O-17 NMR-SPECTRA AND CONFORMATION OF CYCLIC VINYL ETHERS

The O-17 NMR spectra of a number of heterocyclic vinyl ethers were recorded in CDCl3 and DMSO-d(6) solutions. The oxygen chemical shifts reveal substantial differences in the strength of p-pi conjugation between the five- and six-membered ring compounds, especially between those with an exocyclic C=C bond. The conformations of the title compounds were estimated by force-field calculations; the calculated torsional angle of the C-O-C=C moiety appears to be a linear function of the O-17 NMR Shift data, corrected by appropriate structural factors.