Dielectric Relaxation and Chemical Exchange

The coupling between molecular rotation and chemical exchange has been treated in several recent articles. It has been demonstrated that relaxation experiments can distinguish systems exchanging more slowly than the rate of molecular rotation from systems experiencing faster exchange. In analysing such experiments, however, one must draw careful distinctions between active and inactive relaxation mechanisms. The present article deals with these distinctions. The variation of dielectric relaxation with composition is analysed in several limiting situations. It is shown that “slow” and “fast” exchange are distinguishable in general, but that the treatment of experimental data will vary in different cases.