Ab initio calculations were carried out in order to obtain conformational, structural, and vibrational data for a set of small oxygen-containing phosphorus compounds. Many of these molecules are fundamentally important since they are analogous to macrostructures that play a central role in biological processes. It is anticipated that the chemical and physical properties of these phosphorus compounds will provide valuable insight into problems in structural biology. These calculations involved the use of the standard 6-31G** basis set at both the Hartree−Fock and Møller−Plesset levels of theory for the determination of rotational profiles, molecular geometries, and vibrational frequencies. Comparisons to experimental results are made when possible.

Molecular mechanics calculations play an important role in modern conformational analysis. Alkyl chlorides are useful organic compounds that have been used as important intermediates and target compounds of commercial and academic interest. Molecular modeling studies utilizing force field calculations have become very popular in the past decade, but in order to make quantitative predictions of unknown compounds it is critical to be able to calculate accurately the energy among conformational equilibrium structures and transition state barriers for known compounds of the same family. An MM3 force field for monochloroalkanes has been developed recently that accurately reproduces molecular structures and vibrational frequencies. This paper presents and compares MM3 calculations with experimental data (Raman, IR, ED, MW, and NMR) for selected cyclic and acyclic monochlorohydrocarbons.