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Title: Formation, decomposition and isomerisation of protonated molecules in the gas phase
Author: Anderson, P. D. J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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Pulsed high pressure source mass spectrometry has been used to investigate gas phase proton transfer reactions and the reactivity of gas phase protonated molecules. Proton transfer reactions involving substituted benzaldehydes, where protonation takes place on the aldehyde substituent, were studied in order to investigate their reactivity in relation to previous proton transfer measurements involving aromatics, which protonated on the ring, which showed some unusual behaviour. Gas phase stabilities were obtained in the form of proton affinities which were then compared with the results of semi-empirical molecular orbital calculations (MNDO) and with solution based σ+ substituent constants. Good correlations were observed and five new experimental proton affinity values were obtained. A study to examine thermal pyrolysis of protonated molecules was initiated on the basis of previous work which indicated this type of reaction behaviour to be occurring. The study did not yield any firm evidence to show pyrolysis to occur in the systems examined but instead highlighted numerous problems associated with the techniques for studying this process, which indicates that processes reported in the literature may not be correct. Other interesting reactions were observed and kinetic information obtained. The mechanisms of protonation at different sites on chlorobenzene has been studied in detail by tandem mass spectrometry/collision induced decomposition experiments. These showed that, when cold, the neutral molecule could be protonated on the thermodynamically unfavoured Cl atom. At higher temperatures it was shown that a degree of protonation occurs at the ortho- ring site in addition to the more stable para- ring position. It was possible to estimate the energies of these thermodynamically unfavoured sites, the significance of these values being that they represented the procurement of proton affinities of high energy sites by a new method.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available