrogen nuclei bonded together—the electrons have no reason to prefer one nitrogen in the molecule over the other—so dipoles, a permanent separa-... 

It was shown that the folded conformation is favored by ca. 3 kcal/mcd in enthalpy and the entropy change is 3—4 e.u., vdiich is unfavorable to the folded form. The entropy loss on going to the folded conformation is readfly understandable in terms of the freezing out of all motion of the aromatic side chain in the folded form. The intramolecular interaction is not the process accompanyit the release of bound or ordered solvent molecules (hydroj obic interaction). It seems likely that the folded conformation of the aromatic cyclic dipeptides is stabilized by interaction of amide dipole and aromatic induced-dipole, dispersion forces between polarizable rr systems of the amide group and the aromatic ring, and some sbortHranged, h ily directional effects. As a consequence, the intramolecular interaction is characterized by invariant AH and AS with solvent and it is not destroyed even in amide solvent. 

The value of O is determined by the ion-molecule energy surface that has repulsive and attractive parts. The repulsive part is mostly controlled by molecular dimensions as described above. The attractive part comprises induced dipole-induced dipole (dispersion) and charge-induced dipole (polarization) interactions. Both forces, and thus any combination of them, scale with ap that varies by 1.5 orders of magnitude for common gases, increasing in the series He, Ne, Ar, air or N2, CO2 or CH4, SFfi (Table 1.2). 

Gii lu-Ustundag and Temelli [63] reviewed the effect of a co-solvent on the phase behaviom of lipids in SC CO2. They found that physical interactions between the solutes and co-solvent, such as dipole - dipole, dipole - induced dipole or induced dipole - induced dipole (dispersion) interactions and specific interactions such as H-bonding and charge transfer complexes, are important contributors to the co-solvent effect. The use of a cosolvent may also lead to a change in selectivity. The magnitude of the effect of the co-solvent is thus a combination of the solvent, the co-solvent, the solute and the operating conditions. 

Q 11. The following interactions are important in biological self-assembly charge-charge, charge-dipole, dipole-dipole, dipole-induced-dipole, dispersion (London), hydrogen bonding. 

For alkali metal cations—with the one exception of the Li" ion, whose solvation is a mix between electrostatic and covalent interactions—classical electrostatic calculations can account quite well for the observed enthalpies of gas-phase solvation. For instance, hydration can be split up into energy contributions from ion-dipole induced dipole dispersion (E g), and repulsive (E - p) contributions (18) (Table 8). Clearly, the dominant term is the Coulombic attraction between the cation and the water dipoles, which decreases in magnitude as the ion gets bigger. 

A number of electronic descriptors may be cla.ssified as encoding the effects or strengths of intermolecular interactions. The more commonly recognized intermolecular forces arise from the following interactions ion-ion, ion-dipole, dipole-dipole, dipole-induced dipole, dispersion, and hydrogen bonding. Certain electronic descriptors are clearly associated with one or more of these types of interactions. 

The first hint that there are non-covalent interactions between uncharged atoms and molecules came from the observations of van der Waals (1873, 1881). These interactions came to be known as van der Waals forces. The interactions responsible for these became clear with the work of Keesom (1915, 1920, 1921), Debye (1920, 1921) and London (1930) as, respectively, interactions between two permanent dipoles (orientation forces), a permanent dipole and an induced dipole (induction forces) and a fluctuating dip>ole and an induced dipole (dispersion forces). While these three kinds of interaction have different origins, the interaction energies for all three vary as the inverse of the distance raised to the sixth power ... 

Dipole-induced dipole Dispersion (London forces)... 

State the molecular components that contribute to internal energy. Describe and illustrate by example the following intermolecular interactions point charges, dipoles, induced dipoles, dispersion (London) interactions, repulsive forces, and chemical effects. Define a van derWaals force, and relate it to the dipole moment and polarizability of a molecule. Ultimately, you want to be able to relate macroscopic thermodynamic behaviors to their molecular origins as much as possible. 

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