Linear Enthalpy–Spectral Shift Correlation for Perfluoro-tert-butyl Alcohol

Calorimetric enthalpy data and infrared OH frequency shifts are reported for the acid–base interaction of perfluoro-tert-butyl alcohol with a variety of Lewis bases. A reduced adduct solvation by CCl₄ plus an excessive acid solvation leads to lower enthalpies measured in CCl₄ solution than in hexane solution. Reaction enthalpies with six donors in hexane were used to evaluate the E_a and C_a parameters for perfluoro-tert-butyl alcohol. Seven other donor enthalpies were calculated using the double scale enthalpy equation. The following correlation was found: ΔH (±0.2) = 0.0106Δv + 3.9. This correlation along with ΔH vs. ΔH correlations with 2,2,2-trifluoroethanol, 1,1,3,3,3,3-hexafluoro-2-propanol, and phenol indicates that van der Waals repulsions are of least importance in the perfluoro-tert-butyl alcohol reactions. The slopes and intercepts of these relations, like the E_a and C_a parameters, reveal the relative electrostatic and covalent contributions in the formation of a hydrogen bond for each of these alcohols. The data adhere nicely to a single-scale enthalpy equation (ΔH_a = α_Aβ_B) and an α vs. σ∗ plot. This fit provides good evidence for negligible acid–base steric interactions in the perfluoro-tert-butyl alcohol reactions.