Rotational correlation time ( τ c {\displaystyle \tau _{c}} ) is the average time it takes for a molecule to rotate one radian.
In solution, rotational correlation times are in the order of picoseconds. For example, the τ c = {\displaystyle \tau _{c}=} 1.7 ps for water, and 100 ps for a pyrroline nitroxyl radical in a DMSO-water mixture. Rotational correlation times are employed in the measurement of microviscosity (viscosity at the molecular level) and in protein characterization.
Rotational correlation times may be measured by rotational (microwave), dielectric, and nuclear magnetic resonance (NMR) spectroscopy. Rotational correlation times of probe molecules in media have been measured by fluorescence lifetime or for radicals, from the linewidths of electron spin resonances.
References
Krishnan, V.V.; Cosman, Monique (July 1998). "An empirical relationship between rotational correlation time and solvent accessible surface area". Journal of Biomolecular NMR. 12 (1): 177–182. doi:10.1023/A:1008226330666. PMID 20700691 – via Springer Nature Link. https://link.springer.com/article/10.1023/A:1008226330666 ↩
Lankhorst, D.; Schriever, J.; Leyte, J. C. (March 1982). "Determination of the Rotational Correlation Time of Water by Proton NMR Relaxation in H217O and Some Related Results". Berichte der Bunsengesellschaft für physikalische Chemie. 86 (3): 215–221. doi:10.1002/bbpc.19820860308. /wiki/Doi_(identifier) ↩
Bulla, Ivan; Törmälä, Pertti; Lindberg, J. Johan; Mikalsen, Øyvind; Southern, J. T.; Edlund, Kaj; Eliasen, Mogens; Herskind, Carsten; Laursen, Thomas (1975). "Spin Probe Studies on the Dynamic Structure of Dimethyl Sulfoxide-Water Mixtures". Acta Chemica Scandinavica. 29a: 89–92. doi:10.3891/acta.chem.scand.29a-0089. https://doi.org/10.3891%2Facta.chem.scand.29a-0089 ↩
Reich, Hans J. "8.1 Relaxation in NMR Spectroscopy". organicchemistrydata.org. Retrieved 2020-09-12. https://organicchemistrydata.org/hansreich/resources/nmr/#08-tech-01-relax/ ↩
Bulla, Ivan; Törmälä, Pertti; Lindberg, J. Johan; Mikalsen, Øyvind; Southern, J. T.; Edlund, Kaj; Eliasen, Mogens; Herskind, Carsten; Laursen, Thomas (1975). "Spin Probe Studies on the Dynamic Structure of Dimethyl Sulfoxide-Water Mixtures". Acta Chemica Scandinavica. 29a: 89–92. doi:10.3891/acta.chem.scand.29a-0089. https://doi.org/10.3891%2Facta.chem.scand.29a-0089 ↩