Liquid chromatographic study of solute hydrogen bond basicity

The purpose of the present work was to investigate a liquid chromatographic method for the measurement of relative hydrogen bond basicities of dilute species. This type of determination cannot be done with conventional reversed-phase liquid chromatography due to the silanophilic interactions of basic solutes with the silica packing material. The studies were done on a polymeric stationary phase with pendant phenol groups that act as powerful hydrogen bond donors. Solute retention was evaluated in terms of two hydrogen bond basicity scales, beta 2H and beta 2C, and a steric hindrance parameter, Es. beta 2H and beta 2C are basicity scales based on the free energy of forming 1:1 hydrogen bond complexes and the retention on a strong hydrogen bond donor gas chromatographic phase, respectively. The Es parameter characterizes the steric effect experienced by the solute acceptor site. It is shown that retention correlates very strongly with beta 2H and less strongly with beta 2C. The log k' values need only two descriptive parameters, i.e., beta 2H and Es, to give a good fit. As a whole, retention on the phenolic polymeric phase provides an efficient method for the measurement of relative hydrogen bond basicities.