ISSN:
0749-1581
Keywords:
1H NMR
;
13C NMR
;
1-Aza-cyclooctane-2-one
;
Enantholactam
;
Conformation
;
Dynamic NMR
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The conformational properties of enantholactam (1-azacyclooctane-2-one) in solution were studied by 1H and 13C NMR at various temperatures. Only the cis-isomer is present and it occurs in two different conformations in the ratio 3:2, as observed by 13C NMR at - 133°C. In the temperature range - 50 to - 140°C, two conformational processes were observed. A low energy process was visible in both the 1H and the 13C NMR spectra with coalescence temperature ca. - 110°C and a free energy of activation of 30 kJ mol-1, identified as interconversion between the two conformations. A higher energy process was visible in the 1H but not in the 13C NMR spectrum with coalescence temperature ca. - 96°C and free energy of activation 35 kJ mol-1. This process was identified as geminal 1H exchange. A conformational interconversion scheme for partial and full site exchange of protons and carbon atoms, explaining the variable-temperature NMR results, is proposed.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260310912
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