The liquid-phase hydrogenation of 26 aromatic nitro compounds on heterogeneous Pd/C and Pd/Al2O3 catalysts was studied under mild conditions (the hydrogen pressure 0.1 MPa, 45 degreesC, ethanol). The rates of the reduction of nitro compounds on both catalysts are close, and the changes in the structure of the substrate molecule affect the hydrogenation rate in an almost identical manner. Based on quantum-chemical calculations on the substrate molecules, relationships describing the electronic effect of substituents on the hydrogenation rate were proposed.