Abstract Perfluoro-n-heptyl iodide and 1–1.5 molar equivalents of n-butyllithium in diethyl ether or halide-free diethyl ether/pentane undergo 40–50% halogen-metal exchange below− 90 and form a stable heterogeneous system. The stability of the perfluoro-n- heptyllithium present is attributed to its association with perfluoro-n-heptyl iodide. Such a mixture reacts only slowly with acetaldehyde below− 90 to give a low yield of 1-(perfluoro- ...