Theoretical aspects of the coordination of molecules to transition metal centers

When bound in transition metal complexes, organic molecules such as olefins, acetylenes, polyenes, cyclopolyenes and carbenes exhibit a variety of equilibrium geometries. The range of observed barriers to a conformational change a s simple a s rotation areund the metal-ligand coordination axis is impres sively large, from 0 to > 40 kcal/mole. Clearly it is electronic factors that are operative in setting the preferred geometries in these molecules and in Controlling the magnitude of the conformational barriers. In this lecture several specific examples of the theory of these conformational phenomena will be presented. I