Activity coefficients at infinite dilution gamma(infinity) of 28 organic compounds in eight room-temperature ionic liquids of the family of 1-propyl boronic acid-3-alkylimidazolium bromide and 1-propenyl-3-alkylimidazolium bromide (with alkyl = methyl, octyl, decyl, or dodecyl) were determined at 323.15 K using inverse gas chromatography. Using all the available gamma(infinity) data, the selectivities at infinite dilution S-12(infinity) were determined. Indeed, such values are extremely useful for the design and the optimization of separation processes.