377 research outputs found
DFT-Assisted Design and Evaluation of Bifunctional Amine/Pyridine-Oxazoline Metal Catalysts for Additions of Ketones to Unactivated Alkenes and Alkynes
Bifunctional catalyst systems for the direct addition of Âketones to unactivated alkenes/alkynes were designed and modeled by density functional theory (DFT). The designed catalysts possess bidentate ligands suitable for binding of pi-acidic group 10 metals capable of activating alkenes/alkynes, and a tethered organocatalyst amine to Âactivate the ketone via formation of a nucleophilic enamine intermediate. The structures of the designed catalysts before and after C–C bond formation were optimized using DFT, and reaction steps involving group 10 metals were predicted to be significantly exergonic. A novel oxazoline precatalyst with a tethered amine separated by a meta-substituted benzene spacer was synthesized via a 10-step sequence that Âincludes a key regioselective epoxide ring-opening step. It was combined with group 10 metal salts, including cationic Pd(II) and Pt(II), and screened for the direct addition of ketones to several alkenes and an Âinternal alkyne. 1H NMR studies suggest that catalyst-catalyst interÂactions with this system via amine–metal coordination may preclude the desired addition reactions. The catalyst design approach disclosed here, and the promising calculations obtained with square planar group 10 metals, light a path for the discovery of novel bifunctional catalysts for C–C bond formation
Design and Synthesis of Oxazoline-Based Scaffolds for Hybrid Lewis Acid/Lewis Base Catalysis of Carbon–Carbon Bond Formation
A new class of hybrid Lewis acid/Lewis base catalysts has been designed and prepared with an initial objective of promoting stereoselective direct aldol reactions. Several scaffolds were synthesized that contain amine moieties capable of enamine catalysis, connected to heterocyclic metal-chelating sections composed of an oxazole–oxazoline or thiazole–oxazoline. Early screening results have identified oxaÂzole–oxazoline-based systems capable of promoting a highly diastereo- and enantioselective direct aldol reaction of propionaldehyde with 4-nitrobenzaldehyde, when combined with Lewis acids such as zinc triflate
Multifunctional Heterocyclic Scaffolds for Hybrid Lewis Acid/Lewis Base Catalysis of Carbon–Carbon Bond Formation
A controlled study of virtual reality in first-year magnetostatics
Stereoscopic virtual reality (VR) has experienced a resurgence due to
flagship products such as the Oculus Rift, HTC Vive and smartphone-based VR
solutions like Google Cardboard. This is causing the question to resurface: how
can stereoscopic VR be useful in instruction, if at all, and what are the
pedagogical best practices for its use? To address this, and to continue our
work in this sphere, we performed a study of 289 introductory physics students
who were sorted into three different treatment types: stereoscopic virtual
reality, WebGL simulation, and static 2D images, each designed to provide
information about magnetic fields and forces. Students were assessed using
preliminary items designed to focus on heavily-3D systems. We report on
assessment reliability, and on student performance. Overall, we find that
students who used VR did not significantly outperform students using other
treatment types. There were significant differences between sexes, as other
studies have noted. Dependence on students' self-reported 3D videogame play was
observed, in keeping with previous studies, but this dependence was not
restricted to the VR treatment.Comment: 6 pages, 4 figures, submitted to the 2019 Physics Education Research
Conferenc
DFT-assisted Design and Evaluation of Bifunctional Copper(I) Catalysts for the Direct Intermolecular Addition of Aldehydes and Ketones to Alkynes
Bifunctional catalysts containing discrete metal pi-acid and amine sites were designed and investigated for the direct intermolecular addition of aldehydes and ketones to unactivated alkynes. Copper(I)-based catalysts were prioritized based on intramolecular (Conia-ene type) reactions, and complexes were designed with tridentate ligands and potentially hemilabile heterocyclic spacers. The structures of the designed catalysts were computed using density functional theory (DFT), and the relative energies of putative catalytic intermediates were estimated and used to prioritize catalyst designs. Novel bifunctional precatalysts containing a thiazole spacer were synthesized via a 9-step sequence and combined with transition metals before screening for the direct addition of aldehydes and ketones to several internal and terminal alkynes. Despite the lack of desired intermolecular reactions, DFT calculations of putative catalyst intermediates appears to be a promising strategy for the design and prioritization of bifunctional catalysts for CC bond formation
Chest- and Waist-Deep Aquatic Plyometric Training and Average Force, Power, and Vertical-Jump Performance
Purpose: The purpose of the study was to compare effects of chest- and waist-deep water aquatic plyometrics on average force, power and vertical jump. Methods: Twenty-nine male and female participants were assigned to either a control group or 1 of 2 aquatic groups (waist deep and chest deep) and participated in a 6-wk, twice per wk plyometric training program. Average force and power were measured on a force plate using 3 jumps: squat, countermovement, and drop jump. Vertical-jump heights were also recorded. A repeated-measures ANOVA was used to determine significant differences between testing and groups on average force, power and vertical jump. Results: No significant differences were found with average force and power with the squat, countermovement, and vertical jumps. There were significant changes in drop jump average in the control group from the pretest to posttest. Conclusions: With the water depths chosen and held constant, there appears to be no increased benefit in performance variables
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