13C NMR differences of chemical shifts (δx — δH) of allyl carbon atoms in a series of (1,2-bis(diphenylphosphino)ethane)(η3-1-(4-X-phenyl)allyl)palladium tetrafluoroborates, X ranging from NO2 to OMe, correlate very well (r > 0.994) with σ Hammett constants. However, 31P NMR differences of the ligand cis and trans phosphorus atoms correlate well with σ and with σ+, respectively. These data indicate that the positive charge density of the cation is localized mainly in the P—Pd—P region. © 1995, American Chemical Society. All rights reserved.