Ab initio calculations on hydrogen bonding in alcohols: Dimers of CH3OH, CH3CH2OH, and CF3CH2OH

Abstract

Ab initio calculations on a series of alcohol dimers including (CH3OH)2, (CH3CH2OH)2, and (CF3CH2OH)2 have been carried out to compare the effects of various substituents on the hydrogen bond energies and structures and to correlate the results with the wealth of new experimental data on them. Calculations were done with the minimal STO-3G basis set. The methanol and ethanol dimers both have nearly linear hydrogen bonds. The ethanol dimer is also similar in energy to the methanol dimer. Dimers involving both the g-staggered and t-staggered isomers of 2,2,2-trifluoroethanol were considered. The g-staggcred isomer is more stable than the t-staggered isomer by 0.7 kcal/mol and has an intramolecular bond. The dimer of the t-staggered isomer was found to have a linear hydrogen bond as in the methanol and ethanol dimers with a similar hydrogen bond energy. In contrast, the dimer of the g-staggcred isomer has a cyclic structure which is more stable by about 0.5 kcal/mol. The results are consistent with experimental measurements of the gas phase enthalpies of association of alcohols.