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ERIC Number: EJ1062181
Record Type: Journal
Publication Date: 2015-Mar
Pages: 5
Abstractor: As Provided
Reference Count: 11
ISBN: N/A
ISSN: ISSN-0021-9584
Using NMR Spectroscopy to Probe the Chemo- and Diastereoselectivity in the NaBH[subscript 4] Reduction of Benzoin Acetate and Benzoin Benzoate
Saba, Shahrokh; Cagino, Kristen; Bennett, Caitlin
Journal of Chemical Education, v92 n3 p543-547 Mar 2015
A pedagogically useful discovery-based undergraduate organic chemistry lab experiment probing the chemo- and diastereoselectivity in the NaBH[subscript 4] reduction of two chiral ketoesters (benzoin acetate and benzoin benzoate) has been developed. This experiment complements a previously described and highly popular discovery-based experiment that probes the stereoselectivity in the NaBH[subscript 4] reduction of the chiral ketone (±)-benzoin. Using reactions described in standard textbooks, students convert (±)-benzoin to the ketoester derivatives (±)-benzoin acetate and (±)-benzoin benzoate. In contrast to benzoin that has a single reducible ketone functional group, the ketoester derivatives have two reducible functional groups. In addition, the structural modifications made to the hydroxyl group of the benzoin molecule lead to an increase in the effective steric bulk of the OH group of benzoin, affording a larger acetoxy group and an even larger benzoxy group. Using NMR spectroscopy, students probe not only the chemoselectivity but also the diastereoselectivity associated with the NaBH[subscript 4] reduction of their difunctional substrates. In contrast to the NaBH[subscript 4] reduction of benzoin, which is highly diastereoselective (de ~ 100%) and affords ("R,S")-hydrobenzoin with near exclusion of its ("R,R")- and ("S,S")- counterparts, students discover a decreasing trend in diastereoselectivity going from benzoin to benzoin acetate and benzoin benzoate. These findings are then assessed with the help of qualitative predictions made by the Felkin-Anh model for nucleophilic addition to the carbonyl group.
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: eic@jce.acs.org; Web site: http://pubs.acs.org/jchemeduc
Publication Type: Journal Articles; Reports - Descriptive
Education Level: Higher Education; Postsecondary Education
Audience: N/A
Language: English
Sponsor: National Science Foundation
Authoring Institution: N/A
IES Grant or Contract Numbers: DUE 9650684