Electrostatic response potential

Figure 4.3.1. The electrostatic response potential < > induced by the solvent at the position of the solute ion, as a function of the solute charge. Dashed line - the Stockmayer-CHsCl model described in Secti

In the solvation theory a reformulation of electrostatic Equations (1.119) is expedient. The solute charge density p(r) serves as an input variable, i.e. the driving force. The target of a computation is the scalar solvent response potential [Pg.97]

All the models described above for the electrostatic response provide either the charge or dipole distribution due to a potential or field. To complete the description of an electrostatic model these equations must be combined with the appropriate equations that provide the dependence of the potential and field on the charge and dipole distribution. 

In this outline we have summarized only the sensitivities representing responses to a populational perturbation of the system. In real chemical processes both populational and electrostatic (external potential) perturbations take place, so that the full CSA should also involve a supplementary investigation of the external potential related quantities. For this part of the CSA development the reader is referred to Refs. [39, 41, 47]. 

C(t) is the time eorrelation funetion of equilibrium fluctuations of the solvent response potential at the position of the solute ion. The electrostatic potential in C(t) will be replaced by the electric field or by higher gradients of the electrostatic potential when solvation of higher moments of the eharge distribution is considered. 

The electrostatic potential map of benzene (Figure 11 3c) shows regions of high electron density above and below the plane of the ring which is where we expect the most loosely held electrons (the rr electrons) to be In Chapter 12 we will see how this region of high electron density is responsible for the characteristic chemical reactivity of benzene and its relatives... 

FIGURE 19 2 Attrac tions between regions of positive (blue) and negative (red) electrostatic potential are responsible for intermo lecular hydrogen bonding between two molecules of acetic acid... 

Response to Electric and Acoustic Fields. If the stabilization of a suspension is primarily due to electrostatic repulsion, measurement of the zeta potential, can detect whether there is adequate electrostatic repulsion to overcome polarizabiUty attraction. A common guideline is that the dispersion should be stable if > 30 mV. In electrophoresis the appHed electric field is held constant and particle velocity is monitored using a microscope and video camera. In the electrosonic ampHtude technique the electric field is pulsed, and the sudden motion of the charged particles relative to their counterion atmospheres generates an acoustic pulse which can be related to the charge on the particles and the concentration of ions in solution (18). 

Decide if ion-dipole interactions are responsible for the observed substituent effects. Obtain the charge on carbon and nitrogen in each cyano group. What evidence is there for a polar CN bond Should the ion (O )-dipole (CN) interaction be stabilizing or destabilizing Can these interactions explain the trends in electrostatic potential (Hint Focus on changes in O—CN distance and in orientation of the cyano group.)... 

What other factors might be responsible for difference in activation energies Compare atomic charges anc electrostatic potential maps for the Sn2 transition states Does the increase in steric crowding lead to enhanced o diminished charge delocalization Explain. How, if at all would this be expected to affect the energy barrier Why ... 

Examine the structure of penicillin model (R=H), a model for the active compounds. What, if anything, distinguishes it from a typical amide (N,N-dimethylacetamide, for example) What is responsible for the differences Compare electrostatic potential maps for penicilhn model and dimethylacetamide. Which compound is more likely to undergo nucleophilic attack Explain. 

We can distinguish between static theories, which in essence give a description of the electron density, and dynamic theories, where an attempt is marie to measure the response of a molecule to (e.g.) an approaching N02" " ion. In recent years, the electrostatic potential has been used to give a simple representation of the more important features of molecular reactivity. It can be calculated quite easily at points in space ... 

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