4 resultados para 2,4,6,8-tetraoxaadamantanes
em Brock University, Canada
Resumo:
This study sought to explore the current state of Grades 4 to 8 science education in Ontario from the perspective of Junior/Intermediate (J/I) teachers. The study’s methodology was a sequential 2-phased mixed methods explanatory design denoted as QUAN (qual) qual. Data were collected from an online survey and follow-up interviews. J/I teachers (N = 219) from 48 school boards in Ontario completed a survey that collected both quantitative and qualitative data. Interviewees were selected from the survey participant population (n = 6) to represent a range of teaching strategies, attitudes toward teaching science, and years of experience. Survey and interview questions inquired about teacher attitudes toward teaching science, academic and professional experiences, teaching strategies, support resources, and instructional time allotments. Quantitative data analyses involved the descriptive statistics and chi-square tests. Qualitative data was coded inductively and deductively. Academic background in science was found to significantly influence teachers’ reported level of capability to teach science. The undergraduate degrees held by J/I science teachers were found to significantly influence their reported levels of capability to teach science. Participants identified a lack of time allocated for science instruction and inadequate equipment and facilities as major limitations on science instruction. Science in schools was reported to be of a “second-tiered” value to language and mathematics. Implications of this study include improving undergraduate and preservice experiences of elementary teachers by supporting their science content knowledge and pedagogical content knowledge.
Resumo:
The effects of sample solvent composition and the injection volume, on the chromatographic peak profiles of two carbamate derivatives, methyl 2-benzimidazolecarbamate (MBC) and 3-butyl-2,4-dioxo[1,2-a]-s-triazinobenzimidazole (STB), were studied using reverse phase high performance liquid chromatograph. The study examined the effects of acetonitrile percentage in the sample solvent from 5 to 50%, effects of methanol percentage from 5 to 50%, effects of pH increase from 4.42 to 9.10, and effect of increasing buffer concentration from ° to 0.12M. The effects were studied at constant and increasing injection mass and at four injection volumes of 10, 50, 100 and 200 uL. The study demonstrated that the amount and the type of the organic solvents, the pH, and the buffer strength of the sample solution can have a pronounced effect on the peak heights, peak widths, and retention times of compounds analysed. MBC, which is capable of intramolecular hydrogen bonding and has no tendency to ionize, showed a predictable increase .in band broadening and a decrease in retention times at higher eluting strengths of the sample solvent. STB, which has a tendency to ionize or to strongly interact with the sample solvent, was influenced in various ways by the changes in ths sample solvent composition. The sample solvent effects became more pronounced as the injection volume increased and as the percentage of organic solvent in the sample solution became greater. The peak height increases for STB at increasing buffer concentrations became much more pronounced at higher analyte concentrations. It was shown that the widely accepted procedure of dissolving samples in the mobile phase does not yield the most efficient chromatograms. For that reason samples should be dissolved in the solutions with higher aqueous content than that of the mobile phase whenever possible. The results strongly recommend that all the samples and standards, regardless whether the standards are external or internal, be analysed at a constant sample composition and a constant injection volume.
Resumo:
New and robust methodologies have been designed for palladiumcatalyzed cross-coupling reactions involving a library of novel tertiary phosphine ligands incorporating a phospha-adamantane framework. The secondary phosphine, l,3,5,7-tetramethyl-2,4,8-trioxa-6-phospha-adamantane was converted into a small library of tertiary phosphine derivatives and the ability of these tertiary phosphaadamantanes to act as effective ligands in the palladium-catalyzed amination reaction and p-alkyl-Suzuki cross-coupling was examined. l,3,5,7-Tetramethyl-6- phenyl-2,4,8-trioxa-6-phosphaadamantane (PA-Ph) used in combination with Pd2(dba)3 CHCI3 facilitated the reaction of an array of aryl iodides, bromides and chlorides with a variety secondary and primary amines to give tertiary and secondary amines respectively in good to excellent yields. 8-(2,4-Dimethoxyphenyl)- l,3,5,7-tetramethyl-2,4,6-trioxa-8-phospha-tricyclo[3.3.1.1*3,7*]decane used in combination with Pd(0Ac)2 permitted the reaction of an array of alkyl iodides, and bromides with a variety aryl boronic acids and alkyl 9-BBN compounds in good to excellent yields. Subsequent to this work, the use of phosphorous based ionic liquids, specifically tetradecyltrihexylphosphonium chloride (THPC), in the Heck reaction provided good to excellent yields in the coupling of aryl iodides and bromides with a variety of olefins.
Resumo:
Survey map of the Second Welland Canal created by the Welland Canal Company showing the canal in Thorold South. Identified structures associated with the Canal include the Little Deep Cut and the towing path. The surveyors' measurements and notes can be seen in red and black ink and pencil. Local area landmarks are also identified and include streets and roads (ex. Road to Beaverdams and Road to Allanburgh), two unnamed bridges, the Spoil Bank, a pond, and the Back Water. Properties and property owners of note are: Lots 29 and 30, Jacob Keefer, John Brown, William Bouck, C. Gisso, and a property reserved for Bridge Tender.