NMR study of ε-caprolactam in various solvents. Graphical determination of monomer shift, dimer shift and dimerization constant from the dilution shift data

A graphical method for the simultaneous determination of the monomer shift, dimer shift and dimerization constant of a self-association system from the dilution NMR shift data is proposed. This method avoids the conventional extrapolation to infinite dilution to obtain the monomer shift. Three self-association systems: ε-caprolactam in [2H1]chloroform, [2H6]acetone and [2H3]acetonitrile were studied at various temperatures. The enthalpy and entropy of dimerization were also determined from van't Hoff plots.