LINEAR ENTHALPY-SPECTRAL SHIFT CORRELATIONS FOR 1,1,1,3,3,3-HEXAFLUORO-2-PROPANOL

Calorimetric (enthalpy), OH frequency shift, and hydrogen-bond chemical shift data are reported for the 1,1,1,3,3,3-hexafluoro-2-propanol acid-base interaction with a variety of Lewis bases. The following quantitative correlations are found: ∆H (±0.2) = (0.0115)∆v + 3.6 and ∆H(±0.3) = (0.886)∆ + 3.6. The comparison of the data for the fluoro alcohol with those for phenol show the former to be the stronger hydrogen-bonding acid, regardless of the experimental quantity used to measure acidity. Several reliable linear correlations are found which can be used to compare the sensitivities and determine the compatibility of the three indices of acid-base interaction. The linear relationships, and in particular the nonzero intercepts, have been interpreted by an elaboration of the Lippencott-Schroeder model for hydrogen bonding. Application of this model to our data and that for phenol demonstrates the competative relationship between OH elongation and HB formation for each experimental parameter. The role of R, in ROH, in controlling the balance between these two processes is brought out by this analysis and is shown to be different for the three experimental quantities. The enthalpy data are used to characterize the acidity of the fluoro alcohol in terms of the E, C parameters of Drago and Wayland; the E and C values are useful in a discussion of the low enthalpy found for the soft donor diethyl sulfide. An attempt is made to determine the acidity leveling of the fluoro alcohol by diethyl sulfide, but the three experimental indices of acidity are found to be of different sensitivities to this leveling. © 1969, American Chemical Society. All rights reserved.