Ethylene chemisorption on model copper chloride [CuxCly, CuxCly(OH)z] and supported copper chloride [CuxCly(OH)z/Alr(OH)s] clusters was examined using spin-polarized gradient corrected density functional theory. Both the mode and the energy of ethylene chemisorption are affected by the oxidation state, the coordination number, and the ligand field at the Cu center. In addition, the specific location of the vacant site (atop vs in-plane), adsorbate orientation, and support interactions were also found to be important in dictating the strength of the bond between ethylene and Cu. Ethylene weakly physisorbs atop a central Cu atom, in an axial ligand position, with an energy of less than 2 kcal/mol on the fully saturated Cu2+ adsorption site. The more favorable adsorption state is one which contains a defect site within the CuxCly plane. Ethylene strongly chemisorbs at this site, with its CC bond oriented perpendicular to the CuxCly plane, with an energy of −18.7 kcal/mol. Two intermediate states also exist w...