| Abstract: | The complex character of the temperature dependence of the 1H NMR chemical shifts of indenyl-lithium and -sodium in dimethoxyethane is explained. It is shown that the cation causes a polarisation of the C? H bonds and thus influences the proton shifts of the anion, both directly by its electric field along the bonds (the direct effect) and indirectly via its effect on the π-electron distribution (the indirect effect). The indirect effect is inferred from 13C NMR chemical shift data. By subtracting the temperature dependent contribution of the indirect effect from the experimental 1H data, the direct effect is visualised. It appears that information on ion paris obtained by 1H and 13C NMR on the one hand and optical spectroscopy on the other hand is complementary. Apparently, aggregation of ion pairs does not seriously affect the chemical shift data. |
