Stabilities of Halonium Ions from a Study of Gas-Phase Equilibria R(1+)+XR'=(RXR')(1+)

Article abstract of DOI:10.1021/ja00299a002

The gas-phase ion equilibria R(1+)+B=RB(1+), where R(1+)=Et(1+), i-Pr(1+), c-Pe(1+), t-Bu(1+), 2-Me-2-Bu(1+), and 2-Nb(1+) and B=CH3Cl, CH2Cl2, CHCl2, CHCl3, SO2F2, CF3H, and CF4 were determined in a pulsed electron beam high pressure mass spectrometer. van't Hoff plots provide ΔG⁰₃₀₀, ΔH⁰, and ΔS⁰.For the chloronium ions the following trends were observed.The bond energy D(R(1+)-ClR₀), where R(1+) changes and R₀ is constant, decreases with increasing electronic stabilization of R(1+), i.e., in the order Me(1+), Et(1+), i-Pr(1+), c-Pe(1+), t-Bu(1+), Nb(1+).The same order was observed earlier in this laboratory for D(R(1+)-Cl(1-)), i.e., the chloride affinity of R(1+).However, the changes of D(R(1+)-ClR₀) for R(1+)=2-Me-2-Bu(1+), Nb(1+), and t-Bu(1+) are very small.This means that little differential, specific nucleophilic solvation of these ions in solution is to be expected when solvents of low nucleophilicity like CH2Cl2 and SO2ClF are used.The bond energies D(Me(1+)-ClR) increase in the order R=Me, Et, i-Pr, t-Bu.The bond energies D(t-Bu(1+)-B) decrease in the order B=C2H5Cl, CH2Cl2 ca.CH3Cl, CCl3H, SO2F2, CF3H, CF4.The significance of these trends is discussed.