Nuclear Magnetic Resonance Studies of Acid-Base Association in Solution. II. Association between Ketones and Tris (dipivaloylmethanato) europium

Association between Eu (dpm)3 and 4-substituted acetophenones or aliphatic ketones has been investigated by measurement of the concentration dependence of 1H chemical shifts. The stoichiometry was found to be 1 : 1 by the Job method, and both the equilibrium constant K1 and the bound chemical shift Δ1 were estimated. K1 values of 4-substituted acetophenones were found to be governed predominantly by the electronic effect, whereas those of symmetrical ketones are controlled by the difference of the standard entropy ΔS° but those of nonsymmetrical ketones are not. These results can be interpreted in terms of the coordination populations of Eu (dpm)3 on the two sites of the carbonyl oxygen. The populations were obtained independently from the ratio of the geometrical factor (3cos2θ-1)/γ3 and from ΔS°, and the results were consistent with each other.