Crossed-beam experiments on the reactions of cyano CN(X2Σ+) and ethinyl C2H(X2Σ+) radicals with the unsaturated hydrocarbons acetylene, ethylene, methylacetylene allene and benzene have been carried out under single-collision conditions to investigate synthetic routes to form nitriles, polyynes and substituted allenes in hydrocarbon-rich atmospheres of planets and their moons. All reactions were found to proceed without an entrance barrier, to have exit barriers well below the energy of the reactant molecules and to be strongly exothermic. The predominant identification of the radical versus atomic hydrogen exchange channel makes these reactions compelling candidates for the formation of complex organic chemicals – precursors to biologically important amino acids – in Solar system environments and in the interstellar medium.