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, β₂^H and β₂^C, and a steric hindrance parameter, E_s· β₂^H and β₂^C 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 E_s parameter characterizes the steric effect experienced by the solute acceptor site. It is shown that retention correlates very strongly with β₂^Hand less strongly with β₂^C. The log k′ values need only two descriptive parameters, i.e., β₂^Hand E_s 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.