Investigation into the nature of complexes formed between organic acids and bases in aprotic solvents

Abstract

The work described in this thesis consists of an investigation into the nature of the complexes formed between organic acids and bases in aprotic solvents. The physical techniques employed were dielectric constant measurement and nuclear magnetic resonance (n.m.r) respectively.The first section of the thesis consists of a summary of the properties of hydrogen-bonded systems and of the theories concerning the nature of the hydrogen bond.The second section deals firstly with the methods based on dielectric constant determination which have been used for the simultaneous determination of association constant and dipole moment of these complexes. This is followed by an account of the determination of both association constant and dipole moment of several complexes of acetic acid with heterocyclic bases. This work was carried out with the object of establishing: (i) Whether or not there exists a valid method for the simultaneous determination of association constant and dipole moment from dielectric constants. (ii) Whether or not the dipole moment change in the components on complex formation can be found with sufficient accuracy to throw light on the nature of the bonding between acid and base. Computer programs were developed to assist the determination of both association constant and dipole moment. This technique is particularly helpful in cases where one of the components of the mixture is strongly self-associated, but should be of general use. The results suggested that little charge transfer accompanied hydrogen bond format ion.The third section consists of an account of the n.m.r. spectra of acetic acid dissolved in benzene, cyclo-hexane and several heterocyclic bases. The results were consistent with the view that little charge transfer is associated with the hydrogen bonding between acetic acid and those bases.