^(15)N Nuclear Magnetic Resonance Spectroscopy. Changes in Nuclear Overhauser Effects and T_1 with Viscosity
Abstract
A procedure is described for probing changes in ^(15)N T_1 relaxation rates and nuclear Overhauser effects (NOE) with viscosity as a function of temperature. The large freezing-point depression and high viscosities of 8.8 M dimethyl sulfoxide (DMSO)−water solutions allowed study of the molecular motions of several ammonium salts, amides, and heterocycles on the pico- to nanosecond time scale. Dipole−dipole interactions provide the dominant form of relaxation for the ammonium salts, but chemical-shift anisotropy (CSA) also plays a significant role in the relaxation of amides and heterocycles. For pyridine, CSA is a particularly important mechanism and the shielding anisotropy of pyridine in 8.8 M DMSO−water is estimated to be on the order of 325 ppm. The ^(15)N NOE of NH_4Cl is greater than the theoretical maximum for intramolecular dipolar relaxation at high viscosities, and can be accounted for either by significant intermolecular contributions operating on a different time scale or by rapid motional averaging.
Additional Information
© 1997 American Chemical Society. Received September 16, 1996. Revised Manuscript Received January 23, 1997. Publication Date (Web): March 26, 1997. We gratefully acknowledge the Summer Undergraduate Research Fellowship Program (SURF) and the Beckman Institute of the California Institute of Technology, the E. I. Du Pont Company, and Dr. & Mrs. Chester M. McCloskey for financial support of this research. We are deeply indebted to Professors David M. Grant and Bernard Gerstein for many helpful suggestions on the interpretation of our results. This paper is dedicated to Professors Yoshito Kishi and Dieter Seebach on the occasion of their 60th birthdays.Additional details
- Eprint ID
- 60711
- Resolver ID
- CaltechAUTHORS:20151002-123935438
- Caltech Summer Undergraduate Research Fellowship (SURF)
- Caltech Beckman Institute
- E. I. Du Pont Company
- Dr. and Mrs. Chester M. McCloskey
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2015-10-05Created from EPrint's datestamp field
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2021-11-10Created from EPrint's last_modified field