No description available.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1974. / Includes bibliographical references (leaves 81-84).

Thesis (Ph.D.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2006. / Härtill 4 uppsatser.

Thesis (M.Sc. Chemistry)--University of Waikato, 2008. / Title from PDF cover (viewed September 18, 2008) Includes bibliographical references (p. 70-80)

No description available.

Density functional theory calculations have been used to investigate catalytic mechanism of polymer formation containing polar groups, from the synthesis of the monomer to the synthesis of the macromolecule. In the spirit of a sustainable and green chemistry, we initially focused attention on the coupling of CO2 as economically convenient and recyclable C1 source with C2H4 to form acrylate and/or butirro-lactone, two important polar monomers. In this process formation of a mettallolactone via oxidative coupling of CO2 and C2H4 is an important intermediate. Given this background, we explored in detail (chapter-3) several Ni based catalysts for CO2 coupling with C2H4 to form acrylate. In this thesis we report on the competitive reaction mechanisms (inner vs outer sphere) for the oxidative coupling of CO2 and ethylene for a set of 11 Ni-based complexes containing bisphosphine ligands. In another effort, considering incorporation of a C=C bond into a metal-oxygen-Functional-Group moiety is a challenging step in several polymerization reactions, we explored the details of this reaction (chapter4) using two different catalysts that are capable to perform this reaction in the synthesis of heterocycles. Specifically, the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-Bis-diphenylphosphino-propane), and the [Pd]/BPh3 intramolecular alkoxyfunctionalizations. Rest of the thesis we worked on understanding the details of the polymerization of polar monomers using organocatalysts based on N-heterocyclic carbenes (NHC) or N-heterocyclic olefins (NHO). In particular (chapter-5) we studied the polymerization of N-methyl N-carboxy- anhydrides, towards cyclic poly(N-substituted glycine)s, promoted by NHC catalysts. In good agreement with the experimental findings, we demonstrated that NHC promoted ring opening polymerization of N-Me N-Carboxyanhydrides may proceed via two different catalytic pathways. In a similar effort we studied polymerization of propylene oxide (PO) (chapter-6) promoted by N-heterocyclic olefins (NHO) in combination with benzylic alcohol (BnOH). Calculations support the experimental observation that there might be two different catalytic pathways namely the anionic and the zwitterionic pathways. Potential energy surfaces analysis suggested in different NHO one or other mechanism is operational which is strongly depends on steric and electronic properties of particular NHO taken in account.

Les travaux décrits dans ce manuscrit de thèse concernent l’exploitation des interactions acide-base de Lewis entre deux partenaires organophosphorés et organoborés. Quatre types d’interactions ont été particulièrement au cœur de notre étude, allant de la frustration de la liaison P-B à la formation de complexes acide base de Lewis fortement liés. L’étude de ces interactions, couplée à des outils de physico-chimie organique et de chimie théorique, nous ont permis, non seulement de comprendre les paramètres clés de la réactivité mais également de mettre en avant de nouvelles voies de synthèse. Dans un premier temps, notre étude s’est portée sur l’hydrogénation de composés insaturés par les Paires de Lewis Frustrées (FLP). Ainsi, l’origine de l’incapacité des P/B à réduire les accepteurs de Michael a été expliquée par des mesures cinétiques de la nucléophilie et de la basicité de Lewis de phosphines encombrées. Dans une seconde partie, l’hydricité de complexes de phosphine borane (PBs) variées a été mesurée, nous permettant d’établir une échelle de prédiction de la réduction de divers électrophiles en présence de ces donneurs d’hydrure ioniques. Cette étude nous a conduit à considérer les PBs comme substrats dans des réaction de borylation intramoléculaire impliquant BH3 comme source de bore. Cependant, des résultats inattendus ont mis en exergue une migration prépondérante à la borylation lors de la réaction entre les PBs et un acide de Lewis, donnant accès à une nouvelle familles de PBs possédant un atome de bore électro-déficitaire. Des études cinétiques couplées à une étude par DFT ont permis de rationaliser la réactivité observée. Enfin, l’exploitation des interactions réversibles entre une phosphine secondaire et un acide de Lewis organique ou métallique nous ont permis de contrôler la régiosélectivité lors de l’hydrophosphination d’alcènes 1,1-disubstitués par les diarylphosphines. Nos études mécanistiques soutiennent fortement l’implication d’un carbocation comme intermédiaire réactionnel. / The research in this thesis describes the exploration of the Lewis-acid Lewis-base interactions between organophopshine and organoborane compounds. We focused our attention on four types of interactions going from frustrating to stong P-B bonds. Our understanding of these interactions is based on detailed kinetics and computational calculations, allowing us to find a new reactivity of these species. In a first part, we studied the metal-free hydrogenation of unsaturated compounds using Frustrated Lewis Pairs (FLPs). Based on the measurement of the nucleophilicity and the Lewis basicity parameters of sterically hindered phosphines, we were able to explain reasons of the failure of P/B FLPs to catalyse the hydrogenation of Michael acceptors under H2. In the second chapter, we employed the Mayr’s linear-free energy relationship to measure the hydricity of various phosphine borane complexes (PBs) and compare their reactivity to commons hydride donors. Based on these kinetic parameters, we next turned our attention to investigate the effect of a strong Lewis acid, (B(C6F5)3), to prevent the expected intramolecular borylation of PBs to take place. By combining kinetic and computational investigations, we have been able to understand factors controlling this reaction. In the last chapter, we reported on the regioselective organocatalytic Markovnikov hydrophosphination of aryl alkenes. Importantly, we highlighted that the reversible formation of a phosphine-Lewis acid complex is in the core of the catalytic process. Mechanistic investigations support the formation of a carbocation in the catalytic cycle.

No description available.

The competition between substitution (SN2) and elimination (E2) in nucleophilic reactions of alkyl halides has had a profound influence on the development of physical organic chemistry and remains an important testing ground for identifying reactivity patterns in gas-phase organic chemistry. Here, the competition between substitution and elimination, as well as the regioselectivity of E2 reactions have been examined in the gas phase. By doing so, the intrinsic reactivity patterns can be probed in the absence of solvation effects. The SN2 and E2 reactions of a large set of alkyl bromides with varying substitution patterns at the α- and β-carbons were studied in the gas phase using naphthoate and phenoxide-based dianion nucleophiles. The experiments were performed in a quadrupole ion trap mass spectrometer equipped with electrospray ionization. The experimental work was supported by calculations at the MP2/6-31+G(d,p)//MP2/6-31+G(d) level. The naphthoate is a weaker base and leads to more products from the SN2 pathway. In accord with generalizations from condensed-phase results, primary bromides generally prefer substitution pathways and secondary bromides prefer eliminations. In the gas phase, polarizability is more important, and the highest SN2 reactivity is observed when the β-carbon is 2° - steric crowding from β-substituents is not as significant for un-solvated nucleophiles. In addition, the data confirms that alkyl substituents at the β-carbon have a greater accelerating effect on E2 reactions than those at the α-carbon. Finally, computed data based on lowest enthalpy pathways provide poor descriptions of the reactions of the larger alkyl bromides and are skewed toward crowded systems that offer stabilizing, nonbonded interactions at the expense of conformational freedom. An investigation of regiochemical preferences of E2 reactions was also explored by synthesizing and analyzing the product distributions of a set of deuterium-labeled compounds capable of Saytzeff and Hofmann elimination. Gas-phase reactions of these substrates with dianion nucleophiles indicate that as expected, there is a preference for the Saytzeff product, which is also preferred in solution. This is the first study of E2 regioselectivity in the gas phase for a simple alkyl system.