Hydrogen‐bonding 8. Possible equivalence of solute and solvent scales of hydrogen‐bond basicity of non‐associated compounds

Abstract

Abstract Using the solvatochromic indicator method, a scale of solvent hydrogen‐bond basicity, β 1 (General), has been set up using a series of double regression equations, for 11 aniline‐type indicators. A similar solvent scale, β 1 (Special), has been constructed by the homomorphic comparison method using only results by Laurence et al. on the indicators 4‐nitroaniline and 4‐nitro‐ N , N ‐dimethylaniline. Results are available from our previous work on a general solute scale, β , and we have also obtained a special solute scale, β 2 (p K HB ) from available log K values for hydrogen‐bond complexation of bases with 4‐fluorophenol in CCl 4 . However, the two solute β 2 scales are virtually identical. It is shown that there is a general connection between β 1 (General) and β , with r = 0·9775 and s.d. = 0·05 for 32 compounds, and between β 1 (Special) and β , with r = 0·9776 and s.d. = 0·06 for the same 32 compounds. The latter correlation over 60 compounds yields r = 0·9684 and s.d. = 0·07. However, there are so many compounds in these regressions for which the differences in the solvent and solute β values are larger than the total expected error of 0·07 units that the use of β 1 to predict β 2 or vice versa is a very hazardous procedure. About 70 new β 1 values obtained by the double regression method are also reported.