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Theses

Etude de Diradicaux hétérocycliques

Abstract : Diradicals are known to be highly unstable molecules. For example, triplet 1,3-cyclobutanediyls can only be observed in matrices at very low temperature, whilst the corresponding singlet diradicals, formally resulting from the homolytic cleavage of the bridging σ-bond, are predicted only as transition states for the inversion of the corresponding bicylo[1.0.0]butane.
The first part of this manuscript is devoted to the study of diradicals based on main group elements.
The first chapter is a litterature survey, which underlines the role of heteroelements in the isolation of the first localized singlet diradical. The framework of the latter is formed only of boron and phosphorus atoms.
The second chapter focuses on the different isomers of this diradical, and especially its valence isomers. After an introduction to the theoretical concepts, the factors allowing the stabilization of the already known isomers are discussed, and the isolation of new isomers is described.
The third chapter describes the bond-stretch isomerism. In our case, two isomers which only differ by the length of one bond are in equilibrium in solution. Variable temperature NMR experiments were performed to study the influence of the electronic factors involved in this equilibrium.
This work led us to consider the preparation of an organic diradical formed of second row elements: carbon and nitrogen. This was the starting point for the development of a novel synthesis of iminium and imidazolinium salts, which will be presented in the second part.
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Submitted on : Tuesday, December 11, 2007 - 2:00:37 PM
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Jean-Baptiste Bourg. Etude de Diradicaux hétérocycliques. Autre. Université Paul Sabatier - Toulouse III, 2007. Français. ⟨tel-00195735⟩

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