We have developed electrophilic aromatic substitution reactions, some involving carbocation rearrangements, and have implemented them successfully in the undergraduate teaching laboratory. Our work is based on the known Friedel-Crafts alkylation of 1,4-dimethoxybenzene with t-butanol. We extended this reaction into an undergraduate discovery laboratory format in which faculty may choose from seven alcohols that students transform into products. Students then solve the structures of their products using GC/MS, 1H NMR, and 13C NMR. Two of our reactions involve a backbone rearrangement in the alkylation of 1,4-dimethoxybenzene: a [1,2]-hydride shift with 3-methyl-2-butanol (R = H) that students compare with 2-methyl-2-butanol and a [1,2]-methyl shift with 3,3-dimethyl-2-butanol (R = CH3) that students compare with 2,3-dimethyl-2-butanol. Working in pairs, students with a matched set of alcohols generate the same product, adding an important level of problem-solving to this discovery-based experiment. We further extended this method to include two more tertiary alcohols (3-methyl-3-pentanol and 3-ethyl-3-pentanol) and, importantly, eliminated tempting alcohols that, unfortunately, do not react under these conditions. In summary, identical reaction conditions were used for all four alcohols such that students provided with 1,4-dimethoxybenzene and one of seven alcohols can participate in a discovery laboratory experiment that requires careful analysis of instrumental data (and not reaction conditions) to determine the identity and structure of their products.

Carbocation rearrangements in the undergraduate laboratory: GC/MS and NMR deduction of products from electrophilic aromatic substitution in a discovery laboratory experiment

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.