Electrophilic aromatic substitution (EAS) reactions form the basis for several experiments in undergraduate organic chemistry laboratory courses. Among the more commonly used EAS reactions are nitration, bromination, and Friedel-Crafts acylation. Using benzene with activating ortho-para directing substituents, these reactions often give predominantly the para substituted product due to steric crowding at the ortho positions. This may leave students skeptical that the supposed 2:1 ortho:para statistical preference is ever achieved in practice. As one example, we have developed an EAS reaction for the electrophilic fluorination of acetanilide, 1, that yields a mixture of ortho-(2), para-(3), and difluorinated (4) derivatives with the ortho and para in very close to the statistical 2:1 ratio. Each of the products is readily distinguishable using 19F-NMR. We will provide evidence that both high-field (300 MHz) and low-field (60 MHz) instruments can provide spectra that are quite pedagogically acceptable.

Fluorine – the neglected halogen in the undergraduate organic lab – electrophilic aromatic substitution

255th National Meeting (2018)

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