Abstract

The recent interest in non-covalently stabilized molecular assemblies has led to the creation of the field of supramolecular chemistry . This thesis is concerned with the effects of supramolecular (host-guest) binding on organic reactivity. Of particular interest is the catalysis of organic reactions brought about by transition state stabilization , which arises from the binding of substrates (guests) relative to the strength of binding of the transition states to catalytic hosts such as cyclodextrins and micelles. In effect, the work of this thesis is concerned with the origin of supramolecular catalysis . The first area of research discussed in the thesis exploits the principles of supramolecular chemistry (Chapter I, Section 1.1) and hydrophobic effects (Chapter I, Section 1.3) to investigate cyclodextrin-guest inclusion complexes (Chapter II). The effects of cyclodextrins on the reactivity of acid-catalyzed hydrolysis of two acetals and an orthobenzoate in the presence of added ketone guests were studied (Chapter III) as part of a search for improved methods of accurately determining the strength of complexation between cyclodextrins and various guests (eg. ketones). It was shown that inhibition kinetics can be employed as a fast reliable methodology to determine the dissociation constants of β-cyclodextrin-ketone complexes under certain circumstances. The second area of research, which constitutes the bulk of the work in the thesis, focussed on micelles (Chapter IV) and their catalytic effects on bimolecular ester cleavage reactions from the perspective of transition state stabilization (Chapter I, Section 1.2). The work was initiated after previous research on the alkaline hydrolysis of aryl esters in cetyltrimethylammonium bromide (CTAB) micelles (Chapter V). In those studies it was shown that aryl ester binding to CTAB micelles is independent of the aryl group but it depends on the hydrophobicity of the ester chain. The magnitude of catalysis is, however, independent of the ester chain. Following these intriguing results, and in order to clarify the misconceptions about the mechanism of the catalysis by the micelles, it was decided was to investigate the effects of CTAB micelles on ester cleavage by other nucleophiles. Firstly, the thiolysis of p -nitrophenyl alkanoates (acetate to decanoate) in CTAB micelles was studied (Chapter VI). Secondly, the aminolysis of p -nitrophenyl esters by neutral amines (mainly n -alkylamines) in CTAB micelles was studied (Chapter VII). Finally, a study of the cleavage of pNPA and pNPH by amino acid anions (AA - ) in CTAB micelles demonstrated that a threshold hydrophobicity dictates the partitioning and binding of the AA - to the CTAB micelles (Chapter VIII). (Abstract shortened by UMI.)