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Application of 15N spectroscopy and dynamic NMR to the study of ureas, thioureas and their lewis acid adducts

✍ Scribed by M. L. Martin; M. L. Filleux-Blanchard; G. J. Martin; G. A. Webb

Publisher
John Wiley and Sons
Year
1980
Tongue
English
Weight
719 KB
Volume
13
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

Rotational barriers and ^15^N chemical shifts have been measured in a number of ureas and thioureas. As anticipated on the basis of the ^15^N shifts, several previously unobserved rotational barriers could be detected by using lanthanide reagents or a high field spectrometer. Nearly constant effects on both the rotational activation energy and the ^15^N shift are produced on going from ureas to the corresponding thioureas, and correlations are found between the ΔG‡ and δ^15^N values. The results are discussed in terms of lone pair delocalization, and anomalies with respect to the general behaviour are tentatively explained in the light of the effect of steric torsion in crowded structures on the ^15^N shifts and rotation barriers.

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