PROTON-TRANSFER AND CORRELATIONS BETWEEN THE C-O, O-H, N-H AND O-CENTER-DOT-CENTER-DOT-CENTER-DOT-N BOND LENGTHS IN AMINE PHENOLATES

A relationship between the geometrical parameters of the O-H...N bridg e based on the results of X-ray diffraction studies of a number of ami ne-phenol hydrogen-bonded complexes covering a broad Delta pK(a), rang e from -3.91 to 5.93 are proposed. The analysis shows that the shortes t bridges are realized when the proton transfer degree, reflected in t he C-O bond length, reaches about 50%. The position of the hydrogen at om is then close to the centre of the bridge. Such quasi-symmetric bri dges behave critically, being sensitive to temperature, pressure and d euteration. (C) 1997 Elsevier Science B.V.