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

Abstract

A novel graphic method to determine the complex shift and equilibrium constant for a hetero-association, A + B ⇌ AB, accompanying a self-association A + A ⇌ A₂ has been described. The method is to be used in conjunction with a graphic determination of the monomer shift, dimer shift and dimerization constant proposed previously. Our new method is advantageous over the conventional Benesi–Hildebrand (BH) plot in that the limitations, (1) that the concentration of one component must be much less than that of the other and (2) that self-association of species is not allowed, are completely removed. The related parameters of the self-association of 2-isopropylphenol (A) and the hetero-association of 2-isopropylphenol with acetone (B) in the inert solvent [²H₁₂] cyclohexane has been used to demonstrated the use of this new graphic method. Comparison with the results from a BH plot has also been made.