Hydroprocessing of substituted benzenes like aniline; phenol, diphenylsulfide and chlorobenzene was performed in a batch reactor over unsupported transition metal sulfides, namely Co, Ni, Nb, Mo, Ru, Rh, Pd and W sulfides at 280 degrees C and 70 bar of hydrogen pressure. Under these experimental conditions, diphenylsulfide and chlorobenzene mainly react through initial hydrogenolysis of the carbon-substituent bond whereas aniline and phenol react through initial hydrogenation of the aromatic ring. Such a behavior was already reported for conventional sulfided cobalt- and nickel-molybdenum alumina supported catalysts. Nevertheless, these new results confirm the preponderant influence of mesomeric effects on the reactivity of organic models toward sulfided catalysts. In addition to the results obtained over the supported bimetallic sulfides, it was found from quantum chemical calculations that the hydrogenolysis rate constants correlate with the rr-electron density on the carbon bearing the substituent and with the overall calculated pi-electron transfer between the substituents and the benzene ring. It is thus assumed that hydrogenolysis of carbon sp(2)-substituent bonds results from the attach, by a soft nucleophilic species like a hydride ion, on the carbon bearing the substituent.