ROTATIONAL RELAXATION AND CHEMICAL EXCHANGE

This article couples chemical exchange to rotational relaxation in liquids. We found that the relative rates of exchange and molecular rotation have a profound effect on relaxation behavior. Systems exchanging more slowly than the rate of molecular rotation can be distinguished from systems experiencing faster exchange. This leads to a novel class of experiments using molecular rotation as a frequency standard for the exchange process. Since rotational correlation times are typically 10-10-10-12 sec. these experiments provide sensitivity on a time scale not easily achieved by other techniques. Analysis of these experiments is presented. Studies of NMR spin-lattice relaxation in iodine charge-transfer complexes substantiate this analysis.