Some studies of donor-acceptor systems and the ortho-parahydrogen conversion on transition metal salts.
thesisposted on 19.11.2015, 08:44 by Mike Farmer
This thesis is presented in two parts. Part one deals with a study of donor-acceptor systems in both the solid and solution phases using spectroscopic techniques and part two contains an investigation of the catalytic properties of the first row transition metal salts towards the ortho-parahydrogen and hydrogen-deuterium exchange reactions. An introduction to donor-acceptor complexes and the theoretical treatments of such complexes has been included. It has been suggested that in solid complexes in which there is a strong donor (D) and strong acceptor (A) of electrons that the neutral species DA and the dative species DA can exist simultaneously. This postulate has been tested using complexes of N,N,N',N-tetramethyl-p-phenylenediamine with a series of strong acceptors and found to be false, and the explanation of why the DA and DA species do not exist together in the solid state is discussed. The use of halogenomethanes as acceptors in donor-acceptor complexes has been examined using aromatic amines and condensed hydrocarbons as donors. The general belief that these "contact" donor-acceptor complexes should give characteristic absorption peaks is criticised. The results obtained show that instead of a new absorption peak characteristic of the complex there is a broadening of one of the donor peaks which could lead to an incorrect interpretation of the spectra. The merits of the Benesi-Hildebrand equation when applied to weak donor-acceptor complexes is discussed with special reference to the role of the solvent in complex formation and an attempt has been made to establish the true nature of the interaction in these donor-acceptor systems. An investigation of the catalytic properties of the first row transition metal divalent sulphates and chlorides to the ortho-parahydrogen conversion using thermal conductivity and mass spectroscopic techniques has shown that the conversion over the temperature range 77-300K is purely physical in nature. The theoretical treatments for this type of conversion are thoroughly discussed and a mechanism for the conversion on the salts examined is suggested. Calculations based on the suggested mechanism have been made and found to favourably fit the experimental results obtained.