Intermolecular interactions electrostatic type

The various properties of molecules that can be used in a QSAR are often designed to quantitate the tendency of the molecules to participate in one of the fundamental types of intermolecular interactions electrostatic, hydrogen bonding, dispersion forces, and hydrophobic interactions. In addition, the possibility of steric interference with an interaction is considered. Other methods capitalize on the fact that the 2D structure of a molecule indirectly encodes its properties, instead generate descriptors without an explicit relationship to some physical property. 

In a solution of a solute in a solvent there can exist noncovalent intermolecular interactions of solvent-solvent, solvent-solute, and solute—solute pairs. The noncovalent attractive forces are of three types, namely, electrostatic, induction, and dispersion forces. We speak of forces, but physical theories make use of intermolecular energies. Let V(r) be the potential energy of interaction of two particles and F(r) be the force of interaction, where r is the interparticle distance of separation. Then these quantities are related by... 

A virtue of the potential distribution theorem approach is that it enables precise assessment of the differing consequences of intermolecular interactions of differing types. Here we use that feature to inquire into the role of electrostatic interactions in biomolecular hydration. 

In Eqs. (16) and (17), a and P refer to atoms of the solute and solvent, respectively q is the permittivity of free space, Qa and Qp are atomic charges, and Rap is the distance between atoms a and p. The parameters eap, aap, Aap, Bap and Cap can either be assigned by fitting to experimental data or can be the arithmetic or geometric means of literature values for the individual atom types.10,65,66 The atomic charges are commonly determined by requiring that they reproduce the calculated molecular electrostatic potentials.10 In order to provide better descriptions of the solvent s structure, Eqs. (16) and (17) are generally extended to include solvent-solvent intermolecular interactions. 

Before ending this chapter, we would like to draw attention to another type of electrostatic intermolecular interaction that could be quite relevant to hydroxylamines, oximes and hydroxamic acids. We refer to a-hole bonding. This is a highly-directional, nonco-valent interaction between a region of positive electrostatic potential (or cr-hole) on an outer portion of a Group V, VI or VII covalently-bonded atom and a negative site on... 

The results of Table XIX indicate that, in fact, the intermolecular interaction energies are significantly greater in the dimer 86 than in the dimer 87. It may certainly be extrapolated that the same situation would prevail in higher polymers of the two types. It is also interesting to underline that the major part of the bonding energy comes from the electrostatic component. 

In the development of the set of intermolecular potentials for the nitramine crystals Sorescu, Rice, and Thompson [112-115] have considered as the starting point the general principles of atom-atom potentials, proven to be successful in modeling a large number of organic crystals [120,123]. Particularly, it was assumed that intermolecular interactions can be separated into dispersive-repulsive interactions of van der Waals and electrostatic interactions. An additional simplification has been made by assuming that the intermolecular interactions depend only on the interatomic distances and that the same type of van der Waals potential parameters can be used for the same type of atoms, independent of their valence state. The non-electric interactions between molecules have been represented by Buckingham exp-6 functions,... 

More recently, in addition to random ionomers, telechelic ionomers in which ionic groups are located only at the chain end(s) became available and were used for the study of polyelectrolyte behavior [26-29]. Discussion was made from the point of view that the behavior of telechelic ionomers in nonaqueous solutions is basically similar to that of polyelectrolytes in aqueous/nonaqueous solutions (including random ionomers in nonaqueous solutions). Also, the study of fundamental aspects of polyelectrolytes was made possible because of the simplicity of the structure of telechelic ionomers. For example, telechelic ionomers with only one ionic group at the chain end can be used to study the role of intermolecular interactions, since there is no intramolecular electrostatic interaction available for this type of ionomer [27]. Due to space limitations, this chapter will only cover polyelectrolyte behavior of random ionomers in polar solvents. Some results on telechelic ionomers can be found elsewhere [26-29]. 

These results confirm the observation that polyelectrolyte aqueous solutions show two separate decay modes in the autocorrelation function and support our contention that ionic polymer systems generally behave similarly in polar solvents [23], To support this, it may be added that similar dynamic scattering behavior was recently reported for another type of ionomer, polyurethane ionomer, dissolved in a polar solvent, dimethylacetamide (e = 38) [92], Finally, it should be stressed that the explanation given above for light scattering (both static and dynamic) behavior of salt-free polyelectrolytes is based on the major role of intermolecular electrostatic interactions in causing characteristic behavior. No intramolecular interactions are explicitly included to explain the behavior. This is in accord with our contention that much of the polyelectrolyte behavior, especially structure-related aspects, is determined by intermolecular interactions [23]. 

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