The products formed from the thin-layer voltammetric electrooxidation of methanol, ethanol, and isopropanol on platinum under anhydrous conditions and in concentrated acidic aqueous solutions are examined by means of real-time FTIR spectroscopy. For anhydrous methanol and ethanol in 0.1 M LiClO 4, 1,1-dimethoxymethane and 1,1-diethoxyethane, respectively, constituted the major products along with methyl formate in the former case, as deduced from their characteristic infrared vibrational features. No adsorbed CO, nor CO 2 product, were formed from either solvent in the absence of water, although the addition of solution CO yielded high CO coverages as discerned from the characteristic potential-dependent C-O vibration at ca 2070–2090 cm −. Addition of even small proportions (20–30%) of aqueous HClO 4 yielded marked changes in the electrooxidation kinetics and mechanisms, as discerned quantitatively from the potential- (and time-) dependent vibrational band intensities. For methanol under such conditions, dimethoxymethane ceases to be formed and adsorbed CO and product CO 2 appear in increasing quantities as the water content increases. Methyl formate, however, remains as a significant product down to methanol concentrations of about 0.2 M. Addition of acidified water to ethanol also yields adsorbed CO, although the CO 2 produced arises chiefly from electrooxidation of only the initially adsorbed CO layer. Substantial quantities of acetaldehyde are also formed, the extent of further electrooxidation to acetic acid increasing as the aqueous ethanol concentration is decreased. Electrooxidation of isopropanol yields only acetone in both anhydrous and aqueous environments. In the presence of nitrate ions under anhydrous conditions, however, electrooxidation of all three alcohols yield nitrate ester coupling products.