Ion-molecule association reactions involving cyano-compounds

The gas-phase equilibria for several ion-molecule association reactions involving cyano-compounds, as for example, HCNH+ + H2O in equilibrium HCNH+ X H2O, was determined using the NBS pulsed high-pressure mass spectrometer. A linear correlation is found between the bond dissociation energy ΔH0/sub D/ of the ion dimer and the difference ΔPA between the proton affinities of the proton donor and the proton acceptor (HCN and H2O, resp., in the case of reaction above). The correlation -ΔH0/sub D/ (kcal-mol-1) = ΔH0/sub D/ (O) - bΔPA for -NH+...NCR bonds yields the parameters (ΔH0/sub D/ (O),b) = (35.3, 0.34) and (27.2, 0.31) in amineH+ -nitrile and nitrileH+-nitrile systems, resp.; for RCNH+...O- bonds, (ΔH0/sub D/, b) = (28.5, 0.32) in nitrileH+-water systems; and for -OH+...Nbonds, (ΔH0/sub D/ (O),b) = (29.6, 0.33) in oxonium ions-HCN systems. The correlations are in accord with trends predicted by ab initio calculations of Desmeules and Allen