Westheimer concepts

Whereas many scientists shared Mulliken s initial skepticism regarding the practical role of theory in solving problems in chemistry and physics, the work of London (6) on dispersion forces in 1930 and Hbckel s 7t-electron theory in 1931 (7) continued to attract the interest of many, including a young scientist named Frank Westheimer who, drawing on the physics of internal motions as detailed by Pitzer (8), first applied the basic concepts of what is now called molecular mechanics to compute the rates of the racemization of ortho-dibromobiphenyls. The 1946 publication (9) of these results would lay the foundation for Westheimer s own systematic conformational analysis studies (10) as well as for many others, eg, Hendrickson s (11) and Allinger s (12). These scientists would utilize basic Newtonian mechanics coupled with concepts from spectroscopy (13,14) to develop nonquantum mechanical models of structures, energies, and reactivity. 

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. 

Theoretical approaches to the study of protein structure and function draw upon concepts and techniques from theoretical chemistry, including molecular mechanics, reaction dynamics, quantum and statistical mechanics (Brooks et al. 1988). Molecular mechanics methods were first developed for the study of small organic molecules (Barton 1948 Westheimer 1956 Hendrickson 1961 Wiberg 1965 Allinger et al. 1967 ... 

The Generation of Metaphosphoric Acid Derivatives. These are among the most reactive of low-coordinate phosphorus species, and are of great importance as reactive intermediates in some phosphorylation processes. The metaphosphate ion receives study as a possible intermediate in biological processes, a concept introduced in 1955 by the laboratories of F. H. Westheimer (6) and of C. A. Bunton (7). The... 

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

We now turn to the theoretical interpretation of these variable isotope effects, and in particular the occurrence of a maximum effect when AG° is close to zero. Since this last statement implies some kind of symmetry in the system, all theoretical treatments of the problem have involved the degree of symmetry or the extent of proton transfer in the transition state, concepts which have already been mentioned (p.216). The most commonly accepted explanation was first put forward by Westheimer and has been elaborated by a number of authors. Most of these "" adopt a linear three-centre model for the transition state and consider only... 

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