INVESTIGATION OF B - HA REVERSIBLE B+H - A-EQUILIBRIUM IN COMPLEXES OF TRIFLUOROACETIC-ACID WITH PYRIDINES I DICHLOROMETHANE BY 2ND DERIVATIVE INFRARED-SPECTROSCOPY

The second derivative of FTIR spectra in the carbonyl-carboxyl region has been used in order to study the interaction of trifluoroacetic acid with eight R-pyridines in dichloromethane. In the case of the equimolar base-acid mixture, the following species (a) B . HA, (b) B . HA . HA, (c) B+H . A- and (d) B+H . A-.HA are recognized. All of the species are present in complexes of the medium strong pyridines (R = H or D, 3-Me and 4-Me). Two species (a) and (b) are found for complexes of the weakest, when R = 4-CN and 3-Br, and another two (c) and (d) for complexes of the strongest, when R = 3-NMe2 and 2,4,6-Me3, pyridines. Complete formation of the 1:1 complex requires an excess of pyridines. Fermi resonance of overtones due to pyridines and the acid with the continuous absorption is observed.