Using differential electrochemical mass spectrometry, the adsorption of ethene, ethanol and cyclohexene on mono- and polycrystalline Pt electrodes was studied. Experiments in (H2O)-O-18 showed that a part of the adsorbed ethene molecules contains oxygen. Ethanol mainly dissociates upon adsorption, yielding an adsorbed GO-like species and a CHx fragment which can be cathodically desorbed as methane. From a polycrystalline Pt electrode, adsorbed cyclohexene can be cathodically desorbed as benzene and cyclohexane in the same ratio as adsorbed benzene, and is therefore most likely to be identical to adsorbed benzene; cyclohexene adsorption on Pt(111) and Pt(110) mainly yields an oxygenated species in a similar reaction as that which occurs for a part of the adsorbing ethene.