Crystallographic approaches to transition state structures

This chapter reviews crystallographic approaches to transition state structure. It appears to be a contradiction in terms— crystal structures give us information specifically about ground states, averaged over a period of hours or even days, whereas transition states for bond making or breaking—as defined by transition state theory—do not exist for any significant length of time. The approach discussed in the chapter—like any experimental approach currently available—is indirect and based on extrapolation. When the extrapolation is based on strong, directly relevant correlations, it can be remarkably effective. The subject spans two disciplines, organic mechanism and crystallography, without much intellectual overlap. This chapter also considers recent attempts to extrapolate from observed structures to the experimentally unattainable transition state structures for bond making and breaking reactions. The approach builds on the regular correlations between structure and reactivity, particularly the linear correlations with bond length describes in this chapter. © 1994 Academic Press Limited