STUDIES OF HYDROGEN-BONDING IN VAPOR-PHASE BY MEASUREMENT OF THERMAL-CONDUCTIVITY AND MOLECULAR-ORBITAL CALCULATIONS - 2,2,2-TRIFLUOROETHANOL

The thermal conductivity of 2,2,2-trifluoroethanol vapor was measured in a modified thick hot-wire cell between 338 and 385 K at pressures ranging from approximately 100 to 1300 Torr (13.3-1 73 kPa). Analysis of the data indicates that molecular association to form a dimeric species is the main source of the enhancement of the thermal conductivity of the vapor. The enthalpy of association of the trifluoroethanol dimer is -4753 cal/mol and the entropy of association is -18.73 cal/mol K. Ab initio calculations were carried out on several rotational isomers of trifluoroethanol and on four possible dimer structures. The most stable dimer is a cyclic structure involving the gauche-staggered isomer of trifluoroethanol. An extra hydrogen bond due to the presence of the fluorines enhances the stability of the dimer compared to the methanol dimer. © 1978, American Chemical Society. All rights reserved.