The kinetics and stereochemistry of the protonation-induced unimolecularisomerization of (R)-1-D1-3-(p-fluorophenyl)butane have been investigated in the gas phase at 40−100 °C and 70−760 Torr. This process leads to the formation of the relevant meta and ortho isomers with partial racemization of the migrating sec-butyl moiety. Complete racemization is observed, instead, when the isomerization reaction