We evaluate the mechanism of Cu deposition in the presence of additives of different chain lengths to provide design guidelines for electroplating additives in the specific context of Cu electroplating. The effects of chloride and a series of sulfonic acid additives were assessed using a combination of electrochemical and Raman spectroscopic methods. Rotating disk linear sweep voltammetry revealed the influence of these additives on the bulk concentration of Cu⁺ and on the exchange current densities of the reduction of Cu²⁺/Cu⁺ and Cu⁺/Cu. We then used in situ shell-isolated, nanoparticle-enhanced Raman spectroscopy to correlate the additives’ effects on deposition kinetics with their chemical structures at the electrode surface. The combination of these methods suggests that effective Cu electrodeposition acceleration processes require: 1) direct tethering of mercaptoalkylsulfonate species to the electrode, 2) partial desolvation of Cu²⁺ by the sulfonate group to minimize its solvent reorganization energy, and 3) stabilization of Cu⁺ adjacent to the electrode surface by addition of halide.