1702
LUTHERE, ERLCKGQX AND R. A. ALBERTY
Vol. 66
EVIDENCE FROM NUCLEAR MAGSETIC RESOSANCE FOR HALATE COMPLEXES OF ALKALI METAL CATIONS BY
LUTHERE. ERICKSON
AND
R. A.
hBERTY
Department of Chemistry, University of Wisconsin,Madison, Wisconsin Recezuad A ~i l I4, I968
A pronounced concentration dependence is observed in the high-resolution proton n.m.r. spectra of DzO solutions of all five of the alkali metal malates. By contrast, the spectrum of tetramethylammonium malate is independent of concentration. These observations suggest that there is appreciable ion association in the alkali metal malate solutions. From the magnitude of the concentration effects on spin-spin coupling constants and chemical shifts, the dissociation constant of the complex, CM- (where C is any alkali metal ion), is estimated to be about 10 M .
Introduction The great sensitivity of n.m.r. chemical shifts to molecular environments provides still another method for determining the nature of the ionic species present in aqueous solutions. Li, Johnson, and Shoolery2 recently reported that added ZnClz or MgC12 produced a decrease in the CH2 proton chemical shifts of glycylglycinate and glycineamide in D20 solution. The magnitude of the effect is greater for Zn+2 than for Mg+2 and apparently is closely related to the relative stabilities of the corresponding complexes formed between the metal ion and the proton-containing ligand. The striking dependence of the F19chemical shifts of AlF+2 and AIFz+on Na+ and I
