A comparison of the relative binding energies of H⁺ and NO⁺ to aromatic and haloaromatic bases by high pressure mass spectrometry

Abstract

Proton transfer equilibria (BIH+ + B, e B , + B,H+)and NO+ transfer equilibria(B,NO+ + B, *B, + B,NO+) have been studied for the following bases B, benzene, toluene, o -, m -, and p-xylene. NO+ transfer equilibria for fluoro-and chlorobenzene have also been studied. Pulsed electron beam, high-pressure ion source mass spectrometry has been used to obtain the equilibrium constant K and hence the free energy changes AGO and from van't Hoff plots, AH0 and AS0. Entropy changes are in general much smaller for NO+ transfer than for H+ transfer but the magnitude of the changes in the proton affinity and NO+ affinity of toluene caused by a fluorine substituent is about the same, even though the absolute value of the proton affinity is greater by a factor of4. The position of the F substituent on toluene has a marked effect on proton affinity but noeffect on NO+ affinity. The latter appears to be responsive only to the inductive effect. [Traduit par le journal]

Ion-Molecule Equilibria, How and Why

“…High pressure techniques were used by Meot-Ner and coworkers [27], Franklin and co-workers [28], Tang and Castleman [29], Meisels et al, [30], Meot-Ner et al [31], Jennings and co-workers [32], Stone et aI. [33], Hiraoka et al [34], and McMahon and co-workers [35].…”

Gas-phase proton transfer in halogenotoluene mixtures. Evidence for a ‘dynamic’ ion structure

“…An independent study7 of other systems containing fluorotoluenes was carried out at 478 K. The basicities relative to m-fluorotoluene have been calculated from data given in ref. (7) and are listed in table 2. These data are in good qualitative agreement with the data obtained in this laboratory but lead to somewhat larger differences in the gas-phase basicities of the three isomeric fluorotoluenes.…”