7Li, 23Na and 9Be nuclear magnetic resonance investigations of the influence of N-substitution on the solvation interaction of amides with alkali and alkaline earth metal ions

Abstract

⁷ Li, ⁹Be and ²³Na chemical shifts of metal salt solutions in formamide and its mono- and di-N-substituted derivates have been investigated in order to obtain information about the influence of N-methylation and N-ethylation on the interaction of the amide group with alkali and alkaline earth metal ions. Concerning the interaction with Li⁺ and Na⁺ ions, methyl and ethyl substitution were found to have an opposite influence on the shifts, whereas in the case of Be²⁺ ions all kinds of substitution shift the resonance signal towards higher field. Quantum chemical calculations with minimal Gaussian basis sets were employed in order to obtain some additional information about the background of the substituent effects and the exceptional line broadening observed for the metal ion solvates with diethylformamide. The results are discussed with respect to reported relations between metal resonance shifts and the donor abilities of the solvents.