Use of 1H, 13C, and 19F-NMR Spectroscopy and Computational Modeling To Explore Chemoselectivity in the Formation of a Grignard Reagent

Research Article | Journal of Chemical Education
Use of ¹H, ¹³C, and ¹⁹F-NMR Spectroscopy and Computational Modeling To Explore Chemoselectivity in the Formation of a Grignard Reagent
Author's Information

Sara M. Hein

Department of Chemistry, Winona State University, Winona, Minnesota 55987, United States

Robert W. Kopitzke

Department of Chemistry, Winona State University, Winona, Minnesota 55987, United States

Thomas W. Nalli

Department of Chemistry, Winona State University, Winona, Minnesota 55987, United States

Brian J. Esselman

Department of Chemistry, University of Wisconsin?Madison, Madison, Wisconsin 53706, United States

Nicholas J. Hill

Department of Chemistry, University of Wisconsin?Madison, Madison, Wisconsin 53706, United States
Abstract

A discovery-based Grignard experiment for a second-year undergraduate organic chemistry course is described. The exclusive Grignard reagent formed by the reaction of 1-bromo-4-fluorobenzene (1) with Mg is 4-fluorophenylmagnesium bromide (2), which is treated with either benzophenone or CO₂ to produce the corresponding fluorinated alcohol (3) or benzoic acid (4), respectively. The use of a dihalogenated Grignard reagent requires students to discern its reactivity for synthesis. Students predict the chemoselectivity of Grignard reagent formation based on the C�X bond energies of 1 and investigate their predictions by analysis of ¹H, ¹³C, and ¹⁹F NMR, EI�MS, and IR data of 3 and 4. Empirical parameters and DFT calculations are used to predict the ¹H and ¹³C NMR chemical shifts of 4 and the hypothetical brominated analogue.

Keywords

Aldehydes/Ketones; Carboxylic Acids; Computational Chemistry; Grignard Reagents; Inquiry-Based/Discovery Learning; Laboratory Instruction; NMR Spectroscopy; Organic Chemistry; Second-Year Undergraduate

DOI: 10.1021/ed500700c

ADLID: 10187-v4

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Keywords
Aldehydes/Ketones Carboxylic Acids Computational Chemistry Grignard Reagents Inquiry-Based/Discovery Learning Laboratory Instruction NMR Spectroscopy Organic Chemistry Second-Year Undergraduate

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