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WIREs Comput Mol Sci
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Molecular electrostatic potentials and noncovalent interactions

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σ‐Holes and π‐holes are two types of regions of lower electronic density that are frequently found in molecules. There are often positive electrostatic potentials associated with them, through which the molecule can interact attractively with negative sites to form noncovalent bonds. The Hellmann–Feynman theorem shows that these interactions are Coulombic, where this must be understood to include polarization as well as electrostatics. Computed molecular electrostatic potentials have played major roles in elucidating the natures of σ‐hole and π‐hole bonding, but two key issues must be kept in mind: (1) the electrostatic potential at any point r reflects not only the electronic density at r but also contributions from all of the nuclei and electrons in the molecule; thus, the potential in a region does not necessarily correlate with the electronic density in that region. (2) When a molecule begins to interact with another molecule, ion, and so on, its electronic density and hence its electrostatic potential are immediately influenced to some extent by the electric field of the other entity. This induced polarization may significantly affect the molecule's interactive behavior. Both of these issues are discussed.

Panels (a) and (b) are the computed electrostatic potentials on the 0.001 au molecular surfaces of (a) NCCl and (b) NCH. In each case, the nitrogen is at the left. Gray circles show locations of nuclei. Color ranges, in kcal/mol: red, more positive than 20; yellow, between 20 and 0; green, between 0 and −20; blue, more negative than −20. Black and blue hemispheres indicate, respectively, the positions of the most positive and most negative potentials, the VS,max and VS,min. Panel (c) shows the density difference plot for the complex NCCl⋯NCH. NCCl is at the left. The spheres show the locations of the nuclei; blue = nitrogen, gray = carbon, green = chlorine, white = hydrogen. Regions of increased density are violet, with the outermost contour being 0.0005 au and the innermost 0.002 au. Regions of decreased density are greenish blue, with the outermost contour being −0.0005 au and the innermost −0.002 au. Panel (d) is the computed electrostatic potential on the 0.001 au surface of the complex NCCl⋯NCH. NCCl is at the left. Details are as in (a) and (b).
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Computed electrostatic potential on the 0.001 au molecular surface of the tetrazole 2. The chlorine is at the upper left, and the fluorine is at the right. Gray circles show positions of nuclei. Color ranges, in kcal/mol: red, more positive than 22; yellow, between 22 and 11; green, between 11 and 0; blue, negative. The black hemispheres indicate the locations of the most positive potentials, the VS,max.
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Computed electrostatic potential on the 0.001 au molecular surface of SO3, seen from above the plane of the molecule. Gray circles show positions of nuclei. Color ranges, in kcal/mol: red, more positive than 36; yellow, between 36 and 18; green, between 18 and 0; blue, negative. The black hemisphere is at the location of the most positive potential, the VS,max, directly above the sulfur.
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Two views of the computed electrostatic potential on the 0.001 au molecular surface of SeFBr. In panel (a), the selenium is in the foregraound, the bromine at the right. In panel (b), the fluorine is in the foregraound to the left, the bromine is in the foreground to the right. Color ranges, in kcal/mol: red, more positive than 28; yellow, between 28 and 14; green, between 14 and 0; blue, negative. Black hemispheres indicate the positions of the most positive potentials, the VS,max.
[ Normal View | Magnified View ]

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