Linear enthalpy-spectral shift correlations for 2,2,2-trifluoroethanol

A new calorimeter design is presented and calorimetric enthalpy data are reported for the acid-base interaction of 2,2,2-trifluoroethanol with a variety of Lewis bases. The following correlations are found : ΔH( ±0.13) = 0.0121 Δv + 2.70 and ΔH(±0.26) = 0.98Δ + 2.30. These correlations are compared with the similar data for phenol and 1,1,1,3,3,3-hexafluoro-2-propanol to reveal the relative abilities of the phenyl, trifluoroethyl, and hexafluoroisopropyl substituents to withdraw electron density from OH and to characterize their role in hydrogen bond formation. Other correlations such as ΔH vs. ΔH are instrumental in this regard as they give meaning to the ΔH vs. Δv correlations. All correlations can be interpreted within the framework of the Lippincott-Schroeder model of hydrogen bond formation. The data adhere nicely to a double-scale enthalpy (E and C) relation; in addition, a single-scale enthalpy relation (ΔH = αβ_B) is established which reveals substituent inductive effects and, in the cases of phenol and di-t-butylcarbinol, resonance and steric effects, respectively.