Recherches sur la stéréochimie des diènes fonctionnnels—XI: Interprétation théorique des déplacements chimiques de stéréoisomères D'éthoxybutadiènes-1,3

A theoretical analysis of the proton chemical shifts of alkoxy-1,3-diene stereoisomers is proposed. The diamagnetic contribution is calculated from π and σ theoretical indices obtained by the CNDO/2 method. This effect depends on the stereochemistry of the molecule and the charges and chemical shifts alternate in the same way. The diamagnetic part is often small compared to the experimental value, however, and the paramagnetic contribution Δδ_p is important. Δδ_p is difficult to explain with the usual models of anisotropic and electric contributions, but the results give useful information on the conformations of the molecules.