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1 Polish Journal of Chemistry

1 2003

1 Haeeb M.

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Critical behavior studies of 2,4-Dichlorobenzoic Acid-Amines Hydrogen-bonded Complexes Utilizing Fourier-Transform Infrared Spectroscopy

100%

Haeeb M.

tom Vol. 77 / nr 1

1-12

A series of crystalline 1:1 hydrogen-bonded complexes between 2,4-dichlorobenzoic acid (DCBA) and various quinolines and pyridines was prepared. Fourier-transform infrared spectra (FTIR) of these complexes are presented and analyzed in the _OH and _C=O regions. The correlation between the gravity center of the protonic vibrations _cg (cm-1), the quantity __/__0 and the pKa values of the amines are presented. The integrated intensities in solution A(Lmol-1 cm-2) and in the crystalline state A(kg mol-1 cm-2) in the _C=O region were correlated with the pKa values of the investigated amines. Striking anomalies are observed at the critical region (50% proton transfer). These results can be interpreted by assuming that quasi-symmetrical O..H..N bridge is formed with a single, flat minimum potential in the solid state and a double minimum potential in solution.