A Discovery-Based Experiment Involving Rearrangement in the Conversion of Alcohols to Alkyl Halides

摘要

The use of permanent magnet 13C NMR in large-section first-semester organic chemistry lab courses is limited by the availability of experiments that not only hinge on first-semester lecture topics, but which also produce at least 0.5 mL of neat liquid sample. This article reports a discovery-based experiment that meets both of these criteria. Students convert three alcohols to alkyl halides under acidic conditions and record the 13C NMR spectrum in each case. By comparing the number of resonances observed with the number of resonances predicted for each possible product, they conclude that (i) with 1-propanol there is no carbocation rearrangement, (ii) with 2-pentanol there is a considerable degree of secondary-to-secondary carbocation rearrangement, and (iii) with 2,4-dimethyl-3-pentanol all of the alkyl halide formed is the result of a secondary-to-tertiary carbocation rearrangement.