Molecular structure effects in catalytic hydrogenations on a group of noble metals (Pt, Pd, Rh) were discussed. The method of competitive hydrogenation allowed the assessment of the relation between the molecular structure and the rate of a surface reaction in parallel with the stability of the surface complex. Experimental results, presented as selectivity, reactivity and adsorptivity parameters, were interpreted by means of molecular modelling. This communication reviews the research work that has been carried out in the recent past, with intention to contribute to the general theory of molecular structure effects in heterogeneous catalysis.