Optimising Stable Radicals for the Electrochemical Generation of Reactive Intermediates

Abstract

This thesis concentrates on the electrochemical activation of stable-radical adducts to generate reactive intermediates for small molecule and polymer chemistry. The majority of this work concerns the computational modelling and design of such compounds using high-level, ab inito quantum chemistry methods. The main findings are as follows. It is first shown that adducts based on highly-stable Blatter and Kuhn-type radicals undergo mesolytic cleavage upon one-electron oxidation, generating reactive carbocations or carbon-centred radicals. Substituent effects are employed to optimise this chemistry, either to reduce the oxidation potential of the adduct to favour the production of radicals, or by altering the bond-dissociation free energy of mesolytic cleavage to control the rate of fragmentation. Computational chemistry is then used to explore the scope for stable-radical adducts as electrochemically activated alkylating agents. SN2-type methylations of pyridine are studied over a broad range of nitroxide, triazinyl, and verdazyl-based adducts (X-Me). Here, high oxidation potentials are found to render low SN2 barriers to methylation and thus more reactive agents, highlighting the suitability of commercially available, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), in this role. Modelling is also applied to study the triboelectrification of polymeric insulators. Here, material-specific charging properties and dissipation rates are found to be connected to the stability of anionic polymer fragments to oxidation, and cationic fragments to reduction. Computational methods are then used to study the low-frequency (Terahertz) vibrations in molecular crystals. A method benchmark is presented - identifying parameters that reliably produce accurate simulated spectra - along with several new analytical tools built for the assessment of spectral data. Show more