Molecular complexes. Part 8.—Rationalization of the use of the molal scale for processing nuclear magnetic resonance data

Abstract

It is shown that when based on the common definition of molality, the equilibrium quotient K_m for a reaction A + B⇌A⋯B occurring in an inert solvent S will vary with the concentration of the components and with the nature of S. If this molal scale is employed with the Benesi–Hildebrand equation to process chemical shift data it is shown that the value obtained for Δ^m_c, the chemical shift difference between “free” and fully complexed A, is quite different from that derived using the mole fraction and molar scales. The reasons for this are explained, and a molal based procedure for processing data is described which results in values for Δ^m′_c and K_m′, which are compatible with the molar and mole fraction values.