Chemistry and Electrostatic Effects

MODELING CHEMISTRY AND ELECTROSTATIC EFFECTS 6.3.1. A Simple VB Formulation... 

Another of Conant s students was Frank Westheimer (b. 1912), who, after postdoctoral work with Hammett at Columbia, held a post at the University of Chicago (1936-1954) and then returned to Harvard. Westheimer worked in several areas of physical organic chemistry and engaged in other chemistry-based activities, as revealed in an interview conducted in 1995 by Istvan Hargittai.233 For much of his career, Westheimer was essentially a physical organic chemist working in biochemistry and he has himself written reflectively on the discovery of the mechanisms of enzyme action over the period 1947-1963234 and on the application of physical organic chemistry to biochemical problems.235 Westheimer has also contributed, as Tetrahedron Perspective Number 4, an article on Coincidences, decarboxylation, and electrostatic effects , which, he writes, ...allows me to review some of my past .236... 

Standing of surface charge and surface potential, and their relationship to pH, ionic strength, and medium composition. Westall and Hohl (1980) provide an excellent review of alternative models for the electrical double layer, and James and Parks (1982) provide a detailed description zind explanation of the surface chemistry and electrostatics of hydrous metal oxides. Hayes et al. (1988) present an excellent discussion of the effect of the electrical double layer on the adsorption of inorganic anions. A similar approach is used by Zachara et al. (1990) to model the adsorption of aminonaphthalene and quinoline onto amorphous silica. 

Manz, B Stilbs, P Jonsson, B Soderman, O Callaghan, PT, NMR Imaging of the Time Evolution of Electroosmotic Flow in a Capillary, Journal of Physical Chemistry 99, 11297, 1995. Matthew, JB Hanania, GIH Gurd, FRN, Electrostatic Effects in Hemoglobin Bohr Effect and Ionic Strength Dependence of Individual Groups, Biochemistry 18, 1928, 1979. 

The ionic theory thus has the advantage of isolating the quantum and other effects that are difficult to calculate into the potential C/iocai which is treated empirically (Section 3.1). The long-range effects which are important for crystal chemistry are then given by the Madelung term which can be readily calculated using classical electrostatic theory. 

Jprgensen57 has referred to this tendency of fluoride ions to favor further coordination by a fourth fluoride (the same is true for hydrides) as symbiosis." Although other factors can work to oppose the symbiotic tendency, it has widespread effect in inorganic chemistry and helps to explain the tendency for compounds to be symmetrically substituted rather than to have mixed substituents. We have seen (Chapter 5) that the electrostatic stabilization of C—F bonds (ionic resonance energy) will be maximized in CF4, and similar arguments can be made for maximizing hard-hard or soft-soft interactions. 

The forces involved in chemistry are essentially electrostatic. They are variants on the Coulomb force. We can distinguish two orders primary forces and secondary forces. Primary forces are those which hold the atoms together in molecules, and the oppositely charged ions in crystalline salts. Respectively, they are known as covalency and electrovalency (or, sometimes, the ionic force). The latter is directly electrostatic, the mutual attraction between Na+ and Cl" in common salt, for example. The former is usually figured as the sharing of an electron-pair between two atoms— Cl-Cl in the chlorine molecule, where the bond stands for a shared pair of electrons. We need quantum mechanics to understand why, in certain circumstances, electron density builds up in the region between the two chlorine atoms. Granted that it does so, we can explain the covalent bond as due to a resultant electrostatic effect. 

In molecules with heteroatoms there is always some charge separation. In these cases, and more importantly with compounds that include charged metal ions, electrostatic effects may be critical. The problem is that, apart from some recent and, at least in the area of coordination chemistry, not fully tested methods,8 there are no simple and accurate methods to calculate partial charges empirically. 

Holm C, Kekicheff P, Podgornik R (2001) Electrostatic Effects in Soft Matter and Biophysics. NATO Science Series II- Mathematics, vol 46. Physics and Chemistry, Kluwer Academic Publishers, Dordrecht... 

The essential realization in this spontaneous ordering process is the importance of noncovalent bonding interaction between molecules, that is, supramolecular chemistry. These conformation-specific interactions are governed by weak forces including hydrogen bonding, metal coordination, van der Waals forces, pi-pi interactions, and electrostatic Coulombic effects. The cooperative action of multiple noncovalent interaction forces is precisely the path nature takes to produce shape and form. 

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