Instantaneous dipole-induced

The average cloud is spherically synnnetric with respect to the nucleus, but at any instant of time there may be a polarization of charge givmg rise to an instantaneous dipole moment. This instantaneous dipole induces a corresponding instantaneous dipole in the other atom and there is an interaction between the instantaneous dipoles. The dipole of either atom averages to zero over time, but the interaction energy does not because the instantaneous and induced dipoles are correlated and... 

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... 

Both attractive forces and repulsive forces are included in van der Waals interactions. The attractive forces are due primarily to instantaneous dipole-induced dipole interactions that arise because of fluctuations in the electron charge distributions of adjacent nonbonded atoms. Individual van der Waals interactions are weak ones (with stabilization energies of 4.0 to 1.2 kj/mol), but many such interactions occur in a typical protein, and, by sheer force of numbers, they can represent a significant contribution to the stability of a protein. Peter Privalov and George Makhatadze have shown that, for pancreatic ribonuclease A, hen egg white lysozyme, horse heart cytochrome c, and sperm whale myoglobin, van der Waals interactions between tightly packed groups in the interior of the protein are a major contribution to protein stability. 

For a complete quantitative description of the solvent effects on the properties of the distinct diastereoisomers of dendrimers 5 (G = 1) and 6 (G = 1), a multiparameter treatment was used. The reason for using such a treatment is the observation that solute/solvent interactions, responsible for the solvent influence on a given process—such as equilibria, interconversion rates, spectroscopic absorptions, etc.—are caused by a multitude of nonspecific (ion/dipole, dipole/dipole, dipole/induced dipole, instantaneous dipole/induced dipole) and specific (hydrogen bonding, electron pair donor/acceptor, and chaige transfer interactions) intermolecular forces between the solute and solvent molecules. It is then possible to develop individual empirical parameters for each of these distinct and independent interaction mechanisms and combine them into a multiparameter equation such as Eq. 2, "... 

Dispersion forces (instantaneous-dipole - induced-dipole interactions) even in atoms and molecules having no permanent dipole moment, the continuous movement of electrons results, at any instant, in a small dipole moments, which fluctuatingly polarize the electronic system of the neighboring atoms or molecules. This coupling causes the electronic movements to be synchronized in such... 

Dispersion Interactions. Last but not least in the range of solute-solvent electrostatic interactions come the dispersion forces which depend on the polarizabilities of the molecules. Any atom or molecule—non-polar or polar—has a small fluctuating dipole moment as the electrons move around the nuclei. These instantaneous dipoles induce dipole moments in all other polarizable molecules, so that the interaction energy is proportional to the product of the average polarizabilities aM and as of the solute and solvent molecules... 

At any one instant, a nonpolar molecule like CH3CH3 can have an uneven distribution of electrons—an instantaneous dipole.This dipole can induce a dipole in a nearby molecule.This instantaneous dipole-induced dipole interaction is the weakest of all. 

A. They can arise due to instantaneous dipole-induced dipole... 

Instantaneous dipole / induced dipole At any specific moment the electron cloud is not necesarily symetrical, this instantaneous dipole then induces a dipole in another molecule and they are attracted, this is the weakest of all molecular interactions. 

In terms of intermolecular interactions, the boiling point represents the temperature at which molecules possess enough thermal energy to overcome the various intermolecular attractions binding the molecules into the liquid (e.g. hydrogen bonds, dipole-dipole attraction, instantaneous-dipole induced-dipole attractions). Therefore the boiling point is also an index of the strength of intermolecular attractive forces. 

The first term, r , arises from the instantaneous dipole/induced dipole energy of the interaction. If this coefficient, Ca, is adjusted empirically, then the higher terms may be ignored. 

Instantaneous dipoles induce dipoles in other nonpolar molecules. 

The van der Waals radius determines the shortest distance over which intermolecu-iar forces operate it is aiways larger than the covalent radius. Intermolecular forces are much weaker than bonding (intramolecular) forces. Ion-dipole forces occur between ions and poiar molecules. Dipole-dipole forces occur between oppositely charged poles on polar molecules. Hydrogen bonding, a special type of dipole-dipole force, occurs when H bonded to N, O, or F is attracted to the lone pair of N, O, or F in another molecule. Electron clouds can be distorted (polarized) in an electric field. Dispersion (London) forces are instantaneous dipole-induced dipole forces that occur among all particles and increase with number of electrons (molar mass). Molecular shape determines the extent of contact between molecules and can be a factor in the strength of dispersion forces. 

Instantaneous dipole-induced dipoie (London force) attraction between two nonpolar molecules that results from the interaction of an instantaneous dipole in one with an induced dipole in the other. This is the weakest force of all, but there can be a large number of them. These last three are called van der Waals forces. 

Fig. 2.7. London altraclive force is caused by instantaneous dipoles induced in all atoms.

London dispersionforces (dispersion forces) Intermolecular forces resulting from the small, instantaneous dipoles (induced dipoles) that occur because of the varying positions of the electrons during their motion about the nuclei. 

Dispersion forces, sometimes called London forces, are common to all molecules. They are also referred to as instantaneous dipole-induced dipole forces. This rather awkward sounding term points us to the origin of these forces, so let s consider each part of the name separately. To begin with, recall that a dipole exists whenever we have two oppositely charged points or objects separated by some distance. 

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