Analysis of Bromination of Ethylbenzene Using a 45 MHz NMR Spectrometer: An Undergraduate Organic Chemistry Laboratory Experiment

A 45 MHz benchtop NMR spectrometer is used to identify the structures and determine the amount of 1-bromoethylbenzene and 1,1-dibromoethylbenzene produced from free-radical bromination of ethylbenzene. The experiment is designed for nonchemistry majors, specifically B.S. Biology students, in a predominantly undergraduate institution with insufficient resources for the initial cost and maintenance of high-field Fourier transform (FT) NMR instrumentation. Students learn the basic concepts of nuclear magnetic resonance, acquire FID (free-induction decay) signals, process the data, interpret, assign peaks, and determine product composition. The experiment demonstrates to students that NMR spectroscopy can be used for molecular structure characterization and for determination of product yields. Hands-on experience with a low-field spectrometer provides undergraduate students with confidence to run an NMR instrument while minimizing fear that can be generated at the sight of high field FT-NMR instrumentation.