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A proton NMR investigation of rotation about the C(O)-N bonds of urea

Zhao, Yiming and Raymond, Mary Katherine and Tsai, Helen and Roberts, John D. (1993) A proton NMR investigation of rotation about the C(O)-N bonds of urea. Journal of Physical Chemistry, 97 (12). pp. 2910-2913. ISSN 0022-3654 . http://resolver.caltech.edu/CaltechAUTHORS:20151002-123936293

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Abstract

The rates and activation energies have been determined by proton NMR for H_2^(15)N(CO)^(14)NH_2 1 and hydrogen exchange equilibrated mixtures of 1 and H_2^(15)N(CO)^(15)NH_2 2 with D_2NC(O)ND_2 3. Synthesis of 1 was achieved by the classic Wöhler procedure from ^(15)NH_4 C=^(14)N=O with no detectable formation of H_2^(15)N(CO)^(15)NH_2. In the slow-rotation regime, the chemical-shift difference between the protons cis and trans to the carbonyl oxygen decreases rather rapidly with increasing temperature (0.0063 ppm/º). Coupling parameters were extracted from the rather complex six-spin system afforded by H_2^(15)NC(O)^(1)5NH_2. The activation parameters for the rotation in dimethylformamide-dimethyl sulfoxide solution were ΔG^* (245 K) = 11.2 ± 0.3 kcal/mol and E_a = 13.5 ± 0.25 kcal/mol. Significant changes in the sensitivity of the variations of the proton shifts with temperature were found with substitution of deuterium for hydrogen and addition of water to the solvent. The overall results are in accord with the resonance interpretation of the barrier to rotation about the C(O)-N bonds of amides and ureas.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/j100114a013DOIArticle
http://pubs.acs.org/doi/abs/10.1021/j100114a013PublisherArticle
Additional Information:© 1993 American Chemical Society. Received: October 19, 1992. Publication Date: March 1993. This research was supported by the Caltech Consortium in Chemistry and Chemical Engineering; founding members E. I. Du Pont de Nemours and Company, Inc., Eastman Kodak Company and Minnesota Mining and Manufacturing. Additional support was provided by Caltech Summer Undergraduate Research Fellowships (SURF).
Funders:
Funding AgencyGrant Number
E. I. du Pont de Nemours and CompanyUNSPECIFIED
Eastman Kodak CompanyUNSPECIFIED
Minnesota Mining and ManufacturingUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Caltech Consortium in Chemistry and Chemical EngineeringUNSPECIFIED
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Caltech Gates and Crellin Laboratories of Chemistry8751
Record Number:CaltechAUTHORS:20151002-123936293
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20151002-123936293
Official Citation:1.A proton NMR investigation of rotation about the C(O)-N bonds of urea Yiming Zhao, Mary Katherine Raymond, Helen Tsai, and John D. Roberts The Journal of Physical Chemistry 1993 97 (12), 2910-2913 DOI: 10.1021/j100114a013
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60714
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:05 Oct 2015 18:23
Last Modified:05 Oct 2015 18:23

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