Searching for mechanistic insights in complex reaction pathways

Student thesis: Doctoral Thesis

Abstract

In order to further advance chemical reactions, understanding the mechanism underpinning complex reaction pathways is key. This is the overarching aim of the work contained in this thesis, and through the application of density functional theory calculations four different systems are studied.Investigation of the mechanism of 1,2,4-triarylbenzene formation from 1,3-diaryl-2-propen-1-ols as proposed by Ghorai et al.1 demonstrates that the phenyl anion can be a competent leaving group. The implications of this study are that simply considering the pKa of the leaving group’s conjugate acid does not afford a reliable prediction, for when the choice of leaving group is hydride or phenyl anion - the phenyl anion wins. Such a leaving group would not be predicted to be competent by the simple consultation of a pKa table, and this opens further possibilities of bad leaving groups made good.Competing reaction pathways are an inherent part of complex reaction systems; as such it is no surprise that in order to gain mechanistic insights into the reducing abilities of the Stoltz-Grubbs reducing system two competing reduction mechanisms were investigated. Through calculations it was possible to determine that the hydride and single electron transfer mechanisms were indeed not competing but were individually active for different types of substrate. Hydride reduction was applicable to the polyaromatic hydrocarbons naphthalene, phenanthrene and anthracene, whilst single electron transfer was deemed responsible for the reduction of N-benzylindole and N-phenyl-N-methylaniline.Time is often key in achieving mechanistic insights for some complex reactions, one such reaction has been shown to be the reduction of benzophenone by KOtBu. Studied initially by Ashby et al.2 in the 1980s this reduction was predicted to occur by electron transfer from KOtBu to benzophenone resulting in the blue coloured benzophenone ketyl. The mechanism behind this reaction has now been uncovered and shown to involve the visible light excitation of a complex between KOtBu and benzophenone resulting in a charge transfer from KOtBu to benzophenone.The homocoupling of benzene under the action of potassium metal and an alkali metal salt was recently disclosed by experimental colleagues in the Murphy Group. A preliminary study of this complex reaction has shown that a further understanding of the composite structures formed upon mixing potassium metal and alkali metal salt is required in order to facilitate meaningful computational studies.
Date of Award26 Sep 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorTell Tuttle (Supervisor) & John Murphy (Supervisor)

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