Chemical Exchange

Abstract

In magnetic resonance, the term chemical exchange has a specific meaning. It means that a chemical system is at macroscopic equilibrium, but at the microscopic level, an individual nucleus is exchanging its environment with another nucleus. The process causes no net change in the sample, but from the point of view of a particular nucleus, a chemical reaction has occurred. Another common term is Dynamic NMR (DNMR), which emphasizes the fact that molecules always have some motion associated with them. Apart from being an interesting aspect of spectroscopy, chemical exchange is important and useful for the same reasons as other types of chemical kinetics. Transition-state theory tells us that the rate is related to the thermodynamics of the barrier. Kinetics is one of the few ways we have of studying the transition state.