COMPARISON OF THE ORDERS OF GAS-PHASE BASICITIES AND AMMONIUM ION AFFINITIES OF POLYETHERS BY THE KINETIC METHOD AND LIGAND-EXCHANGE TECHNIQUE

The orders of relative gas-phase basicities and ammonium ion affinitie s of a series of polyethers obtained by application of the kinetic met hod and ligand exchange technique are compared to evaluate the discrep ancies of results between the two techniques. The order of gas-phase b asicities determined by the ligand exchange technique in a quadrupole ion trap agrees with the order established previously by Kebarle using equilibrium methods in a high-pressure mass spectrometer. The order o btained by the kinetic method in a triple quadrupole mass spectrometer varies for the ranking of one polyether (12-crown-4), and this discre pancy is attributed to a difference in the rates of the competing diss ociation pathways from the triethylene glycol dimethyl ether/12-crown- 4 proton-bound adduct, owing to a substantial variation in the flexibi lities of these two ethers. For the order of gas-phase ammonium ion af finities, the kinetic method results agree overall with the ligand exc hange results; however, the order of ammonium ion affinities for tetra ethylene glycol dimethyl ether and 15-crown-5 could not be differentia ted by the ligand exchange method because of the rapidity of ammonium ion transfer between the two polyethers in both directions.