Methoxy group conformation effects on 13C NMR parameters in 1‐cis‐methoxy‐ and 1‐trans‐methoxy‐1,3‐trans‐butadiene
The proton‐coupled 13C NMR spectra of 1‐trans‐methoxy‐ (2) and 1‐cis‐methoxy‐1,3‐trans‐butadiene (3) are consistent with a methoxy heavy atom planar conformation with s‐syn and s‐anti orientations, respectively. Ab initio 6–31G* calculations confirmed such conformations. They were taken as model com...
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| Autores principales: | , , , , |
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| Formato: | JOUR |
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_07491581_v32_n4_p199_Esteban |
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| Sumario: | The proton‐coupled 13C NMR spectra of 1‐trans‐methoxy‐ (2) and 1‐cis‐methoxy‐1,3‐trans‐butadiene (3) are consistent with a methoxy heavy atom planar conformation with s‐syn and s‐anti orientations, respectively. Ab initio 6–31G* calculations confirmed such conformations. They were taken as model compounds to determine the influence of electrostatic interactions on the methoxy 13C NMR parameters. A shielding increase of 4 ppm is observed in 2, with respect to 3, for the OMe 13C chemical shift in an s‐syn conformation and is ascribed to the attraction between the methyl and vinyl moieties as proposed by Li and Chesnut. The methyl 1J(C,H) coupling is not affected by this interaction, showing that the carbon 2p electrons are more polarizable than those in the 2s orbital. Copyright © 1994 John Wiley & Sons Limited |
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