Polarization concept

Goez M 1995 An introduction to chemically induced dynamic nuclear polarization Concepts Magn. Reson. 7 69-86... 

In a previous article [8] a brief review of bifunctional chains of atoms with respect to their reactivities and modes of formation was presented. Consequently, the polarity concept is of some value to systematization of organic reactions and it should be helpful to planning synthesis. 

Additivity and interaction, intrinsically polar concepts, are basic in physical sciences... 

Cyclic /1-ketoesters have been treated with strong base (NaH/toluene CH3ONa/CH3OH) and afterwards with acetylenecarboxylates or ethyl propiolates. From the reaction mixture the corresponding cycloalkenes, enlarged by two carbon atoms, can be isolated in 50-70 % yield. In the transformations of / -ketoesters, given in Scheme IV/8, no intermediate could be detected. Therefore and because of the strong basic conditions used, the concept of a concerted reaction must be rejected in these cases, and a simple polar concept is preferred... 

The relationship between permeate flux and the flow characteristics in microfiltration processes is often described using the him model, which is based on the concentration polarization concept [38] ... 

Goez, M., An Introduction to Chemically Induced Dynamic Nuclear Polarization, Concepts Magn. Reson. 1995, 7, 69 86. 

Such a description now invokes the polarization concept. Let 2 be the energy of P2. and then polarization energy ( pol) is defined as... 

As noted above, Kossel introduced the idea that the transition from ionic to covalent substances is gradual, the covalence increasing with the mutual polarizing influence of ions. This idea was developed by Fajans and his school who defined the polarizabilities of ions and estimated the polarizing action of cations (Z/r ), but ultimately failed to create a quantitative theory. The reason is obvious [10] there are no completely ionic substances, only intermediate cases, more or less approaching this type. Hence the parameters of ideal ions are not available experimentally, the more so since ionic radii cannot be uniquely defined from interatomic distances (see Chap. 1). Thus the polarization concept remained only qualitative. However, the contribution in the bond energy of the polarizing effect of atoms can be described in the form that has proven itself for the van der Waals interaction (see Sect. 4.4), where the deviation of the A B distance from the mean of A A and B B distances is a function of the difference of the atomic polarizabilities... 

Very important is the application of the polarization concept to solids including the ionic compounds. Thus, using experimental values of e and V, the molar polarizations of 129 oxides and 25 fluorides of various metals were calculated according to Eq. 11.13 [85], from which the polarizations of 61 ions (Table S11.8) were determined by the additive method. Using tabulated values of ionic polarizations, one can calculate the molar polarizations of numerous ionic crystals, and by the deviation from the normal value one can conclude about the appearance of specific features such as piezo- or ferro-electrics, deformations of cations or changes of the bond character. 

Hg. S3. A universal plot of the same K-shell ionization data as in tig. 5.4 based upon the increased binding and polarization concept, me parameter is the ratb of the square of the velocity of the projectile to that of the drculating electron and is a screening parameter. See Basbas et al. [1.7] for a list of the sources of the data. 

Forming mental models of molecules will help you understand the polarity concept. 

In addition to the Debye model for dielectric bulk materials, other dielectric relaxations expressed according to Maxwell-Wagner or Schwartz "interfacial" mechanisms exist. For example, the Maxwell-Wagner "interfacial" polarization concept deals with processes at the interfaces between different components of an experimental system. Maxwell-Wagner polarization occurs... 

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