Possible reaction steps occurring when nitriles and hydrogen are simultaneously adsorbed on nickel have been investigated by means of semi-empirical extended Huckel calculations. The study of the reactivity has been carried out on Ni(100) : after the first hydrogenation step which principally yields imido ethylidene (CH3CH=N-), both adsorbed perpendicular and parallel to the metallic surface, we predict a competition between a second hydrogenation, which leads to a nitrene species (CH3CH2-N=) doubly bonded to the surface, and a coupling process involving a C-C bond formation. For each of these steps, activation energies have been estimated, and the stabilities of the a priori possible adsorbed forms of the intermediates have been compared.