21 resultados para Nucleophilic additions


Relevância:

10.00% 10.00%

Publicador:

Resumo:

Stocks added to (deleted from) the Russell 2000 and the S&P 600 indexes experience positive (negative) abnormal returns following the announcement. However, researchers disagree on whether these abnormal returns are permanent or temporary and offer competing explanations. I address this controversy by examining market reactions for firms that are added to or deleted from the FTSE Small Cap index (the main testing sample) and the S&P/TSX SmallCap index (the comparison sample). For the main testing sample, all stocks except pure additions, experience a permanent price change that is accompanied by a permanent change in liquidity. However, for the comparison sample, abnormal returns over the announcement period fully reverted within 30 days. In further examination of stock liquidity for the main testing sample, sample stocks experience permanent change in liquidity. Taken together, the observed results support the price pressure and liquidity hypotheses.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

This thesis explored the development of several methodologies for the stereoselective construction of ligand frameworks and some of their applications. The first segment concerns the application of an enantioselective lithiation at an Sp3_ hybridized position adjacent to nitrogen by means of the widely used and typically highly effective enantioselective lithiation with ( -)-sparteine. This investigation was intended to develop a method to install chirality into a system that would be converted into a family of diaminoylidenes for use as phosphine mimics in transition metal catalysis or as nucleophilic reagents. Molecular modeling of the system revealed some key interactions between the substrate and (-)-sparteine that provided general insight into the diamine's mode of action and should lend some predictive value to its future applications. The second portion focuses on the development of methods to access 1,2- disubstituted aminoferrocenes, an underexplored class of metallocenes possessing planar chirality. Two routes were examined involving a diastereoselective and an enantioselective pathway, where the latter method made use of the first BF3-mediated lithiation-substitution to install planar chirality. Key derivatives such as 1,2- aminophosphines, made readily accessible by the new route, were evaluated as ligands for Pd(II), Pt(II) and Ir(I). These complexes show activity in a number of transformations with both achiral and prochiral substrates. Optimization experiments were conducted to prepare enantiomerically enriched 2-substituted-I-aminoferrocenes by direct asymmetric lithiation of BF3-coordinated tertiary aminoferrocenes. A predictive computational model describing the transition state of this reaction was developed in collaboration with Professor Travis Dudding's group (Department of Chemistry, Brock University). The predicted stereochemistry of the process was confirmed by single-crystal X-ray analysis of a 2-phosphino-l-dimethylaminoferrocene derivative. Enantiomerically pure samples of the aminophosphine ligands derived from this new process have given promising preliminary results in the enantioselective hydrogenation of prochiral alkenes and warrant further stUdy in metal-mediated catalysis.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The origins of the Welland County Fair date back to the founding of the County of Welland in 1852. A provincial charter was issued in 1853 to create the Welland County Agricultural Society that was to operate the Fair. In 1970, the Welland County Fair became the Niagara Regional Exhibition, and the Society became known as the Niagara Regional Agriculture Society. The Society seeks to “encourage interest, promote improvements in and advance the standards of agriculture, domestic industry and rural life”. The Welland Festival of Arts was developed in 1986 in order to revitalize the town’s economy. An “outdoor art gallery” was created by painting murals on buildings that depicted the town’s heritage, a concept successfully adopted by the town of Chemainus, B.C. The first mural was completed in the summer of 1988, and by 1991 there were a total of 28 murals around the city. The endeavour proved successful: in the years that followed the creation of the Festival, two new hotels were constructed, a third was expanded, and there was an addition to the Seaway Mall to accommodate the increased tourist traffic. Optimist International is a non-profit organization that strives to “bring out the best in kids” . The first Canadian club was formed in Toronto in 1924. The Welland branch of the Optimist Club was founded in 1937. The first Welland County General Hospital opened in 1908. As the population increased, it became necessary to expand the existing facilities. Additions were made to the original structure with an East wing in 1930 and a children’s ward in 1931. However, in the 1950’s, the hospital was operating beyond optimum capacity and the need for a larger facility was clear. It was decided that a new hospital would be built, which opened in April 1960. The new hospital had 259 beds and 51 bassinets. Further additions were made in 1967 and 1978. The County of Welland was formed in 1850 when it was officially separated from Lincoln County, however, the two counties continued to operate together until 1856 when a new County building and jail for Welland County were completed. That same year, the first meeting of the Council of the Corporation of Welland County took place. The final meeting of the Council took place on December 18, 1969. The following year, the County of Welland merged with Lincoln County to form the Regional Municipality of Niagara. The Welland Mills in Thorold, Ont., was built in 1846-1847 by Jacob Keefer and is thought to have been one of the largest flour mills in Upper Canada. Ownership of the mill changed several times over the years and previous owners include the Howland family, the Hedley Shaw Milling Company and the Maple Leaf Milling Company. In 1986, the building received a heritage plaque from the Ontario Heritage Foundation, an agency of the Ontario Ministry of Culture and Recreation. At this time, the mill was no longer in operation and was being used for storage by Fraser, Inc. By 2006, the dilapidated building had been redeveloped into18 apartments and 2 floors of commercial space, while maintaining many heritage features. The building is currently known as the Welland Mills Centre.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

