This paper describes the synthesis of phenol-terminated monolayers formed by the chemisorption of precursor trichlorosilanes to silicate substrates and subsequent in situ chemical transformations. A trichlorosilane containing an Ii-carbon polymethylene spacer and methyl-protected phenol was synthesized. The corresponding o-chlorophenol system was also synthesized. The monolayer structure was studied by a combination of reflectance FTIR,-X-ray reflectometry, solid-state C-13 NMR spectroscopy, and water contact angles. Reaction of the monolayers with BBr3 produced phenol-terminated monolayers. Data obtained by contact angle titration using buffered solutions with pH values in the range of 1-14 was consistent with ionization of the surface-immobilized phenol groups. The o-chlorophenol group exhibited a decrease in contact angles at lower pH values, which is consistent with a more acidic surface. The phenol and o-chlorophenol exhibited pK(1/2) greater than or equal to 12.5 and greater than or equal to 12, which are at least 2.5 pH units higher than the solution pK(a) values.