Etude de la structure et de la reactivite d'ethers d'enol par utilisation d'un reactif de deplacements chimiques et mesures d'effets overhauser nucleaires en rmn 1H

Abstract

Resume Complexation of enol ethers derived from styrene with the lanthanide chelate: Eu(DPM)3 is reported. The geometry of the complex formed by α methoxy-ββ dimethylstyrene and Eu(DPM)3 is determined: the methoxy and phenyl groups are largely out of the plane of the double bond in the complexed enol ether, respectively 75° and 60°. The phenyl conformation group and its “ring current” effect are in agreement with the values of the chemical shift difference between the two signal resonances of the ββ methyl groups for the free molecule. The reactivity of ten enol ethers towards Eu(DPM)3 is studied and is interpreted in terms of the relative basicity of the OCH3 groups of these compounds. The basicity of the oxygen atom in the OCH3 groups is a probe of the degree of conjugation with the double bond and gives informations about the conformations of the OCH3 groups: e.g. in the plane or out the plane of the double bond. In the case of the in plane conformations, utilisation of nuclear Overhauser effect is employed to distinguish between the s-cis and the s-trans conformations. These conclusions are in agreement with previous results on these compounds, obtained by 13C NMR.