Expanding the Scope of an Electrophilic Aromatic Substitution Discovery Experiment Including Hydride and Methyl Shifts

Abstract

Friedel–Crafts alkylation reactions using a curated set of alcohols provide students with the opportunity to combine the study of electrophilic aromatic substitution with carbocation rearrangements. In this experiment students may be presented with up to nine alcohols that yield six products, all synthesized under identical reaction conditions. They distinguish their products using a range of instrumental methods including infrared, 1H NMR, and 13C NMR spectroscopies, and mass spectrometry. Additional characterization is provided by the determination of melting point/mixed-melting point and gas chromatographic retention time. Students work in teams to assign structures to their individual reaction products; providing nine starting materials ensures minimal duplicates in a given laboratory section. As students interpret their data, some discover that a carbocation rearrangement occurred, resulting in isolation of only one product despite starting from a pair of isomeric reagents. This laboratory provides students with the opportunity to engage in a range of laboratory and problem-solving skills, and thus is designed to be performed toward the end of a two-semester organic chemistry sequence.

13C NMR Analysis of an Aqueous Electrophilic Aromatic Substitution (Synthesis of β-Resorcylic Acid)

“…13 C NMR has been used in conjunction with electrophilic aromatic substitution reactions, in both structural confirmation and alternative uses. , 13 C NMR is well-suited for our purposes because it allows us to observe each of the nonequivalent carbon atoms in a molecule as a singlet peak in its spectrum. If each carbon is unique, then the number of signals equals the number of carbons; if the molecule has an axis of symmetry, then the number of unique carbons decreases, as does the number of carbon signals. , In its most straightforward application, 13 C NMR can allow us to determine whether additional carbons (e.g., a carboxyl group) have been added during the reaction illustrated in Scheme .…”