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ERIC Number: ED533470
Record Type: Non-Journal
Publication Date: 2011
Pages: 256
Abstractor: As Provided
Reference Count: 0
ISBN: ISBN-978-1-1248-8225-3
I. the Synthesis and Coordination Chemistry of Novel 6Pi-Electron Ligands. II. Improvement of Student Writing Skills in General Chemistry Lab Reports through the Use of Calibrated Peer Review
William, Wilson Ngambeki
ProQuest LLC, Ph.D. Dissertation, The University of New Mexico
Abstract I. The goal of this study was to synthesize and characterize a set of coordination complexes containing 6pi-cationic ligands. These compounds could be extremely useful as catalysts for the polymerization of olefins that are widely used in the synthetic polymer industry. The original strategy was to synthesize the 6pi-cationic ligands using (Ph[subscript 2]P) [subscript 3]CH (1) and (Me[subscript 2]P)[subscript 3]CH (10) as precursors; however, both precursors 1 and 10 were found to be highly reactive leading to the fragmentation products (Ph [subscript 2]P)[subscript 2]CH[subscript 2] and (Me[subscript 2]P)[subscript 2]CH [subscript 2] respectively. In trying to control the reactivity, precursor 1 was coordinated to the group 6B metal carbonyl in two modes, Mo(CO)[subscript 3](C [subscript 2]H[subscript 5]CN)(Ph[subscript 2]P)2CHPPh[subscript 2] and W(CO) [subscript 3](C[subscript 2]H[subscript 5]CN)(Ph[subscript 2]P)[subscript 2]CHPPh [subscript 2]. In these novel compounds, two of the three phosphorus atoms are chelated to the metal. These complexes were isolated and characterized by X-ray analysis, elemental analysis, NMR and infrared spectroscopy. When these metal complexes were reacted with B(C[subscript 6]F[subscript 5])[subscript 3], the complexes were stabilized, and no molecular fragmentation was observed. Instead, a second mode of coordination was observed by [supercript 31]P{[supercript 1]H} NMR spectroscopy, where all three phosphorus atoms are bonded to the metal in a tridentate fashion, yielding the novel product EtCNB(C[subscript 6]F [subscript 5])[subscript 3], which was characterized by X-ray analysis. However, because there was no hydride abstraction from the tertiary carbon in either compound, further studies will be required to develop a strategy for hydride abstraction to produce a cationic ligand. Another strategy for the synthesis of 6pi-cationic ligands was to directly synthesize the halogenated version of the tertiary carbon atom of compound 10. Fractional recrystallization of the crude product yielded two compounds of 2,4,6-trimethypyridinium bromide and (PMe[subscript 2])[subscript 3]CBr. (PMe[subscript 2])[subscript 3]CBr was determined to be pure as revealed by [superscript 31]P{[superscript 1]H} NMR. It is expected that oxidation of the bromide should yield the 6pi-cationic ligand. In the next strategy, density function theory calculations (DFT) were used to predict the possibility that the 6pi-cationic ligand of guanidinium analog would coordinate with a group 6B metal carbonyl. However, attempts to synthesize the predicted complex were unsuccessful; when neodymium nitrate was reacted with the 6pi-cationic ligand of guanidinium salt, a completely novel diguanidinium diaquapentakis(nitrato)neodymiate(III) was produced, as characterized by X-ray analysis, NMR, elemental analysis, and infrared spectroscopy. In the next approach, the synthesis of the 6pi-cationic ligand of guanidinium analog tripiperidine carbenium tetrafluoroborate was attempted; again the ligand could not be obtained; however, other novel compounds, 1-tritylpiperidine and diphenyldipiperidin-1-ylmethane were obtained as indicated by single crystal X-ray analysis. The last strategy was to synthesize a 6pi-anionic phosphorus-based complex using 2,4,6-tri-"tert"-butylaniline and PI[subscript 5]. While the desired complex was not obtained, another novel compound, 2,4,6-tri- "tert"-butylbenzenaminium iodide, was produced and characterized by single crystal X-ray analysis and [superscript 1]H NMR. In conclusion, new strategies that combine DFT with novel synthetic approaches will be required to successfully produce coordination complexes containing 6pi-cationic ligands. Abstract II. The goal of this study was to assess effectiveness of using Calibrated Peer Review (CPR) for submitting post-lab reports. According to the literature the use of CPR could help improve students' writing skills (WS), conceptual understanding (CU) and critical thinking (CT). The first strategy of this study was to divide all students into two groups and required one group to use CPR for writing post-lab reports. The performances of the post-lab between the two groups were then compared. In second strategy I used an essay (pretest/posttest) to objectively assess students' writing skills that showed an improvement of 19% from students' who used CPR and 11% from students' who did not use CPR. When we compared the percentage of students who were not proficient in any areas (WS, CU, or CT) between the pre- and post-test, the CPR group has more improvement (22%) over the non-CPR group, which is 17%. Statistical analyses (t-test and ANOVA) for pretest and posttest scores have also shown significant differences in means and variances for CPR and non CPR students. In the third strategy we collected feedback from students through survey questions regarding the usefulness of CPR from their point of view. We have obtained low rating (2 on a five point Likert scale) about the use of CPR for writing post-lab report from students. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page:]
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Publication Type: Dissertations/Theses - Doctoral Dissertations
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A