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Methoxy group conformation effects on 13C NMR parameters in 1-cis-methoxy- and 1-trans-methoxy-1,3-trans-butadiene

✍ Scribed by Angel L. Esteban; Maria P. Galache; Ernesto Diez; Rodolfo R. Biekofsky; Rubén H. Contreras

Publisher
John Wiley and Sons
Year
1994
Tongue
English
Weight
557 KB
Volume
32
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

The proton‐coupled ^13^C 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 ^13^C NMR parameters. A shielding increase of 4 ppm is observed in 2, with respect to 3, for the OMe ^13^C 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 ^1^J(C,H) coupling is not affected by this interaction, showing that the carbon 2p electrons are more polarizable than those in the 2s orbital.

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