Abstract Carbon-13 NMR investigations of olefins adsorbed on synthetic faujasites (NaX, NaY, TIX) and on commercial alumina catalysts impregnated by Na + ions suggest the existence of a specific interaction between the olefins and Na +. The dominant effect on carbon-13 line shifts in the highly resolved spectra is attributed to olefin—sodium bonds. ln Na +-containing solutions no influence on carbon-13 lines due to olefin complexing has been found. Measurements on silver—olefin complexes in solution and in the adsorbed state yield comparable chemical shifts indicating a similar structure for the complexes in both cases. In addition, the first reported studies of the mechanism of the isomerization of n-butene by carbon-13 NMR methods are described.