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

Article abstract of DOI:10.1139/v82-136

Proton transfer equilibria (B1H(+) + B2 <-> B1 + B2H(+)) and NO(+) transfer equilibria (B1NO(+) + B2 <-> B1 + B2NO(+)) 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 ΔG⁰ and from van't Hoff plots, ΔH⁰ and ΔS⁰.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 of 4.The position of the F substituent on toluene has a marked effect on proton affinity but no effect on NO(+) affinity.The latter appears to be responsive only to the inductive effect.