Infrared studies of solvent effects on hydrogen bonding in some pyridine trifluoroacetates

Abstract

The i.r. spectra are reported for the trifluoroacetates of five substituted pyridines in five dry solvents of different activity with respect to proton transfer, aggregation, and triple ion effects. Four broad absorption regions (bands B–E) may be distinguished in the spectra. The intensity variation of these bands with solvent is very similar to that predicted by theory, and may provide evidence that the dipole of the hydrogen bond interacts with the reaction field from the environment. The shift of the centre of gravity, ν_H, as the reaction field increases can be explained either by a change of symmetry of the potential surface or by a change of hydrogen bond length. The centre of gravity, ν_H, is correlated with (ε– 1)/(2 ε+ 1) and E_T parameters and discussed with respect to specific and nonspecific interactions.