The effects of defect sites and coadsorbed iodine atoms on the chemistry of alkyl groups with two to four carbon atoms on copper surfaces have been studied by temperature-programmed reaction (TPR). The primary reaction pathway for the adsorbed alkyl group both in the presence and absence of defects and iodine atoms is beta-hydride elimination. Because desorption is not (under most conditions) the rate-determining step in the evolution of the product from the surface, the rate of the surface beta-hydride elimination reaction could be monitored by TPR. Neither surface defects nor low coverages of coadsorbed iodine significantly affect the beta-elimination rate. For high coverages of iodine, however, the rate of beta-elimination by 5-10% of the adsorbed alkyl groups is decreased by over five orders of magnitude (T-rxn = 385 K versus 230 K). The reaction kinetics together with observations from low-energy electron diffraction studies suggest that the dramatic inhibition of the beta-elimination rate for high iodine coverages is due to cages of immobile iodine atoms that surround the alkyl groups and prohibit hydrogen transfer to the surface.