The interpretation of mass spectra has made great progress over the past decade, as experimental methods have been developed for assigning structures to organic ions in the gas phase. This thesis describes the important experiments in gas phase ion chemistry whose correct interpretation can lead to the assignment of structures, and the elucidation of fragmentation mechanisms of organic positive ions. The low energy fragmentations of five isomeric [H3,C,N,O 2]+· ions. The low energy fragmentation characteristics of the [H3,C,N,O2]+· isomers, H3CNO2+·, 1, H2C=N(O)OH+·, 2, H3CONO +·, 3, HC(O)NHOH+·, 4, and HC(OH)=NOH+·, 5, were studied in detail by metastable ion mass spectrometry. Appearance energy measurements established the potential energy surface of the isomers 1, 2 and 3 showing the intricate interrelation between them. For isomers 4 and 5, it was concluded that they do not intercommunicate with ions 1, 2 and 3 prior to fragmentation. Neutralization-reionization mass spectrometry indicated that the enol form of formohydroxamic acid structures as well as the keto analogue are stable in the gas phase. The neutral counterparts of the C2H7O + isomers. The neutral counterparts of the C2H 7O+ isomers, CH3O+(H)CH 3, CH3CH2OH2+ and C 2H4···H-OH2+ have been studied by means of neutralization-reionization mass spectrometry. It was observed that the internal energy of protonated dimethyl ether ions is directly related to the stability of the neutrals generated by electron transfer, and on their dissociation. With regard to CH3CH 2OH2+ and C2H4···H-OH 2+, it was concluded that the former ion can be obtained as a neutral species in the gas phase, whereas the latter isomer could not be produced as a neutral species. Classical and non-classical forms of the ethyl cation and their participation in the ions RO+(C2H5)R'. Oxonium ions formed via ion/molecule reactions between several oxygen centered molecules and the ethyl cation were studied. Significant H/D mixing in these oxonium ions was observed only when a labeled ethyl cation was reacted with a non-labeled ROR' molecule. The degree of H/D mixing depends only on the size of R and R', being independent of the observational timeframe from 1-30 mus. When non-labeled ethyl cations were reacted with labeled ROR' molecules, H/D mixing was not observed. The results were interpreted as arising from the classical and non-classical forms of the ethyl cation having different reactivities with ethers of different sizes. Homologous hydrogen-bridged intermediates R1R 2O···H···C(O)R3 from ionized beta-hydroxyethers. The unimolecular dissociations of several beta-hydroxyethers and some of their isotopomers were studied by metastable ion and collision induced dissociation mass spectrometry. It was found that molecular ions of the form R1OCH(R2)CH(OH)R 3 yield protonated ethers, R1O+(H)R2 , via intermediates of the type R1R2O···H···C(O)R 3+·.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/10954 |
| Date | January 1992 |
| Creators | Sirois, Martin. |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Detected Language | English |
| Type | Thesis |
| Format | 163 p. |
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