Molecular electrostatic potential contours

Fig. 1. Molecular electrostatic potential contour plot (values in au) for a portion of the benzene molecule in the molecular plane. Carbon nuclei are located at C and D with the hydrogen nuclei at C and >. Saddlepoint-like structures are seen at the points P and F. (Reproduced from [9] copyright-American Institute of Physics)...

The above G(a) surface is a molecular electrostatic potential contour surface, MEPCO, for the contour value a. Note that in contrast to the case of electronic charge density contours, in a MEP analysis the function V(r), hence the threshold parameter a, can take both positive and negative values. 

Fig. 3-2. Molecular electrostatic potential with 6-31G //3-21G basis set in the molecular plane of (ii)-nitrous acid. Black dots refer to four different protonation sites in potential minima. For values of isopotential contours see Nguyen and Hegarty, 1984.

Fig. 5. A contour plot representing a two-dimensional slice of the molecular electrostatic potential for vinyl sulfone in the plane of the molecule with a sample uniform cubic grid superimposed grid points would be placed at the intersections of the perpendicular lines. (Reproduced from [71] copyright-John Wiley Sons)...

J.J. Kaufman, P.C. Hariharan, F.L. Tobin, and C. Petrongolo, "Electrostatic Molecular Potential Contour Maps from Ab Initio Calculation", in Chemical Applications of Atomic and Molecular Electrostatic Potentials, P. Politzer and D.G. Truhlar (Eds.), Plenum, New York, 1981, pp. 335-380. 

Figure 1 Contour map of the negative of the molecular electrostatic potential for acetamide at the HF/3-21G( ) level calculated from the full molecular wavefunction. Shading indicates approximate value of the potential in the region. Thus, the MEP near the oxygen is negative, and the MEP near the amide hydrogens (not shown) is positive. The basis set has polarization functions only on second-row atoms.

Figure 2 Contour map of the negative of the molecular electrostatic potential for acetamide at the HF/S-ZIGI ) level calculated using the monopole approximation and the CHELP charges. Scale same as in Figure 1.

A general method, proposed by Politzer and coworkers, to estimate physico-chemical properties depending on noncovalent interactions [Brinck et ai, 1993 Murray et al., 1993 Politzer etal., 1993 Murray et al., 1994]. This is based on molecular surface area in conjunction with some statistically-based quantities related to the - molecular electrostatic potential (MEP) at the - molecular surface. The electron isodensity contour surface [0.001 a.u. contour of Q(r)j is taken as the molecular surface model. 

Figure 4 Molecular electrostatic potential of water molecule, represented as a contour plot with intervals of 0.025 au. Red contours indicate regions of negative potential and blue represents positive, (a-b) Potential generated from full electron density, in and perpendicular to the molecular plane, respectively (c d) potential generated from point charges situated at three atomic positions (e-f) potential generated from point charges and dipoles situated at three atomic positions. (See color plate at end of chapter.)...

Figure L Molecular topology, atomic numbering, and in-plane molecular electrostatic potential energy maps for a, 9-methylguanine (9-MeG) b, 9-methyladenine (9-MeA) c, 1-methylcytosine (1-MeC) and d, the N 1-deprotonated thymine monoanion (Thy ). Contour levels for the electrostatic potential energy maps are given in kcal/mol as in Ref. 21 and 26.

Figure 4.7. Shape of the molecular electrostatic potential in the outer space of digitoxigenin when occupying the probable receptor-bound conformation. Using the co-ordinates derived from X-ray crystal structure analysis, the equipotential energy contours (expressed in kJtmol) are calculated with the use of an optimized monopol expansion. The energy contours refer to the plane laid across carbon atoms 6, 8, and 9 involved in forming rings B and C. Reproduced from [128],...

Thus, one can see that the original definition of local hardness, with ( ) = pC I/N nicely embodies electrostatic effects. Far away from the nuclei the local hardness becomes proportional to the electrostatic potential generated by the molecular charge distribution. Since contour diagrams of molecular electrostatic potentials have been widely used to analyze the chemical reactivity of a great number of chemical species [31], it is to be expected that the local hardness index provided by Eq. (15) will incorporate additional effects, and this way it may become a very useful reactivity index. 

Fig. 2. Equipotential contour map of the molecular electrostatic potential (MEP) of H2O at intervals of 15.94 X 10 fc(SCF/4 — 31G ). Full lines, MEP < 0 dotted lines, MEP > 0 dashed line, MEP = 0. Left section in the molecular plane a ) right perpendicular section in the symmetry plane ((t )...

FIGURE 4.1 The potential contour maps for the molecules under discussion on their HOMO state. A higher density of contours indicates that the site is susceptible for electrophilic attack either for positive (green) or negative (in cyan) molecular electrostatic potential (Putz et al., 2010). 

PES representation, students are asked to predict the reaction path. Locations, geometries, and energies of the two minima and of the transition state are also extracted from the PES graph (Figure 4). The AMI and PM3 results are compared with experimental and ab initio data. The last assignment is devoted to the molecular electrostatic potential (MEP) and HOMO of five organic molecules, which are calculated using AMI and displayed as 2D contours plots in HYPERCHEM. For each molecule, the more favorable sites for electrophilic attack are deduced from the position of the MEP minima and from the HOMO localization. Differences are discussed and results are con elated with gas phase proton affinity. 

Wave functions can be visualized as the total electron density, orbital densities, electrostatic potential, atomic densities, or the Laplacian of the electron density. The program computes the data from the basis functions and molecular orbital coefficients. Thus, it does not need a large amount of disk space to store data, but the computation can be time-consuming. Molden can also compute electrostatic charges from the wave function. Several visualization modes are available, including contour plots, three-dimensional isosurfaces, and data slices. 

Find the molecular model of 18 crown 6 (see Figure 16 2) on Learning By Modeling and examine its electrostatic potential map View the map in vanous modes (dots contours and as a transparent surface) Does 18 crown 6 have a dipole moment Are vicinal oxygens anti or gauche to one another"d... 

The results of electrostatic potential calculations can be used to predict initial attack positions of protons (or other ions) during a reaction. You can use the Contour Plot dialog box to request a plot of the contour map of the electrostatic potential of a molecular system after you done a semi-empirical or ab initio calculation. By definition, the electrostatic potential is calculated using the following expression ... 

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