Graphical method for the determination of the complex NMR shift and equilibrium constant for a hetero-association accompanying self-associations

Abstract

We describe a novel graphical method which, in conjunction with the previously proposed graphical determination of mono;ner shift, dimer shift, and dimerization constant for self-association, allows us to determine the complex shift and equilibrium constant for a hetero-association, A + B reversible arrow AB, accompanying self-associations, A + A reversible arrow A(2), and B + B reversible arrow B-2. The merit of the new method includes the removal of the restrictions imposed on the conventional Benesi-Hildebrand (B-H) plot: (1) that the concentration of one component must be much less than that of the other; (2) that there be no accompanying self-association, The simultaneous equilibrium of the self-association of 2-pyrrolidone (A) and that of 4-methyl-alpha-pyrrolidone (B) and the hetero-association between A and B in acetonitrile-d(3) at 25 degrees C is studied. The inappropriateness of the B-H plot in dealing with this case is also pointed out.