An NMR Investigation of the Effect of Hydrogen Bonding on the Rates of Rotation about the C−N Bonds in Urea and Thiourea
Abstract
The interaction between urea and tetrabutylammonium acetate was investigated in dimethylformamide/dimethyl sulfoxide solutions using ^1H and ^(15)N NMR. The chemical-shift behavior of the urea protons is consistent with a urea-acetate hydrogen-bonded complex involving both carboxylate oxygens and the urea hydrogens trans to the carbonyl oxygen with K_(assoc) = 120 ± 10. Line shape analysis of the temperature-dependent ^1H NMR spectra show that ΔG^⧧ for rotation about the C−N bond of urea changes only slightly from 11.0 ± 0.1 to 11.2 ± 0.1 kcal/mol on 1:1 molar addition of tetrabutylammonium acetate to a dilute solution of urea. A parallel investigation of the interaction of thiourea with tetrabutylammonium acetate gave a binding constant, K_(assoc) = 90 ± 10. The ΔG^⧧ for rotation about the C−N bond of thiourea was found to increase from 13.5 ± 0.1 to 14.0 ± 0.1 kcal/mol on 1:1 addition of tetrabutylammonium acetate to a dilute solution of thiourea in dimethylformamide/dimethyl sulfoxide. Measurements were also made of the self-association of several ureas and of ΔG⧧ for rotation about both C(O)−N bonds of 1,1-dimethylurea.
Additional Information
© 1996 American Chemical Society. Received April 26, 1996. This paper is dedicated on the occasion of his 80th birthday to Nelson J. Leonard, an inspiration and friend for more than 50 years. We are grateful to Peter Wei for assistance with the ^(15)N NMR experiments as well as Linda Hanely and Francoise Gregoire for help with other NMR spectra. We also thank Steve Arvedson, Curt Hastings, and Dr. Robert Lee for technical consultations and useful conversations. This research was supported in part by the Caltech Summer Undergraduate Research Fellowships (SURF) to whom we are most appreciative. Further support was provided by the Arthur C. Cope Fund of the American Chemical Society and by Dr. and Mrs. Chester M. McCloskey.Additional details
- Eprint ID
- 60712
- DOI
- 10.1021/JA961380K
- Resolver ID
- CaltechAUTHORS:20151002-123935735
- Caltech Summer Undergraduate Research Fellowship (SURF)
- American Cancer Society
- Dr. and Mrs. Chester M. McCloskey
- Created
-
2015-10-05Created from EPrint's datestamp field
- Updated
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2023-06-01Created from EPrint's last_modified field
- Other Numbering System Name
- Caltech Gates and Crellin Laboratories of Chemistry
- Other Numbering System Identifier
- 9151