Molecular interactions in well characterized self-assembled alkanethiolate monolayers on Au(111) and Ag(111) are studied from reductive electrodesorption curves recorded in 0.1 M NaOH in a 95% methanol +5% water mixture to minimize the effect of hydrophobic forces. From the electrochemical and STM data and quantum DFT calculations, it can be concluded that the difference in peak potentials experimentally observed for the reductive desorption of a given alkanethiolate from the Ag(111) and Au(111) surfaces is determined by the energy to introduce an electron into the adsorbed alkanethiolate-metal species, the desorption energy of the alkanethiolate anion, and the solvent/metal interaction energy.