Adsorption of 1-phenyl-1,2-propanedione (A), a widely studied molecule in heterogeneously catalyzed enantioselective hydrogenation, and 2,3-hexanedione on a Pt(111) surface was studied using density functional theory. A cluster consisting of two slabs and 31 Pt atoms was used as a model for the catalyst. The results revealed the origin of observed regioselectivity in the hydrogenation of carbonyl groups C1 = O1 and C2=O2 of A and the lack of regioselectivity in the case of 2,3-hexanedione on Pt catalysts. The adsorption modes of A in which the C1 = O1 carboryl group next to the phenyl ring is activated toward hydrogenation (eta(2)(C1=O1) adsorptions) are more stable than the corresponding adsorption modes CI=O1 C2=O2 adsorption). This indicates that the catalyst surface is covered mainly by reaction intermediates where the C2=O2 group is activated (eta(2) leading to the hydrogenation of the carbonyl group C1=O1 and eventually regioselectivity, presuming that the hydrogenation rates of CI=01 and C2=02 are of the same order of magnitude. The adsorption energy of 2,3-hexanedione does not depend on which of the carbonyl groups is adsorbed as eta(2)-mode, and thus the hydrogenation on Pt is not regioselective, as has been observed experimentally. Thus the regioselectivity in the hydrogenation of A and 2,3-hexanedione can be explained by the interactions between the substrate and the metal surface. (c) 2006 Elsevier Inc. All rights reserved.