Westheimer force field calculations

The molecular mechanics technique has been called by many different names, including Westheimer method, strain-energy method, conformational energy calculations, empirical potential energy calculations, atom-atom pair potential method, and force field calculations. Empirical force field is widely used, but somewhat long, and many authors omit empirical, leading to confusion with spectroscopic force field calculations. Molecular mechanics (11) now appears to be favored (10a) and is used (abbreviated as MM) throu out this chapter. 

A system of analyzing the energy differences among molecules and among various geometries of a particular molecule has been developed, based on some fundamental notations formalized by Westheimer. The method is now known by the term molecular mechanics, although the expressions empirical force field calculations or the Westheimer method are sometimes applied. 

History and Concepts. A complementary approach for molecular structure calculations is available, and it is referred to as the molecular methanics or force field method it is also known as the Westheimer method. In 1946, twenty years after the impressive development of quantum theory, three papers appeared in the literature which applied classifical mechanical concepts to problems of chemical interest. Westheimer investigated the racemization of some optically active biphenyl derivatives. His work demonstrated the potential usefulness of molecular mechanics. The other two papers were attempts to tackle more complex problems. 

Still another method designed for the same purpose, namely equilibrium ground state geometries, must be mentioned. Starting with Westheimer s early calculations [141], the molecular mechanics or force field methods became a very important tool, especially for very large molecular systems, as encountered in biochemical applications. Here the contributions by Lifson/Warshel [142] and Allinger [143] deserve attention. 

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