= Solution
tert-Butoxide removes the acidic <hydrogen> from $\mathrm{PhCH(OPh)CN}$. The resulting <carbon> anion is stabilized by the nitrile group and the phenyl substituent. It attacks the aromatic <carbon> bearing fluorine, giving a Meisenheimer addition intermediate. Ring pi bonds shift toward the para <nitro group>, where the negative charge can be delocalized onto <oxygen>.
Loss of fluoride restores <aromaticity> and gives \b[$\mathrm{p{-}NO_2C_6H_4{-}C(Ph)(OPh)CN}$]. This is an addition–elimination <nucleophilic aromatic substitution>. The phenoxy group remains attached to the incoming <carbon>. The ipso aromatic <carbon> already has a leaving group, so rearomatization can occur by fluoride departure without removing <phenoxide>. Acid workup neutralizes residual anions; it is not a separate step that replaces the aryl fluoride.
\Image[/past-exam-of-the-chemistry-b-course-of-the-university-of-cambridge/2024/paper-1-aromatic-substitution.png]
{title=Contrasting fluoride substitution and vicarious hydrogen substitution}
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