Hydrogen-bonding and halogen-arene interactions
Dominelli Whiteley2017.pdf (20.15Mb)
Dominelli Whiteley, Nicholas
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Non-covalent interactions are fundamental to molecular recognition processes that underpin the structure and function of chemical and biological systems. Their study is often difficult due to the interplay of multiple interactions and solvent effects common in complex systems. Herein, chapter one provides some general background on the area before presenting a literature review of key, contemporary developments on the use of folding molecules for the quantification of non-covalent interactions. Chapter two investigates the magnitude and extent of energetic cooperativity in H-bond chains. Utilising supramolecular complexes and synthetic molecular torsion balances, direct measurements of energetic cooperativity are presented in an experimental system in which the geometry and number of H-bonds in a chain were systematically controlled. Strikingly, it was found that adding a second H-bond donor to form a chain can almost double the strength of the terminal H-bond, while further extension had very little effect. Computations provide insights into this strong, short-range cooperative effect in a range of H-bonding contexts. Chapters three and four build on the concepts and molecular models discussed in chapter two. Chapter three discusses the effects of interplay and competition between strong H-bond acceptors such as formyl groups and the weaker organofluorine H-bond acceptor. There has been some debate in recent literature about the latter’s ability to accept H-bonds, the work presented shows that although organofluorine is a weak H-bond acceptor, it can have a significant modulating effect on stronger interactions when in direct competition. Chapter four investigates deuterium isotope effects on conformational equilibria governed by non-covalent interactions. The results show that any deuterium isotope effect which exists is less than the margins of experimental error. Finally, chapter five discusses a molecular torsion balance designed to investigate halogen∙∙∙arene interactions. The interaction energies were investigated in a range of solvents and mixtures in order to dissect out the dispersive and solvophobic components of folding. Overall, these interactions were found to be weak. Nonetheless, a model was used to dissect trends in solvophobic and electronic contributions to the binding using multiple linear regression based upon the cohesive energy density and polarisabilities of the solvents.