An N.M.R. Spectroscopic Investigation of Molecular Interactions in Solution

Abstract

Whilst molecular complex formation in aromatic solvents has been studied by nuclear magnetic resonance for many years, and much useful information has been obtained, a number of problems associated with these studies remain unresolved. The most important of these may be summarized as: a) which of the three concentration scales in current use (namely mole fraction, molarity and molality) give equilibrium quotient and excess shielding values which are independent of the data evaluation procedure used, b) which data evaluation techniques give thermodynamically valid results which are independent of the nature of the inert solvent used and the particular composition of the systems measured, c) are any of the solvents and references used inert and hence non-complexing with aromatics, and d) what is the effect of substituents, on the aromatic solvents, on the type of complexes formed. The work reported in this thesis is directed towards resolving these problems. The following conclusions are obtained: a) if a correction is made for the difference in the molar volumes of the aromatic and inert solvents and if the double reciprocal plot devised by Benesi and Hildebrand is used then thermodynamically valid results are obtained using the mole fraction concentration scale, b) thermodynamically valid results are only obtained on the molarity scale if the limiting slope of the BH plot is used, c) cyclohexane is believed to be a genuinely inert solvent and a suitable reference material, but both carbon tetrachloride and tetramethylsilane interact with aromatic molecules, and d) chlorine substituents on an aromatic ring appear to alter the characteristics of the aromatic molecule sufficiently to enable an n-type complex to be formed in addition to the expected π-complex. Finally, during these investigations the variation of the combined anisotropy and dispersive medium screenings [please see Thesis]  of mixtures with composition are shown to be related to the thermodynamics of perfect and imperfect mixtures,