Grazing incident angle X-ray diffraction and linear sweep voltammetry were used to determine structure and reactivity of the Au(100) surface during the course of glucose, CO, and formaldehyde oxidations. The potential dependence of the diffracted intensity at the principal reconstruction peak was measured in HClO4 (for CO and glucose) and NaOH (for formaldehyde) solutions in the absence and in the presence of adsorption and oxidation of organic molecules. The oxidation occurs before or at the onset of the lifting of the reconstruction. No significant change in the kinetics of the reconstruction lifting or recovering is caused by the adsorption and oxidation of the above organic molecules. The more negative current peak potentials and the larger values of heterogeneous rate constants for the unreconstructed Au(100) surface indicate that the unreconstructed Au(100) surface is more active than the hexagonally reconstructed Au(100) for all three reactions.