Rotational Relaxation and Chemical Exchange

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Abstract
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.