Evaluation of the association constants of molecular complexes by electronic and NMR spectroscopy - First evidence for association constants measured by NMR spectroscopy being independent of the methods used

摘要

Modified Benesi-Hildcbrand and Hanna-Ashbaugh equations have been used for the evaluation of association constants of the charge-transfer complexes by electronic spectroscopy and NMR spectroscopy, respectively. Association constants of charge-transfer complexes of aniline with various dinitrobenzenes have been calculated by electronic spectroscopy using the existing methods and compared with those calculated by the new method. Results show that the new equation has the advantages of measuring K directly rather than evaluating it from the product Ke leading to increased accuracy and being obeyed in cases where Foster-Hammick-Wardley and Scott equations fail. Similarly, association constant of dinitrotoluene-diphenylamine charge-transfer complex has been calculated by NMR spectroscopy using the existing and the new equations. Values of K measured by NMR spectroscopy using different methods are nearly the same, a fact not borne by other workers. This is perhaps the first report where equal values of K are obtained by different methods. The modified Hanna-Ashbaugh equation also has the advantage of measuring K directly without recourse to evaluating it from the product KΔ_0.