Dimethylanilines, basicity constants

The basicity constants of WA-dimethylaniline and pyridine are almost the same, whereas 4-(A V-dimethylammo(pyridine is considerably more basic than either. 

They clearly indicate that the pf is not the same as solvent hydrogen bond basicity, /ii, because the pf value treats the solvent as a solute in the chemical interactions, and that the pf and fli scales are relatively collinear but not interchangeable . (The latter scale is based on the comparison of the indicators p-nitroaniline and p-nitro-Af, N-dimethylaniline.) Neither is the value connected to solute proton-transfer basicity . They have established that this pf value is relatively constant for homologous series of solvents, and that substituents on the parent structure of the solvent do not overly influence the pf value in terms of inductive or polar effects, unless the substituent is halogenated, in which case the will decrease. Chain branching of the parent also has little effect on the pf value. This makes it possible to predict average P2 values for solutes whose ATg values are not known. Correlations of kinetic data with pf are not always accurate because the pf parameter does not take into consideration solvent size, which can lead to steric hindrance of hydrogen bond formation . ... 

The basicity, expressed as acidity constants of the conjugated acids (pATa) of the R Pl(pyrrolidino) iminophosphoranes (40) have been determined in tetrahydrofur-an by potentiometry complemented by conductometric measurements. Comparison with other bases on an absolute scale of basicity established for this solvent covered a range from 7.4 for dimethylaniline to 21.7 for (40e). ... 

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