Spectroscopic studies of hydrogen bonding: Hexafluoroisopropanol

Abstract

The shifts of the OH stretching frequency and OH proton shielding constant of 1,1,1,3,3,3-hexafluoro-2-propanol upon hydrogen bond formation are reported. Oxygen, nitrogen, and sulfur donors of various types were used as Lewis electron pair donors. A correlation between the frequency and shielding constant changes is found and compared with those for phenol and 2,2,2-trifluoro-ethanol. The use of this data to index the acidities of these alcohols and the magnitides of the acid-base interactions is discussed. The influence of the substituent on the nature of chemical shift, frequency correlations is examined. The nonzero intercepts of the chemical shift, frequency shift correlations are discussed in terms of the generalized Lippincott-Schroeder one dimensional model for hydrogen bonded adducts, from which the importance of donor to hydrogen charge transfer is inferred. The data also appear to require a correction of about 0.5 ppm to the proton chemical shift when the donor atom is sulfur. The diethylsulfide, hexafluoro-2-propanol OH frequency shift appears to be anomolously low by about 75 cm −1 and results in a spectroscopic reversal of base strength.