Molecular conformation, prediction through models

One of the most important advances in molecular quantum mechanics of the last fifteen years has been the increased ease and accuracy of predicting molecular conformation through purely theoretical models [1-4]. The stable geometries of molecules as yet unmade can be determined and molecular properties of these systems studied. The conformations and properties of electronically excited molecules can be examined theoretically, whereas experimentally these geometries are often very elusive. Transition states, the species that separates reactants from products, and that have but fleeting existence — if at all, experimentally — are also obtainable using molecular quantum quantum mechanics. 

Another aspect of these computations was to obtain the most favorable configuration of the adsorbed molecule on a given inorganic surface. The theoretical results were validated with experimental data. For example, as observed in experimental investigations, two most stable fluorite-oleate complexes, namely, unidentate and bidentate, were predicted through molecular modeling calculations as well [36]. As shown in Figure 18.2, the theoretically simulated conformation (as indicated... 

The conformational entropies of copolymer chains are calculated through utilization of semiempirical potential energy functions and adoption of the RIS model of polymers. It is assumed that the glass transition temperature, Tg, is inversely related to the intramolecular, equilibrium flexibility of a copolymer chain as manifested by its conformational entropy. This approach is applied to the vinyl copolymers of vinyl chloride and vinylidene chloride with methyl acrylate, where the stereoregularity of each copolymer is explicitly considered, and correctly predicts the observed deviations from the Fox relation when they occur. It therefore appears that the sequence distribution - Tg effects observed in many copolymers may have an intramolecular origin in the form of specific molecular interactions between adjacent monomer units, which can be characterized by estimating the resultant conformational entropy. 

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