Using in situ generated iodine fluoride as the reagent, bromine can be replaced by fluorine at carbocation-sustaining sites. Iodine fluoride or, being its operational equiv., the mixt. of N-iodosuccinimide and triethylamine tris(hydrogen fluoride) reacts with tertiary and benzylic bromoalkanes to afford the resp. fluoroalkanes in moderate-to-excellent yields. In contrast, primary bromoalkanes are virtually inert under identical conditions. Secondary bromoalkanes do not react either unless the heterolytically generated cationic intermediates benefit from non-classical resonance stabilization. [on SciFinder (R)]