ERIC Number: EJ1133428
Record Type: Journal
Publication Date: 2017-Feb
Abstractor: As Provided
Reference Count: 11
Teaching Experiment to Elucidate a Cation-Pi Effect in an Alkyne Cycloaddition Reaction and Illustrate Hypothesis-Driven Design of Experiments
St.Germain, Elijah J.; Horowitz, Andrew S.; Rucco, Dominic; Rezler, Evonne M.; Lepore, Salvatore D.
Journal of Chemical Education, v94 n2 p240-243 Feb 2017
An organic chemistry experiment is described that is based on recent research to elucidate a novel cation-pi interaction between tetraalkammonium cations and propargyl hydrazines. This nonbonded interaction is a key component of the mechanism of ammonium-catalyzed intramolecular cycloaddition of nitrogen to the terminal carbon of a C-C triple bond of the propargyl substrate. In this teaching experiment, reactions and control experiments are employed to demonstrate the testing of two alternative mechanistic hypotheses. Specifically, cyclization reactions are performed with a soluble base (sodium phenoxide) with and without tetrabutylammonium bromide under homogeneous conditions. Students observe that the added ammonium salt accelerates the reaction. They are then encouraged to develop a testable hypothesis for the role of the ammonium salt in the cyclization mechanism: typical phase transfer or other. IR spectroscopy is then used to directly observe a dose dependent shift of the alkyne stretching mode due to a cation-pi interaction. In this experiment, undergraduate "researchers" were able to practice the scientific method on a contemporary system and see how data are generated and interpreted to adjudicate between rival hypotheses in a way that emulates authentic and current research in a lab setting. This experimental design was tested on students enrolled in the introductory undergraduate organic chemistry lab.
Descriptors: Organic Chemistry, Science Experiments, College Science, Undergraduate Study, Inquiry, Spectroscopy, Science Laboratories, Laboratory Experiments, Hypothesis Testing, Molecular Structure
Division of Chemical Education, Inc and ACS Publications Division of the American Chemical Society. 1155 Sixteenth Street NW, Washington, DC 20036. Tel: 800-227-5558; Tel: 202-872-4600; e-mail: firstname.lastname@example.org; Web site: http://pubs.acs.org/jchemeduc
Publication Type: Journal Articles; Reports - Descriptive
Education Level: Higher Education; Postsecondary Education
Sponsor: National Institutes of Health (DHHS)
Authoring Institution: N/A
Grant or Contract Numbers: GM110651