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The alkali cation effect on the 1 H NMR chemical shifts of the indenyl carbanion
Author(s) -
Gooijer C.,
Velthorst N. H.
Publication year - 1979
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270121207
Subject(s) - chemistry , carbanion , chemical shift , lithium (medication) , ion , dimethoxyethane , alkali metal , proton , nuclear magnetic resonance spectroscopy , stereochemistry , organic chemistry , medicine , physics , electrode , quantum mechanics , electrolyte , endocrinology
The complex character of the temperature dependence of the 1 H NMR chemical shifts of indenyl‐lithium and ‐sodium in dimethoxyethane is explained. It is shown that the cation causes a polarisation of the CH 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 13 C NMR chemical shift data. By subtracting the temperature dependent contribution of the indirect effect from the experimental 1 H data, the direct effect is visualised. It appears that information on ion paris obtained by 1 H and 13 C 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.