Dipole induction interaction

Dipole induction interaction occurs when a permanent dipole induces a temporary dipole in a neighbouring molecule that does not necessarily possess a dipole moment of its own. 

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]... 

Considerably larger stabilization energies of protonated pairs are due to the molecular ion-molecular dipole electrostatic and molecular-ion-induced dipole induction interactions. Both interactions, covered already in the HF interaction energy, are very strong in protonated pairs with a highly polar neutral monomer. For example, the calculated gas phase complexation energy of the triply bonded CCH+ pair is —45 kcal mol . ... 

The theory has been extended to polar solvents by including dispersion 5, permanent dipole orientation 5q, dipole induction 8ind> and hydrogen-bonding interactions 5ii such as acidic 5 and basic 8i,. In this case the solubihty parameter 5j is given by Equation 4.5 ... 

For polarizable charge distributions, additional classical-type interactions arise from the induced dipole, quadrupole, and higher moments on each monomer, which are proportional to the fields created by the asymmetric charge distribution on the other monomer. The proportionality constants for each multipole field are the monomer polarizabilities aa and ah (a111 for dipole fields, a(Q) for quadrupole fields, etc.). The leading two induction interactions are ... 

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. 

Intermolecular forces will determine the behavior of all materials in every phase in which they exist. Intermolecular forces can be classified into (1) dispersion, (2) dipole, (3) induction, and (4) hydrogen bonding. The relative strength of these forces can be stated as dispersion < dipole < induction < hydrogen bonding. Owing to the low polarizability of the C—F bond, the dominant intermolecular force is often dispersive in character. The extension to more dominant forces should become obvious as more complicated molecules are discussed. The discussion here can be confined to simple pair-wise interactions between two molecules or polymer chains that contain C—F bonds. 

Welsh suggested correctly that similar transitions take place even if the molecular pair is not bound. The energy of relative motion of the pair is a continuum. Its width is of the order of the thermal energy, Efree 3kT/2. Radiative transitions between free states occur (marked free-free in the figure) which are quite diffuse, reflecting the short lifetime of the supermolecule. In dense gases, such diffuse collision-induced transitions are often found at the various rotovibrational transition frequencies, or at sums or differences of these, even if these are dipole forbidden in the individual molecules. The dipole that interacts with the radiation field arises primarily by polarization of the collisional partner in the quadrupole field of one molecule the free-free and bound-bound transitions originate from the same basic induction mechanism. 

At this pressure, the polarizability/volume of SF CO2 is a little less than that of n-hexane, which suggests that there are other molecular interactions between CO2 and phenol blue in addition to dispersion and induction. The likely possibilities include electron donor-acceptor forces and dipole-quadrupole interactions. 

Dipole-dipole interactions have been used to assess the conformational populations of 2-haloketones (Eliel et al., 1965). With respect to SS, however, there are few applications in which these and related effects are considered. It is interesting that dipole induction and London dispersion effects were used some thirty years ago to account for the high endo over exo preference in the Diels-Alder reaction (Wassermann, 1965). Although effects are small for any pair of atoms, there are many closely packed atoms in a Diels-Alder transition state. At a carbon-carbon distance of 2-0 a between the atoms to be bonded, the energy favoring endo addition is 2-7 for dipole induction and 3-4 kcal/mole for dispersion in the reaction of cyclopentadiene with p-benzoquinone (Wassermann, 1965). These nonbonding attractive energies cooperate with the secondary HMO effects discussed earlier to lead to an endo product. 

Table 2.4 lists the individual contributions or partial polarities for the solutes that appear in table 2.2. From this table, it is clear that a distinction can now be made between molecules of similar overall polarity. Much of the cohesive energy of toluene is due to dispersion interaction, whereas dipole orientation is more important in ethyl acetate. Orientation interaction is of more relevance in methylene chloride than it is in dioxane, which shows a considerable contribution from induction interaction. 

Liquids containing permanent dipoles have additional attractive interactions called Keesnm forces, which are caused by the tendency of the permanent dipoles to align anti-parallel with each other. Finally, there are also Debye or induction interactions between permanent dipoles and fluctuating ones. The dispersion interactions are the most important of the three types, however, because they occur in all materials, and are usually stronger than the Keesom and Debye interactions, when the latter are present at all. 

There are other forces, principally electrical in nature, present in molecular arrays whose constituents possess a permanent dipole (H2O, NH3). The energy resulting from such dipole-dipole interaction is also called the orientation energy. A charged species can also induce a dipole (induction energy). 

Lastly, we turn to consideration of the Rg—HF heterodimers (the atom—diatomic molecule system of the right-hand side of Figure 5.2), where a crucial role is played by the induction interaction occurring between the higher multipole moments of HF and the induced dipoles originating the polarizability of the rare gas (Magnasco et al., 1989a). 

For van der Waals interactions between molecules in a gas phase, the orientation interaction can yield from 0% (nonpolar molecules) up to 70% (molecules of large permanent dipole moment, like H2O) of the value of the contribution of the induction interaction in oi j is usually low, about 5 to 10% the contribution of the dispersion interaction might be between 24% (water) and 100% (nonpolar hydrocarbons) for numerical data, see Reference 34. 

As we have seen, London dispersion interactions, Keesom dipole-dipole orientation interactions and Debye dipole-induced dipole interactions are collectively termed van der Waals interactions their attractive potentials vary with the inverse sixth power of the intermol-ecular distance which is a common property. To show the relative magnitudes of dispersion, polar and induction forces in polar molecules, similarly to Equation (78) for London Dispersion forces, we may say for Keesom dipole-orientation interactions for two dissimilar molecules using Equation (37) that... 

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