RELATIONSHIP BETWEEN INTRAMOLECULAR CHEMICAL-EXCHANGE AND NMR-OBSERVED RATE CONSTANTS

This paper shows that the rate constants measured by dynamic NMR methods differ from those of the chemical process(es) giving rise to the exchange and that the chemical rate constants one can derive depend on the mechanism under consideration. Thus, the indiscriminate use of measured rate constants can in unfavorable cases lead to serious errors and consequent incorrect mechanistic interpretation. A simplified method for obtaining rate constants from dynamic NMR experiments in which the exchange processes are defined by more than a single rate-limiting step is described. In addition, the method can be used in the construction of kinetic (Kubo-Sack) matrices.