Abstract: The present invention relates to a process for the synthesis of "oxo" products or their derivatives consisting of hydrocarbon compounds containing carbonyl and/or hydroxyl groups, characterized in that a hydrocarbon substrate containing an unsaturation, such as an alkene, is reacted with reactants consisting of a mixture of hydrogen and carbon monoxide, the reaction taking place after bringing the substrate into contact with the neutral activated species of the mixture of reactants activated to the plasma state.In particular, the present invention relates to a process characterized in that an alkene is reacted to obtain a mixture containing the aldehyde and the alcohol resulting from the fixation on the double bond of the alkene of, respectively, a group ##STR1## or its group ##STR2## obtained by reduction, or only one of these two components by separating it from the mixture.