Rate constants and mechanisms for reactions of carbenes and cations from oxadiazolines and other precursors

Abstract

<p>The doctorate work presented is in the area of physical organic chemistry and has involved the study of reactive intermediates. Various oxadiazolines (A ) have been prepared as photochemical and thermal precursors for the study of dialkoxycarbenes (C ), dialkylcarbenes ( D ), as well as alkanediazonium ions (E ), and carbocations (F ) derived from them.* Intramolecular rearrangement reactions were studied in several dialkylcarbenes, and in the excited states of their precursors using both steady-state and laser flash photolytic techniques. Rate constants for both intra- and intermolecular reactions of dialkylcarbenes were determined. Alkanediazonium ions (E ), the conjugate acids of diazoalkanes (B ), have been implicated in the carcinogenicity and mutagenicity of N-alkyl-N-nitroso compounds. Work described within has involved exploratory photochemistry of oxadiazoline precursors in acidic media. Rate constants of proton transfer reactions to diazoalkanes, generated from oxadiazoline precursors, were determined and the sensitivity of these reactions towards acid strength have been evaluated. Methodology for estimating lifetimes and determining the reactivity of alkanediazonium ions and dialkylcarbenium ions using laser flash photolytic techniques has been developed using novel probe reactions. Conclusions about how these reactive intermediates alkylate DNA (which leads to the development of cancer) have been drawn. Preparation of the oxadiazoline precursor to methoxytriphenylsiloxycarbene (C , R1 = CH3 , R2 = SiPh 3 ) was accomplished. The 1,2-silicon migration from oxygen to carbon as well as the competitive extrusion of CO in methoxytriphenylsiloxycarbene were studied. The reactivity of dimethoxycarbene (C , R1 , R2 = CH3 ) toward polychlorinated olefins was also studied. Products of SN 2 displacement of chlorine as well as additions to carbonyl moieties were discovered, the structures of these products were elucidated using a variety of spectroscopic techniques as well as x-ray crystallography in some cases, and mechanisms for their formation proposed. *Please refer to dissertation for diagram.</p>