The reactive sites of self-assembled monolayers (SAM) formed by substituted thiolalkyl chains have been predicted in the case of the pure mercaptoundecane acid, for the pure mercaptoundecane alcohol, and the mixed 1:1 SAMs. The differences in reactivity between the different SAM domains (pure and mixed) would enable selective substitution of the head groups leading to a better understanding of the dispersion of the adsorbed molecules on the SAM surface. Selective reactivity was predicted in order to investigate the homogeneity of the mixed SAMs, and in view of designing new SAM surfaces. The results are discussed in terms of the electrostatic potential and the Fukui function. (c) 2008 Wiley Periodicals, Inc.