The functionalization of monolayers of mercaptopropanol (MPL) and mercaptopropanoic acid (MPA) adsorbed onto surfaces of gold has been studied using X-ray photoelectron spectroscopy and contact angle goniometry. The terminal hydroxyl goups of the MPL monolayers were derivatized with the vapor from either trifluoroacetic anhydride, pentafluoropropanoic anhydride, or heptafluorobutyric anhydride to yield highly hydrophobic, CF3 functionalized surfaces. For the MPA monolayers the carboxylic acid groups at the surface were derivatized by reaction with the vapor from trifluoroethanol, pyridine, and di-tert-butylcarbodiimide. This resulted in only similar to 60% of the surface carboxyl groups undergoing reaction in contrast to the 100% derivatization of poly(acrylic acid), indicating a difference in reactivity of these two materials.