Hydrogen bonded anions

Doctoral thesis English OPEN
O'Shea, Terence Anthony
  • Subject: QC | QD

The work recorded in this thesis can be divided into three sections. The first section (chapter three) is concerned with essentially weak H-bonded anions of the type XH(02CR)-, where X- is a group 7 halide ion, and R is H, CH3, CF3 or CHC12. The IR spectrum of each of the se anions has been examined and complete assignments have been made in most cases. The relationships which exist in the series, whichare a direct result of their chemical similarities, are discussed in terms of the pKa values of the acid and base concerned.\ud \ud The second section (chapter four) deals with Type B hydrogen dicarboxylate salts of acetic acid and its halogenated derivatives. Their IR spectra have been examined at the temperature of liquid nitrogen and assignments have been made. The importance of low isotopic shifts is discussed and used as evidence for asymmetry in the potential energy surface of the proton. Secondary evidence from other techniques, viz. NQR, inelastic neutron scattering, Raman and Far IR spectroscopy, has been obtained which parallels and mconfirms the results from IR spectroscopy.\ud \ud Type A salts, which are thought to be examples of symmetric H-bonds, have been examined by the same techniques which were used for Type B salts. In particular their IR spectra have been examined and assigned for the first time. Attention is drawn to the low frequency of~OH and~OD, and to its high isotopic shift. The IR spectrum of Potassium hydrogen diaspirinate has been recorded, but not analysed in detail, and it is clear that it is similar to the much simpler IR spectrum of the Type A salts prepared in this work. The latter example represents a case where very recent and accurate neutron diffraction data is available and where it was suggested that ~OH is below l000cm. This evidence, together with work on Type A and B salts, has led to an idea of the shape of the potential energy well for the proton and deuterium in Type A salts which is based on a symmetric double minimum. A similar situation is suggested for the proposed symmetric cases of HC12-, and the differences from the HF2- system is made apparent in the text.
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