Electron Impact Studies on Halogen Containing Molecules

Snedden, Walter (1959) Electron Impact Studies on Halogen Containing Molecules. PhD thesis, University of Glasgow.

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The work described in this thesis has been divided into three sections, namely: 1. "The Latent Heat of Sublimation of Carbon and the Heat of Dissociation of Nitrogen." 2. "The Mass Spectra of Camphor and Some of its Halogen Derivatives." 3. "Electron Impact Studies on some Chlorinated Benzaldehydes." In Section 1 a study of the ionization and dissoc-riation of the molecules CX4 (X = F,Cl,Br); CHX3, CH2X2, CH3X (X = Cl,Br) and NH3 was undertaken. Appearance potentials of some of the positive ions produced under electron bombardment were obtained for each compound, while a suitable method was devised for the generation of some of the corresponding free radicals and the measure-sment of their ionization potentials. Dissociation processes were then selected to account for the formation of each ion. Combination of the experimental data in the appropriate equations then gave a series of bond dissoc-siation energies from which the heat of atomization of each compound was obtained. Substitution of this heat of atomization in a suitable thermochemical cycle then all:owed a value for the latent heat of carbon (Lc) or the heat of dissociation of nitrogen, D(N2), to be estimated. Prom the results it was concluded that Lc = 7.386 eV., and D(N2) = 9.756 eV. are most likely to be correct. In Section 2, the "Cracking Patterns" of camphor, alpha-bromo-, alpha-chloro-, beta-bromo-, beta-iodo-, alpha:alpha-dibromo- and alpha:beta-dibromo camphors are recorded. An attempt was then made to explain the occurrence of the principal peaks of each spectrum in terms of the current theories of the origin of mass spectra and to interpret the differences in the spectra of the seven compounds with the variation in molecular structure. This has been fulfilled with some modicum of success. Plausible mechanisms, based on such generalizations as facile allylic bond fission, ready elimination of CO and the occurrence of rearrange:ments promoted by the relative stabilities of the fragment ions, have been proposed for the production of the more prominent ions observed. It is emphasized that the results of the present work can only give an indication rather than a conclusive proof of the behaviour of the camphor skeleton under electron impact. In Section 3, the appearance and ionization potentials of some of the ions produced in the electron impact induced dissociation of o-, m- and p- chlorobenzalde-:hydes are recorded. The dissociation energies of the bond between CHO and the aromatic nucleus, D(Ar-CHO), was measured in each case, and compared with that of benzaldehyde itself. It was then possible to interpret the results in terms of the Inductive and Conjugative effects of the substituent chlorine atom. The dissociation energies of the corresponding bond in the molecule ion, D(Ar+-CHO), were also obtained. The relationship between D(Ar-CHO) and D(Ar+-CHO) was discussed, resulting in the tentative proposal that a benzaldehyde type molecule ion may undergo ring expansion to give an ionized derivative of tropone.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Molecular chemistry, Physical chemistry
Date of Award: 1959
Depositing User: Enlighten Team
Unique ID: glathesis:1959-79346
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2020 10:39
Last Modified: 05 Mar 2020 10:39
URI: http://theses.gla.ac.uk/id/eprint/79346

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