THE NATURE OF FIELD EFFECTS AND THEIR FALL-OFF WITH DISTANCE - THE ACIDITY OF SUBSTITUTED QUINUCLIDINIUM AND BICYCLOOCTYLAMMONIUM IONS

Gas-phase acidities are reported for series of substituted quinuclidinium and bicyclo [2.2.2] octylammonium ions. Ab initio calculations are also reported for these equilibria at the STO-3G and 3-21G (for the quinuclidines) bases and can be used to extend the results. pK(a) values obtained for the bicyclooctylammonium ions are compared with previously reported results for the quinuclidinium ions. The results, as a whole, are considered together with similar values obtained for other saturated systems, to look at the varying transmission of field effects with distance. The falloff observed between the two series in the gas phase is considerably less than expected from simple electrostatics. In contradication with a recent claim, it is also shown that field effects, as measured by the parameter sigma-F, give a good measure of the effect of the substituents in each series compared with a combination of resonance and electronegativity effects.