The irreversible adsorption of several C-3 alcohols, 1-butanol, and ethene on platinized platinum has been studied with Fourier transform IR spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) in perchloric acid electrolyte. Apart from 2-propanol, all studied alcohols display C-C(O) dissociative adsorption as the only pathway active in the formation of irreversible adsorbates. 1,2,3-Propanetriol is the only compound that is fully converted to adsorbed CO, while all other primary alcohols generate hydrocarbon adspecies in addition to CO. No further C-C bond breaking is observed in these hydrocarbon adspecies, which were found to be highly dehydrogenated. The hydrocarbon species can be fractionally hydrogenated off the surface to form corresponding gaseous compounds. 2-Propanol and ethene do not undergo C-C dissociation to form CO but are dehydrogenated considerably. For 2-propanol and ethene it was found that a small amount of oxygen incorporation occurs on the C-1 position, followed by decarbonylation to form CO.