We examine stock market reactions around the Nasdaq-100 Index reconstitutions. We find a symmetric and transitory price response accompanied by a significant increase in trading volume on the effective date. Firms added to the Nasdaq-100 Index experience significant increases in institutional ownership, the number of market makers, and the number of shareholders. In contrast, firms removed from the index show significant decreases in the number of institutional shareholders. Additions to the Nasdaq-100 Index also show significant increases in four liquidity measures, whereas deletions demonstrate significant decreases in two liquidity measures. These changes in liquidity are related to the abnormal return on the announcement day. Taken together, the results suggest support for the price pressure, liquidity, and investor awareness hypotheses.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The preparation and characterization of two families of building blocks for molecule-based magnetic and conducting materials are described in three projects. In the first project the synthesis and characterization of three bis-imine ligands LI - L3 is reported. Coordination of LI to a series of metal salts afforded the five novel coordination complexes Sn(L4)C4 (I), [Mn(L4)(u-CI)(CI)(EtOH)h (II), [CU(L4)(u-sal) h(CI04)2 (sal = salicylaldehyde anion) (III), [Fe(Ls)2]CI (IV) and [Fe(LI)h(u-O) (V). All complexes have been structurally and magnetically characterized. X-ray diffraction studies revealed that, upon coordination to Lewis acidic metal salts, the imine bonds of LI are susceptible to nucleophilic attack. As a consequence, the coordination complexes (I) - (IV) contain either the cyclised ligand L4 or hydrolysed ligand Ls. In contrast, the dimeric Fe3+ complex (V) comprises two intact ligand LI molecules. In. this complex, the ligand chelates two Fe(III) centres in a bis-bidentate manner through the lone pairs of a phenoxy oxygen and an imine nitrogen atom. Magnetic studies of complexes (II-V) indicate that the dominant interactions between neighbouring metal centres in all of the complexes are antiferromagnetic. In the second project the synthesis and characterization two families of TTF donors, namely the cyano aryl compounds (VI) - (XI) and the his-aryl TTF derivatives (XII) - (XIV) are reported. The crystal structures of compounds (VI), (VII), (IX) and (XII) exhibit regular stacks comprising of neutral donors. The UV -Vis spectra of compounds (VI) - (XIV) present an leT band, indicative of the transfer of electron density from the TTF donors to the aryl acceptor molecules. Chemical oxidation of donors (VI), (VII), (IX) and (XII) with iodine afforded a series of CT salts that where possible have been characterized by single crystal X -ray diffraction. Structural studies showed that the radical cations in these salts are organized in stacks comprising of dimers of oxidized TTF donors. All four salts behave as semiconductors, displaying room temperature conductivities ranging from 1.852 x 10-7 to 9.620 X 10-3 Scm-I. A second series of CT salts were successfully prepared via the technique of electrocrystallization. Following this methodology, single crystals of two CT salts were obtained. The single crystal X-ray structures of both salts are isostructural, displaying stacks formed by trimers of oxidized donors. Variable temperature conductivity measurements carried out on this series of CT salts reveal they also are semiconductors with conductivities ranging from 2.94 x 10-7 to 1.960 X 10-3 S em-I at room temperature. In the third project the synthesis and characterization of a series of MII(hfac)2 coordination complexes of donor ligand (XII) where M2+ = Co2+, Cu2+, Ni2+ and Zn2+ are reported. These complexes crystallize in a head-to-tail arrangement of TTF donor and bipyridine moieties, placing the metal centres and hfac ligands are located outside the stacks. Magnetic studies of the complexes (XV) - (XVIII) indicate that the bulky hfac ligands prevent neighbouring metal centres from assembling in close proximity, and thus they are magnetically isolated.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The origins of the St. Catharines Collegiate Institute can be traced back to the formation of the Grantham Academy on Church St. in 1829. In 1845, the name was changed to the St. Catharines District Grammar School and in 1890 the Grammar School was renamed the St. Catharines Collegiate Institute. The current site of the school on Catherine Street was built in 1923 to accommodate the increasing demand for technical education, and became known as the St. Catharines Collegiate Institute and Vocational School. The school was enlarged with additions in 1945, 1965 and 1969. In 2006, the school underwent major renovations, which were completed in 2008. It is currently a secondary school administered by the District School Board of Niagara.