Hydrogen bonding in some adducts of oxygen bases with acids. Part IV. Basicity in hydrogen bonding and in ionisation

Abstract

The ionisation constants of several sulphoxides, phosphine oxides, selenoxides, triphenylarsine oxide, and pyridine 1-oxides have been determined in acetic acid by spectrophotometric titration with perchloric acid. The ionisation constants are compared with the hydrogen-bonding X–H stretching-frequency shifts of several proton donors of different acidity ranging from thiocyanic acid to phenylacetylene. The sequences of basicities by ionisation and by proton acceptance in hydrogen bonding correspond to each other only for strong acid X–H infrared shifts and other spectral symptoms of hydrogen bonding. Structural factors determining the ionisation constants of the oxo-bases are discussed as well as the differences between these and the amines in ionisation and in hydrogen bonding behaviour, respectively.