Browsing by Subject "Rearrangements (Chemistry)"
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Item A study of the mechanism of the thermal rearrangement of 2.2'-Hydrazonaphthalene(Texas Tech University, 1959-08) Trisler, John CharlesNot availableItem Heavy-atom kinetic isotope effects and mechanism of the acid-catalyzed o-semidine and p-semidine rearrangements and disproportionation of 4,4'-dichlorohydrazobenzene(Texas Tech University, 1986-05) Rhee, Eun-sook JangNot availableItem Heavy-atom kinetic isotope effects in solving mechanisms of: benzidine rearrangements : hydrazobenzene and 2,2'-dimethoxyhydrazobenzene(Texas Tech University, 1983-12) Park, Koon HaNot availableItem Migration tendency of substituents in some cationic rearrangement reactions(Texas Tech University, 1982-05) Hong, Yen-long VincentNot availableItem Item Synthesis of alcohol substrate for [3,3]- and [3,5]-sigmatropic rearrangements and indenyl yttrium complexes as models for olefin polymerization catalysts(2012-05) Mehra, Rudhran; Birney, David M.; Bradley, Christopher A.Sigmatropic rearrangements are an important class of pericyclic reactions. These rearrangements can provide “clean” products as they can be easily carried out at relatively low temperatures and/or under photochemical conditions. Pericyclic reactions can be explained using several theories - Frontier Molecular Orbital (FMO) theory, Woodward- Hoffmann rules and Aromatic Transition State theory. In 1976, Lemal and co-workers coined the term “pseudopericyclic” for a class of rearrangements that were distinguished by the presence of “orbital disconnections”. Beginning nearly 20 years later, Birney and co-workers have further shed light on the nature of these rearrangements. The transition states observed in these reactions also differ from planar to almost planar which affects the degree of pseudopericyclic character. The exact nature of pseudopericyclic reactions, however, continues to be of interest to the scientific community. The first part of the thesis discusses the background and current work done on pseudopericyclic reactions. The second part of the manuscript discusses a series of [3,3]- and [3,5]-rearrangements that have been designed to further elucidate their pericyclic/pseudopericyclic character. These systems could have six- and eight- member transition structures via [3,3]- and [3,5]-sigmatropic rearrangements The synthesis involves making the acetate, trichloroacetimidate, dimethyl thiocarbamate, xanthate and vinyl ether of a substrate dienol. The synthesis of the dienol is also discussed. The third part of the thesis discusses the synthesis of a novel indenyl yttrium complexes used as a model for active catalyst in Group 3 olefin polymerizations. A number of ligands have been discussed and synthesized. Using these ligands as ancillary supports, we have synthesized an indenyl yttrium complex that mimics the active species in olefin polymerization. Specifically, attempts have been made to study the insertion of a Y-carbon bond into the indenyl benzo ring at different temperatures and the β-elimination step. One of the biggest potential drawbacks of the indenyl complexes is the deactivation of the catalyst via insertion into the ligands; which directly affects the chain length, stereochemistry and molecular weight of the polymer. This in turn can drastically impact the mechanical, chemical, and physical properties of the polymer.Item The acid-catalyzed reactions of some N, N'-dimethylhydrazoaromatics(Texas Tech University, 1976-05) Walzel, Gerald LNot availableItem The migration tendency of unsaturated substituents in a cationic rearrangement(Texas Tech University, 1984-12) Hahn, Young-sook PaikNot availableItem Unnatural amino acids: synthesis and structure-property relationship studies(Texas Tech University, 1998-08) Starnes, Stephen DwightThe conformations, tautomerization, and aggregation of different unnatural amino acids were examined in solution and in the gas phase. These properties were analyzed using H NMR spectroscopy, IR spectroscopy and computational chemistry techniques. H NMR spectroscopy was used to quantify the substituent effects on the tautomerization of substituted N,N-dimethylamino acids in DMSO. The results show that the tautomeric equilibrium constant is shifted to the unionized tautomer with increased branching on the p-carbon of the amino acid. The results are explained in terms of the substituent steric and solvation effects on the conformation of the amino acids. Additionally, variable temperature H NMR spectroscopy illustrated that N,Ndimethylphenylglycine derivatives associate in aqueous solution due to hydrophobic and intermolecular hydrogen bonding interactions. ab Initio calculations were utilized to examine the conformational potential energy surface (PES) of fiuorinated and N-alkyl substituted amino acids. For 2-fluoroglycine, 2,2-difluoroglycine, and 3,3,3-trifluoroalanine, the resuhs of the study show that for each amino acid conformation, the optimized geometry is highly dependent on the level of theory utilized. For instance, the amino group is planar at some, but not all, levels of theory. The anomeric effect and intramolecular hydrogen bonding interactions were shown to be important stabilizing factors of the gas phase conformations of these species. For N-alkyl substituted amino acids, the conformations of N-methylglycine and N,N-dimethylglycine have been examined and the results reveal the importance of hydrogen bonding interactions as a stabilizing element for each conformation. The tautomerization of N-methylglycine and N,N-dimethylglycine was also examined by ab initio methods and the results indicate that the "stretched out" conformation of N,N-dimethylglycine zwitterion is a minimum on the conformational PES in the gas phase. This is believed to be one of the first amino acid zwitterions predicted to be a real molecule in the gas phase. A viable pathway for the synthesis of conformationally constrained P,P-alkyl substituted cysteine analogs was examined. The pathway has been described in the chemical Hterature, however the route has not been optimized to readily give the desired cysteine derivatives. This study examined this route in more detail.