Electrostatic potential similarity

Figure 2.2. Pairwise percentage sequence identity for 33 cupredoxins plotted against (A) hydrophobic MIF similarity index and (B) electrostatic potential similarity index. The linear regression correlation coefficients...

The electrostatic potential within a phase, that is, l/e times the electrical work of bringing unit charge from vacuum at infinity into the phase, is called the Galvani, or inner, potential Similarly, the electrostatic potential difference... 

The calculation of autocorrelation vectors of surface properties [25] is similar (Eq. (21), with the distance d XiXj) between two points and Xj on the molecular surface within the interval between d[ and d a certain property p, e.g., the electrostatic potential (ESP) at a point on the molecular surface and the number of distance intervals 1). 

Hodgkin E E and W G Richards 1987. Molecular Similarity Based on Electrostatic Potential and Electri Field. International Journal of Quantum Chemistry. Quantum Biology Symposia 14 105-110. 

FIGURE 13.5 Isosurface plots, (a) Region of negative electrostatic potential around the water molecule. (A) Region where the Laplacian of the electron density is negative. Both of these plots have been proposed as descriptors of the lone-pair electrons. This example is typical in that the shapes of these regions are similar, but the Laplacian region tends to be closer to the nucleus. 

The greater positive character hence the increased acidity of the O—H proton of 2 2 2 tnfluoroethanol can be seen m the electrostatic potential maps displayed m Figure 1 8 Structural effects such as this that are transmitted through bonds are called indue tive effects A substituent induces a polarization m the bonds between it and some remote site A similar inductive effect is evident when comparing acetic acid and its trifluoro derivative Trifluoroacetic acid is more than 4 units stronger than acetic acid... 

Electrostatic Interaction. Similarly charged particles repel one another. The charges on a particle surface may be due to hydrolysis of surface groups or adsorption of ions from solution. The surface charge density can be converted to an effective surface potential, /, when the potential is <30 mV, using the foUowing equation, where -Np represents the Faraday constant and Ai the gas law constant. 

As useful as molecular models are, they are limited in that they only show the location of the atoms and the space they occupy. Another important dimension to molecular structure is its electron distribution. We introduced electrostatic potential maps in Section 1.5 as a way of illustrating charge distribution and will continue to use them throughout the text. Figure 1.6(d) shows the electrostatic potential map of methane. Its overall shape is similar to the volume occupied by the space-filling model. The most electron-rich regions are closer to carbon and the most electron-poor ones are closer to the hydrogens. 

Examine electrostatic potential maps for potassium hydride and hydrogen chloride. How are they similar and how are they different (Focus on whether the molecules are polar or nonpolar (compare dipole moments), and on the electronic character of hydrogen.) Draw the ionic Lewis structure that is most consistent with each electrostatic potential map. Does each atom have a filled valence shell ... 

Compare geometries, atomic charges and electrostatic potential maps of thionyl chloride and phosphorus trichloride. How are they similar How are they different Can you redraw the Lewis structure of SOCI2 so that it gives abetter description of the electrostatic potential map ... 

Examine the geometry and electrostatic potential map for acetone enolate. Are the CC and CO bonds in the enolate more similar to those in acetone or propen-2-ol precursors Is the negative charge primarily located on oxygen or on carbon Assuming this enolate is a hybrid of the two resonance contributors as shown above, which, if either, appears to be the major contributor ... 

Describe the similarities and differences in geometries, charge distributions and electrostatic potential maps for cyclopentadienyl sodium, cyclopentadiene and cyclopentadienyl anion. 

Compare electrostatic potential maps for the more stable form of CH2N2 and singlet methylene. Describe similarities and differences between the two. 

The dichlorocarbene carbon atom is syj- -hybridized, with a vacant p orbital extending above and below the plane of the three atoms and with an unshared pair of elections occupying the third sp2 lobe. Note that this electronic description of dichlorocarbene is similar to that for a carbocation Section 6.9) with respect to both the sp2 hybridization of carbon and the vacant p orbital. Electrostatic potential maps further show this similarity (Figure 7.6). 

As the following resonance structures indicate, enamines are electronically similar to enolate ions. Overlap of the nitrogen lone-pair orbital with the double-bond p orbitals leads to an increase in electron density on the a carbon atom, making that carbon nucleophilic. An electrostatic potential map of N,N-6imethyl-aminoethvlene shows this shift of electron density (red) toward the a position. 

For the electrostatic potential and the surface form, similar to the asymmetrical fluctuations, the following symmetrical fluctuations can be defined ... 

In the present work, we shall investigate the problem of the amount of correlation accounted for in the DF formalism by comparing the molecular electrostatic potentials (MEPs) and dipole moments of CO and N2O calculated by DF and ab initio methods. It is indeed well known that the calculated dipole moment rf these compounds is critically dependent on the level of theory implemented and, in particular, that introduction of correlation is essential for an accurate prediction [13,14]. As the MEP property reflects reliably the partial charges distribution on the atoms of the molecule, it is expected that the MEP will exhibit a similar dependence and that its gross features correlate with the changes in the value of dipole moment when switching from one level of theory to the other. Such a behavior has indeed been reported recently by Luque et al. [15], but their study is limited to the ab initio method and we found it worthwhile to extend it to the DF formalism. Finally, the proton affinity and the site of protonation of N2O, as calculated by both DF and ab initio methods, will be reported. 

Similar equations can be derived for the other ions. The charge density p x) is then obtained by adding the charge densities pertaining to all four kinds of ions. Both p x) and the electrostatic potential (f> x) are calculated by solving the Poisson equation self-consistently, and the particle distributions then follow by substituting (j)(x) into Eq. (25) and the respective equations for the other ions. 

Tasi, G., and Palinkd,1. Using Molecular Electrostatic Potential Maps for Similarity Studies. 174, 45-72 (1995). 

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