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=(ηy+ηx)ωbωa+ log K0 where ηy and ηx represent the nature of the functional group of the base and acid, respectively, ωb and ωa 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 ωb 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 ηx.