The Finkelstein reaction is an organic reaction where an alkyl halide is converted into another alkyl halide by reacting with a metal halide salt. This is an equilibrium process and it is driven forward by taking advantage of the poor solubility in acetone of the newly formed metal halide salt (Le Chatelier's principle). The mechanism for this reaction is a simple, single-step bimolecular nucleophilic substitution reaction (SN2) which like all SN2 reactions occur with inversion of stereochemistry.
Finkelstein, H. Ber. Dtsch. Chem. Ges. 1910, 43, 1528–1532.