The Synthesis and Study of Polycyclic Aromatic Systems

Fell, Gordon Stephen (1960) The Synthesis and Study of Polycyclic Aromatic Systems. PhD thesis, University of Glasgow.

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To suggest that in certain polycyclic aromatic hydrocarbons, the pi -electrons are not generally delocalised,but are confined to certain 'benzenoid rings' in aromatic sextets, may be at variance with generally accepted modern chemical theory. This concept can nevertheless provide a satisfactory basis for the discussion of the chemistry of these substances. Indeed the remarkable properties of the fully benzenoid hydrocarbons,where the localisation is thought to be complete and the hydrocarbons can be written as condensed polyphenols,must be difficult to account for in a conventional manner. The ideas described above emphasise the fundamental importance of Robinson's "aromatic sextet" to all aromatic substances. In the first section the synthesis of 4,5:12,13-dibenzoheptazethrene is described. The unusual basicity of this hydrocarbon illustrates the tendency for all polycyclic hydrocarbons to adopt configurations which have the maximum number of benzenoid rings. The synthesis of tetrabenzoheptacene has been achieved and this hydrocarbon exhibits all the remarkable stability of all the fully benzenoid hydrocarbons in spite of the extended nature of the molecule. The structure of the tetrabenzoheptacene was fully confirmed by a study of its ultra-violet,infra-red,and phosphorescence spectra. Dihydro-5,6:13,14-dibenzoheptazethrene has been synthesised by three different routes,but could not be dehydrogenated to the fully aromatic system. The apparent instability of the 5,6:13,14-dibenzoheptazethrene molecule is explained in terms of the benzenoid ring theory. Tetrabenzocoronene was synthesised and the absorption spectrum recorded. A study of this,and the properties of the hydrocarbon suggest that this molecule may be sterically strained. Investigation of the little known chemistry of peropyrene was carried out during unsuccessful attempts to synthesise 5,6 benzoperopyrene. A new route to peropyrene was discovered and several derivatives of the hydrocarbon described. 5,6 :2,13-Dibenzoperopyrene was resynthesised by an unambiguous route and its absorption spectrum recorded. The highly condensed green hydrocarbons resulting from the condensation of anthanthrone were investigated. A separation of the substances was achieved and their absorption spectra recorded. Structures have been suggested,but not proven,for these highly complex hydrocarbons. In Appendix A an attempt to synthesise the highly basic dinapthoazulene is described. Finally in Appendix B some preliminary experiments to synthesise a molecule,which must have 'Dewar' structures, are outlined.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1960
Depositing User: Enlighten Team
Unique ID: glathesis:1960-79331
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2020 10:43
Last Modified: 05 Mar 2020 10:43

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