A Theoretical Approach to Aromatic-Radical Interaction

• Main Author: Howard-Jones, Helen Mary
• Published: Bangor University 2006
• Subjects: 540
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485125

This thesis describes work conducted towards the design and implementation of suitable models to describe accurately aromatic radical systems and the stabilising non covalent interaction with the radical. The DFT methodologies, B3LYP, BH&HLYP and B3PW9l have been implemented throughout this work as a result of an extensive trail. A key finding was the identification and elucidation of the C6H6/Cr radical complex its properties and thermochemical data. The most stable structure of this complex was identified as a hybridised intermediate cr-n-complex. This non covalent complex possesses charge transfer character, where the Cl· is positioned approximately 2.5A from the aromatic ring. The optimised model for this structure was further employed as a blueprint model for the design and analysis of other aromatic-radical systems. Throughout the analysis of other Ar-radical complexes theoretical DFT calculations predict the most stable geometry is one which mirrors the C6HJCl· radical complex. The solvent effect on the C6HJCl· radical complex in the hydrogen abstraction reaction of alkanes has also been examined. These processes are currently not widely understood. Methane, ethane, propane and I-butane have been modelled with the reaction of the C6HJCr complex and the un-complexed chlorine radical. DFT calculations predict an endothermic pathway for the reaction of cr with primary hydrogens. An exothermic pathway is predicted for the reaction with secondary and tertiary hydrogens. The predicted stabilities of the transition states from these reactions in the presence of the aromatic moiety are greatly enhanced. It is clearly seen that the presence of the benzene moiety distinctly facilitates the selectivity of tertiary hydrogen abstraction.