Inductive forces

An attractive force between a molecule with a permanent dipole moment and a nonpolar molecule comes about when the first molecule induces a dipole moment in the second. Such attractive forces are called inductive forces. The induced moment obeys the following relation  

For the field strength E at a distance r from a point charge q, we have 

At the position of the polarisable molecule, one obtains for the relative orientation assumed in Fig. 2.2 a field strength due to the first dipole equal to 

If we denote the induced moment as p2 = Pind. we obtain with Eqns. (2.3) and (2.5) the attractive force between the molecule with a permanent dipole moment pi and the polarisable molecule  

The forces calculated from Eq. (2.9) are called inductive forces. An important aspect is their strong dependence on the distance, corresponding to r . Furthermore, they are proportional to the polarisability of the molecules. 

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Note the r dependence of these tenns the charge-indiiced-dipole interaction varies as r, the dipole-indiiced-dipole as and the quadnipole-mduced-dipole as In general, the interaction between a pennanent 2 -pole moment and an induced I -pole moment varies as + L + l) gQ enough r, only the leading tenn is important, with higher tenns increasing in importance as r decreases. The induction forces are clearly nonadditive because a third molecule will induce another set of miiltipole moments in tlie first two, and these will then interact. Induction forces are almost never dominant since dispersion is usually more important. 

Kreek H and Meath W J 1969 Charge-overlap effects. Dispersion and induction forces J. Chem. Phys. 50 2289... 

A polar molecule can also induce a dipole on a neighbouring molecule that possesses no permanent dipole. The resultant intermolecular attraction between the permanent and the induced dipole is spoken of as the induction force. Its magnitude is small and independent of temperature. 

Induction forces, the so-called Debye forces ind> occur in the interaction between a permanent dipole of a solute or a polar solvent and an induced dipole in another compound. They are weak and appear during the analysis of the nonpolar polarized compounds, such as those with multiple... 

It is important to know the influence of the physicochemical parameters of the mobile phase (dipole moment, dielectric constant, and refractive index) on solvent strength and selectivity. The main interactions in planar chromatography between the molecules of the mobile phases and those of solutes are caused by dispersion forces related to the refractive index, dipole-dipole forces related to the dipole moment, induction forces related to a permanent dipole and an induced one, hydrogen bonding, and dielectric interactions related to the dielectric constant. Solvent strength depends mainly on the dipole moment of the mobile phase, whereas the solvent selectivity depends on the dielectric constant of the mobile phase. 

The physical forces involved in the hydrogen bond must include electrostatic and inductive forces in addition to London dispersion forces... 

Whereas the electrostatic forces arising from permanent moments can be attractive or repulsive (depending on orientation), the induction forces are intrinsically attractive. In the large-R limit, these interactions are generally negligible (i.e., of... 

Many different types of forces arise from molecule-molecule interaction. They may be electrostatic forces between permanent dipoles, induction forces between a permanent dipole and induced dipoles, or dispersion forces between non-polar molecules, etc. (Prausnitz, U2)). Forces involved in molecule-molecule interaction are known to be short-range in nature. 

Lipophilicity is a molecular property experimentally determined as the logarithm of the partition coefficient (log P) of a solute between two non-miscible solvent phases, typically n-octanol and water. An experimental log P is valid for only a single chemical species, while a mixture of chemical species is defined by a distribution, log D. Because log P is a ratio of two concentrations at saturation, it is essentially the net result of all intermolecular forces between a solute and the two phases into which it partitions (1) and is generally pH-dependent. According to Testa et al. (1) lipophilicity can be represented (Fig. 1) as the difference between the hydrophobicity, which accounts for hydrophobic interactions, and dispersion forces and polarity, which account for hydrogen bonds, orientation, and induction forces ... 

Induction forces. These arise when a molecule with a permanent dipole caused by a polar group (C-Cl, C=0, C-NO2), induces a dipole in a neighboring molecule. This effect is particularly strong with aromatics because of the high polarizability of the easily displaced -electrons-e.g., low molecular weight esters and polystyrene, or benzene and poly (vinyl acetate). 

Debye Induction Forces. These forces result from interaction between permanent and induced dipoles. 

Keesom Orientation Forces. These forces result from the interaction of two permanent dipoles, with the hydrogen bond being the most important. Hydrogen bonds are stronger than dispersion or inductive forces. 

Van der Waals postulated that neutral molecules exert forces of attraction on each other which are caused by electrical interactions between dipoles. The attraction results from the orientation of dipoles due to any of (1) Keesom forces between permanent dipoles, (2) Debye induction forces between dipoles and induced dipoles, or (3) London-van der Waals dispersion forces between fluctuating dipoles and induced dipoles. (The term dispersion forces arose because they are largely determined by outer electrons, which are also responsible for the dispersion of light [272].) Except for quite polar materials the London-van der Waals dispersion forces are the more significant of the three. For molecules the force varies inversely with the sixth power of the intermolecular distance. 

As seen for several of the examples, the fractional contribution of induction forces can be substantial for unlike molecular pairs. Roughly /(ind) is larger, the greater the difference in polarity of the interacting species. 

When one molecule is polar and the other nonpolar, the polar molecule induces a dipole in the nonpolar one. The two dipoles are again attracted by electrostatic forces, in this case designated as induction forces. These forces are considerably weaker than orientation forces but stronger than the attractive forces between nonpolar molecules. 

Ideal solution, 49 Inclusion compounds, 46, 266 Induction forces, 43, 44 Inorganic GC, 150 Internal standard, 105-106 Internal surface reverse phase LC column, 225... 

The other molecules in Table 2 have permanent dipoles and exhibit all three forces. Note that in the series of hydrogen halides, the dipole moment decreases as the size and polarizability increase hence orientation and induction forces decrease as dispersion forces increase in the series. 

Induction forces in the double layer caused by the electric field electrophoretic retardation)... 

These very weak forces arise by virtue of the polarization of a molecule by the charge or permanent electric moment on an adjacent molecule. In addition, polar bonds may result in bonds between atoms of greatly different electronegativity in which the shared pair of electrons are distorted from a symmetrical distribution. These induction forces, though of low energy, are of some import in the binding of lipids and proteins. 

Debye inductive force induced dipole-permanent dipole interaction [43,44]. 

For a pair of identical molecules, it is noted in Eq. (13) that the first term determined with regard to the deformation polarizability is a so-called Debye inductive force , and the second term is generally called a Keesom orientational force between molecules when the dipole moment is considered in the intermolecular attractive system. 

Induction forces brought about by the operation of a surface electric field on induced or permanent dipoles of resident molecules... 

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