Quantum chemical investigation of the torsional potential in neutral organic phosphite and phosphate esters

Computer technology has progressed rapidly, and now its influence pervades all areas of modern life. This influence has been felt particularly strongly in technical and scientific disciplines; and is due largely to the development of supercomputers, vector and parallel algorithms, high-performance graphics workstations, and scientific visualization. These developments have led to the birth of a new area of scientific pursuit, computational science. In this environment computational chemistry has begun to flourish. Mathematical models of the behavior of molecules and chemical systems have been developed, and encoded on computers. Theoretical chemical models have reached a sufficient level of maturity to allow computational investigations of large molecular systems such as those of interest in biology. There are two models which are in common use in computational chemistry: molecular mechanics and molecular quantum mechanics. Molecular mechanics is a descriptive model with built-in dependence on empirical parameters and potential functions from classical physics. Molecular quantum mechanics is more fundamental in the sense that it is based on a set of hypotheses and no empirical parameters other than the fundamental constants of physics. The focus of this work is the application of quantum mechanical methods and state-of-the-art computational techniques to provide better understanding of the structure and conformational behavior of neutral organic phosphite and phosphate esters. The anomeric effect in 6-membered phosphite and phosphate ring systems is examined. A comparison of results from ab initio and semiempirical molecular orbital calculations (geometries, preferred conformations, energies, and dipole moments) with each other and with experiment is made.