Stereoelectronic effects in cyclic sulfoxides, sulfones, and sulfilimines: application of the Perlin effect to conformational analysis |
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Authors: | Wedel Tobias Müller Monika Podlech Joachim Goesmann Helmut Feldmann Claus |
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Institution: | 1. Institut für Organische Chemie der Universit?t Karlsruhe (TH), Fritz‐Haber‐Weg 6, 76131 Karlsruhe, Germany, Fax: (+49)?721‐608‐7652;2. Institut für Anorganische Chemie der Universit?t Karlsruhe (TH), Engesserstrasse 15, 76131 Karlsruhe, Germany |
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Abstract: | The 1JC--H coupling constants in conformationally constrained sulfoxides, bissulfoxides, sulfoxide-sulfones, and sulfilimines derived from 2-benzylidene-1,3-dithiane and 2-(2,2-dimethylpropylidene)-1,3-dithiolane were measured by means of HMQC and HSQC NMR experiments and the Perlin effects were calculated. The type and the relative configuration of S==X groups (X= O, NTos) in these compounds have a strong influence on the magnitude of coupling constants for axial and equatorial C--H bonds, respectively. Axial S==O bonds give rise to a stereoelectronic effect on antiperiplanar axial C--H bonds. The resultant weakening of the respective C--H bonds leads to a smaller coupling constant than for a respective equatorial C--H bond. Equatorial S==O groups have an influence on beta-C--H bonds through a homoanomeric effect. Here, the axial C--H bond is weakened and a smaller coupling constant is measured. Sulfilimine groups show similar effects to sulfoxide groups. |
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Keywords: | C‐H coupling constants heterocycles hyperconjugation NMR spectroscopy Perlin effect sulfur |
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