Modeling electric effects

Thus, we have considered in detail various theoretical models of effect of adsorption of molecular, atom and radical particles on electric conductivity of semiconductor adsorbents of various crystalline types. Special attention has been paid to sintered and partially reduced oxide adsorbents characterized by the bridge type of intercrystalline contacts with the dominant content of bridges of open type because of wide domain of application of this very type of adsorbents as sensitive elements used in our physical and chemical studies. 

Despite the strong interest in the correlation between torsion angle and transport properties, suitable model compounds enabling the systematic variation of the torsion angle in biphenyl systems have not been realized so far, and the role of geometric and electric effects of the substituents is still being actively discussed [48, 72, 74, 271, 277]. 

Taft and his coworkers14-16 developed a diparametric model which separated the electrical effect into contributions from the inductive (actually the field) and resonance effects. This separation depends on the difference in the extent of electron delocalization when a substituent is bonded to an sp3 -hybridized carbon atom in one reference system and to an sp2-hybridized carbon atom in another. As the first case represents minimal delocalization and the second extensive delocalization, we have referred to the two effects as the localized and delocalized electrical effects. This diparametric electrical effect model can be written in the form ... 

The final regression equation obtained will give a reasonable model of the electrical effect on the chemical reactivity in the data set of interest. 

Clearly there was a need for a more general model of electrical effects. Like the case of the Hammett equation the use of the LD equation for the description of chemical reactivities required either an a priori knowledge of the type of substituent constant required or a comparison of the results obtained using each of the available electronically deficient active sites. 

A triparametric model of the electrical effect has been introduced17 that can account for the complete range of electrical effects on chemical reactivities of closed shell species (carbenium and carbanions), that is, reactions which do not involve radical intermediates. The basis of this model was the observation that the electronic demand. On the assumption that they are generally separated by an order of magnitude in this variable it is possible to assign to each oq type a corresponding value of the electronic... 

In addition to these external electric or magnetic field as a perturbation parameter, solvents can be another option. Solvents having different dielectric constants would mimic different field strengths. In the recent past, several solvent models have been used to understand the reactivity of chemical species [55,56]. The well-acclaimed review article on solvent effects can be exploited in this regard [57]. Different solvent models such as conductor-like screening model (COSMO), polarizable continuum model (PCM), effective fragment potential (EFP) model with mostly water as a solvent have been used in the above studies. 

A given transport parameter has a fixed composition of Imf The existence of electrical effect teras In Equation 39 does not necessarily mean that they are due to Step 3 of the bloactlvlty model 13ie electrical effects observed may also be due to Imf Involved In Steps 1 and 2 ... 

The choice of electrical effect parameterization depends on the number of data points in the data set to be modeled. When using linear regression analysis the number of degrees of freedom, Ndf, is equal to the number of data points, Ndp, minus the number of independent variables, Ai,v, minus one. When modeling physicochemical data Ndf/Nj, should be at least 2 and preferably 3 or more. As the experimental error in the data increases, tVof/iViv should also increase. 

CR equation A diparametric electrical effect model using the composite act and pure parameters. A value of Pd is assumed and a value of q calculated. 

A major method of modeling the effect of structural variation on chemical reactivity, physical properties or biological activity of a set of substrates is the use of correlation analysis. In this method it is assumed that the effect of structural variation of a substituent X upon some chemical, physical or biological property of interest is a linear function of parameters which constitute a measure of electrical, steric, and transport effects. 

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