Glassy carbon (GC) surfaces are functionalized exploiting the electrochemical reduction of asymmetric iodonium salts of the general formula [4-Z-C6H4-I+-C=C(CH2)(4)Cl, Z = NO2, Br, F, H, or CH3]. The range of Z groups was selected aiming to examine the C-aryl-I bond energy as a function of the "electron withdrawing/electron donating" ability of the Z-group, with the ultimate purpose of controlling the alkynyl/aryl grafting ratio. The electroreduction mechanism and the characteristics of the grafted surface are studied by means of cyclic voltammetry and X-ray photoelectron spectroscopy. It is shown that the alkynyl/aryl grafting ratio decreases with the increasing electron withdrawing nature of Z, which induces a weakening of the C-aryl-I bond. Ab initio DFT vertical electron affinities (EA(v)) allowed to rationalize the electroreduction potentials of both the bulk and surface functionalised redox couples. Moreover, the alkynyl/aryl grafting ratio is assessed, at a molecular level, on the basis of ab initio DFT potential energy surfaces. (C) 2013 Elsevier B.V. All rights reserved.