Relation between the formation constant and the local structure of various bases and reference acids for the 1 : 1 hydrogen-bond complexation in aprotic solvents

Abstract

For the 1 : 1 hydrogen-bond complexation of various bases against reference acids in aprotic solvents, the formation constant has been correlated with the local structure of acids and bases by regarding a base or an acid as composed of two local structural units, a functional group and a residual moiety. The following equation has been introduced to correlate log K, where K is the formation constant with the local structures: log K=(η_y+η_x)ω_bω_a+ log K₀ where η_y and η_x represent the nature of the functional group of the base and acid, respectively, ω_b and ω_a represent the electronic effects of the residual moiety of the base and acid, respectively, and log K₀ is a constant.

Family-independent and -dependent behaviour observed for log K of 26 bases against p-fluorophenol, phenol and 5-fluoroindole in CCl₄ are reasonably interpreted by applying the above equation. Formal ω_b values of the bases have been evaluated. It has been pointed out that Maria–Gal's angle θ which represents the electrostatic: covalent ratio of hydrogen bonding reflects the nature of the functional group of reference acids, as well as η_x.