Systematic variation of the substrate structure in the enantioselective hydrogenation of alpha, beta-unsaturated carboxylic acids over cinchonidine-modified Pd catalysts indicated that aryl substituents in beta position changed the adsorption mode of the substrates on the metal surface and eventually the configuration of the products formed in excess as compared to aliphatic substrates. The configuration of the products formed in excess by hydrogenation of eight alpha,beta-unsaturated carboxylic acids, of which two have not been described yet, indicated that the substrates hearing aromatic ring in P position were adsorbed on the opposite face of the C=C group compared to acids having aliphatic group in P position. (c) 2004 Elsevier B.V. All rights reserved.