| We have found 19F Nuclear Magnetic Resonance (NMR) and Rapid-Injection NMR (RINMR) spectroscopy to be extremely useful in various kinetic and structural studies. Because these played a significant role in the work presented in this thesis, a short, introductory summary along with the results of videographic studies of RINMR mixing are presented in the introduction.;In chapter one, HMPA (hexamethyl phosphoric triamide) titrations were used to characterize the aggregation state of the lithium enolates of several ketones, acetophenone, dibenzyl ketone and phenyl benzyl ketone in ethereal solutions. Mixing studies, other solvent additive titrations (TMEDA, PMDTA, TMTAN), and/or x-ray crystal structures have provided support for the aggregation assignments of these enolates. A new complex ion species was identified and consisted of three enolates connected to a single lithium, (RO)3Li 2-.;Mechanistic studies on the addition of a dimeric and tetrameric enolate to an aldehyde, the aldol reaction, are presented in chapter two. Kinetic evidence was obtained indicating direct reaction of the enolate aggregates in the aldol reaction. The effect of several solvent additives on this addition reaction and the LDA mediated enolization of an unhindered ketone, p-fluoroacetophenone, was examined.;Detailed multinuclear NMR and crystallographic studies of a number of ketone, aldehyde and ester phosphazenium enolates confirmed the "naked" nature of these enolates and are presented in chapter three. In addition, a number of unique homo-hydrogen bonded species were observed for several benzyl carbonyl compounds. In absence of this stabilizing interaction, formation of an isomeric self-aldolate was observed. The nature of the hydrogen bonding interaction of these new homo-hydrogen bonded species and mechanism of the self-aldol condensation was investigated and is presented in chapter three.;In chapter four, the results of RINMR studies to probe the reactivity differences of conformations of Weinreb amides (N-methoxy- N-methyl amides) which result from restricted rotation about the amide bond is presented. One conformation was found to have an increased electrophilicity, presumably due to this conformer's ability to chelate in a bidentate fashion to a cation. As part of this study, the solution structure and the effects of common co-solvents on lithium acetylides was examined. |
