INTERNAL AND EXTERNAL IMPLICATIONS OF THE STRUCTURE OF HYDROGEN-BONDED COMPLEXES .1. MNDO-PM3 AND AM1 STUDIES ON STRUCTURE OF 4-ACETYLPYRIDINE COMPLEX WITH PENTACHLOROPHENOL

The results of the PM3 and AM1 calculations of the hydrogen bonded sys tems resulting from pentachlorophenol and 4-acetylpyridine are compare d with X-ray data. The PM3 calculations properly reproduce the structu re of the complex contrary to AM1 which gives the hydrogen bridge geom etry different from the experimental one. The PM3 calculations show th at the repulsions between the components of the complex lead to seriou s nonlinearity of the bridge both in solid and in the gas phase. The c alculated potential for the rotation around H...N bond suggests that t he planarity found in the solid state structure results from the cryst al packing forces.