Les diradicaux sont des espèces réputées extrêmement instables. A titre d'exemple, le<br />cyclobutanediyle qui est l'archétype de ce genre d'espèce en série carbonée n'a en effet pu<br />être isolé que dans des matrices à basse température.<br />La première partie de cet exposé sera consacrée aux diradicaux formés des éléments<br />lourds des groupes principaux.<br />Nous montrerons dans une introduction bibliographique comment l'utilisation de ces<br />hétéroéléments a permis l'isolation du premier diradical localisé singulet stable basé sur un<br />squelette formé uniquement des hétéroéléments bore et phosphore.<br />Dans un deuxième chapitre, nous nous intéresserons aux isomères de ce diradical, en<br />particulier ses isomères de valence. Après un bref retour sur le concept, nous étudierons les<br />facteurs qui permettent de stabiliser les différents isomères déjà connus. Nous montrerons<br />ensuite comment il a été possible d'isoler de nouveaux isomères.<br />Dans un troisième chapitre, nous nous arrêterons sur deux isomères de valence<br />particuliers et étudierons l'isomérie d'élongation (bond-stretch isomerism). Dans notre cas,<br />deux isomères qui ne diffèrent que par la longueur d'une liaison sont en équilibre. Grâce à<br />des études de RMN à température variable, nous mettrons en évidence l'influence des<br />facteurs électroniques dans cet équilibre.<br />Ce travail nous a amenés à nous interroger sur la possibilité de préparer un diradical<br />purement organique formé uniquement d'éléments de la seconde ligne : carbone et azote.<br />Cette réflexion nous a conduits à mettre au point une nouvelle méthode de synthèse de sels<br />d'iminium et d'imidazolinium que nous présenterons dans une deuxième partie.

Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Makina Eğitimi Anabilim Dalı, 2008. / Kaynakça var.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

The purpose of this thesis is to examine the abundance systematics of Li, Be and B, and Li isotopic systematics in lavas from the Society Islands, an enriched mantle (EMII) intraplate site, to further characterize the chemical signatures in the sources for ocean island basalts that may result from subduction-related processes and mantle entrainment. The goal is to see how light-element and Li-isotope systematics vary during ocean-island volcanic evolution and during tropical weathering.B/K, B/Be and Li/V ratios in basaltic Moorea lavas are 0.0001-.0002, 0.6-2.0 and 0.01-0.05 respectively, and the more evolved samples are somewhat higher. These ratios are similar to those for other Society Island lavas, and lower than those for lavas from St. Helena, Erebus, Hawaii, Gough and Reunion, as well as analyzed mid-ocean ridge basalts (MORBs). Li values for Moorea cluster at +3 +5 percent for the freshest lavas, and 0+2 percent for more weathered rocks.These new data from Moorea are consistent with earlier survey results from the Society Islands and indicate a mantle source that includes B-poor (subducted) materials. 7Li values for the freshest Moorea samples are similar to those of other Society Island lavas, suggesting that the EMII isotopic end-member records a Li-isotopic signature similar to that of MORBs. Dilution by entrainment of upper mantle material is unlikely due to differing B/K ratios and similar Li values for the Society and Hawaiian plumes.

Boron arsenide is a compound main group semiconductor with a theoretical band gap in the range of 1.1 to 1.6 eV. Despite this ideal band gap, experimental studies of boron arsenide are very limited. In the present work, single source precursors with covalent bonds between boron and arsenic and labile ligands have been designed and synthesized. These precursors underwent thermal or chemical treatment to produce boron arsenide materials. Boron arsenide has also been prepared as a thin layer deposited on a boron substrate and a p-type photoelectrode was prepared from this material. The structure of the product was identified on the basis of X-ray diffraction and scanning electron microscopy, and the surface composition was determined by means of X-ray photoelectron spectroscopy. The electrode was found to be photoactive under both visible and UV-visible light irradiation and displayed a photocurrent of approximately 0.1 mA/cm² under UV-visible light irradiation at an applied potential of -0.25 V vs. Ag/AgCl. The valence band was estimated to be -5.1 eV. The indirect band gap, as determined from incident photo-to-electron conversion efficiency plots, is 1.46 eV. An ester-fuctionalized salophen aluminum complex that features a polymerizable bithiophene as the ester R group has been designed and synthesized. Metallopolymers of this type offer the additional advantages of processability and uniformity of the resulting films. The new salophen complex exhibited emission in the blue region at 491 nm with a quantum yield of 8.19%, which is significantly larger than that of the isolated ligand. Electropolymerization of this complex on a platinum button electrode resulted in the formation of an electrically conductive polymer that is also ionically conductive at low scan rates. In the polymeric form, the emission wavelength was found to be red-shifted to 505 nm. / text

(-)-Kainic acid and its C-4 epimer, (+)-allokainic acid are parent members of a class of substituted pyrrolidines known as kainoids. They have been found to exhibit powerful biological properties, principally neuroexcitatory. Kainic acid has become especially important in the study of Alzheimer's disease, epilepsy, and other neurological disorders. The total syntheses of (-)-kainic acid and (+)-allokainic acid were achieved using (L)-glutamic acid as the starting material and the sole source of stereochemical induction. The key steps for these successful syntheses involve formation of the gamma-lactam core via rhodium (II) catalyzed intramolecular C-H insertion of the alpha-diazo-alpha-(phenylsulfonyl)acetamide intermediate and the stereoselective dephenylsufonylation. Pd(II)-catalyzed and oxygen promoted carbon-carbon bond formation methodologies using organoboronic reagents were developed. The first one is a mild and efficient Pd(II) catalysis, leading to the formation of carbon-carbon bonds between a broad spectrum of organoboron compounds and alkenes. Molecular oxygen was employed to reoxidize the resultant Pd(0) species back to Pd(II) during catalytic cycles.This oxygen protocol promoted the desired Pd(II) catalysis, whereas it retarded competing Pd(0) catalytic pathways such as Heck or Suzuki couplings. The second one is the formation of symmetric biaryls and dienes via oxidative dimerization of aryl and alkenyl boronic acids. These conditions utilized Pd(II) catalysts under an oxygen atmosphere with water as the solvent. The use of phase transfer catalysts promoted efficient and mild syntheses of a wide range of materials.

Not available / text

The boron isotopic ratios of three contaminated ground water samples and of leachate from four fly ash samples are shown to be significantly different than the isotopic ratio of naturally occurring boron in a selected ground water. Analysis is performed using thermal ionization mass spectrometry with a precision of less than 1 per mil. Inductively coupled plasma mass spectrometry is shown to be ineffective for this application. Boron is isolated from solution and concentrated using Amberlite IRA-743 resin with no isotopic fractionation observed. Boron desorption from fly ash is shown to be rapid. Boron isotopic analysis is shown to be a superior method to boron concentration analysis for identifying leachate in a ground water, (1) at the outer limits of a leachate plume, and, (2) when the difference between the boron concentration of the leachate and background water is small. The degree of contamination can be determined if both end members are known.

Not available / text