CONFORMATIONAL INFLUENCE ON HYDROGEN-BOND

Thermodynamical parameters of 1.1.1.3.3.3-hexafluoropropanol-acceptor-systems systems in different solvents were determined by ir spectroscopy. Acetone, tetrahydrofurane, pyridine, alpha-picoline, 2.4.6-collidine and triethylamine were taken as acceptors and carbon tetrachloride and methylene chloride were used as solvents. The calculated equilibrium constants in carbon tetrachloride were found about four times higher than in methylene chloride. According to the basicity of the acceptor molecules the equilibrium constants increase in methylene chlorid as a solvents, but such effects are absent in the systems in carbon tetrachloride. In some cases result no straight lines plotting the ln K-values versus 1/T. In our oppinion the different ability of the two rotamers to form hydrogen bonds is responsible for these phenomena. An attempt was made for the explanation of the fourfold splitting of the association band in the systems with the fluorinated alcohol and pyridine in carbon tetrachloride. Some other solvents like n-hexane, chloroform, benzene and toluene were used in order to check the behaviour of the OH- signals of the investigated alcohol and to make a correct assignment between rotamers and bands.