Dipole induction

As already mentioned molecules cohere because of the presence of one or more of four types of forces, namely dispersion, dipole, induction and hydrogen bonding forces. In the case of aliphatic hydrocarbons the dispersion forces predominate. Many polymers and solvents, however, are said to be polar because they contain dipoles and these can enhance the total intermolecular attraction. It is generally considered that for solubility in such cases both the solubility parameter and the degree of polarity should match. This latter quality is usually expressed in terms of partial polarity which expresses the fraction of total forces due to the dipole bonds. Some figures for partial polarities of solvents are given in Table 5.5 but there is a serious lack of quantitative data on polymer partial polarities. At the present time a comparison of polarities has to be made on a commonsense rather than a quantitative approach. 

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 ... 

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. 

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. 

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]... 

Fig. 2.2 Dipole induction by displacement of an electron orbit in an atom.

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). 

Electron polarization, which is due to the deformation of the electron hull of the atoms constituting the dielectric material. Owing to the small mass of the particles involved (electrons), the rate of dipole induction is very fast (highest frequency part). 

Quadrupole induction pair potential energy is less than dipole induction pair potential energy. 

Very recently, Good [17] has extended the theory of interfacial energies [16] to include an explicit accoxmt of the different types of inter molecular forces dispersion, dipole induction, and dipole orientation. In the present paper, we will use the theory, as extended [17], to show how the actual surface free energies of certain solids can be calculated from contact angle data, including Fox and Zisman s critical surface tensions. 

Such endo preference is usually explained by attractive interactions (between TT-electron systems or because of dipole induction forces) between the diene and the dienophile at non-bonding positions in the transition state (see Section 7) this seems to justify both its regularity and the small values of the relative stabilisation energy. Other interpretations point to the direction that steric repulsion in some exo transition states (for instance when the diene is cyclo-pentadiene, with its methylene hydrogen atoms) must give to the course of the addition . 

Every dipole has an electric field associated with it. This electric field is capable of inducing relative displacements of the electrons and nuclei in neighboring molecules. The result is that the surrounding molecules become polarized, i.e., possess induced dipoles. Intermolecular forces, called induction forces, exist between the permanent and induced dipole. Induction forces are weak and temperature independent. The ease with which molecules can be polarized — referred to as polarizability — varies. 

The three types of interaction vary in quantitative importance from substance to substance. With carbon monoxide, for example, the London forces account for almost all the interaction, while with water, which possesses a large permanent moment, the orientation forces are estimated to account for about four-fifths of the total effect. The dipole induction forces are, on the whole, much less important. 

Polar interactions accompanied by the dipole induction. These interactions are asymmetrical. 

Intermolecular intertictions are a superposition of the forces of dipole, inductive, and disperse interactions. Such a composition is often approximated with the Lennard-Johns (12,6) potential... 

The forces of intermolecular interactions are the superposition of the dipole, induction, and disperse interaction forces. They can be expressed as a united function of interactions, such as the sum of two power functions Equation 1.7-39 (the Lennard-Johns potential), the potential pit, etc. 

The pair interaction potential models the interatetion among the molecules in any substance and is a superposition of van der Waals (intcrmolecular) forces of repulsion and attraction of different nature, namely, dipole, inductive, and disperse ones. 

Three fundamental dipoles Inductive (L), Capacitive (C), Conductive (G)... 

Two mixed dipoles Inductive-Conductive (L-G), Capacitive-Conductive (C-G)... 

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