THE ROLE OF HYDROGEN-BOND LENGTH IN BRHPLN AND MEHPLN

A role of the geometrical effect was investigated based on the precise structure analyses of the isolated intramolecular hydrogen-bonded sys tem, h-BrHPLN, d-BrHPLN and MeHPLN. The hydrogen bond lengths (R(OO)) are almost identical for hydrogen and deuterium compounds of BrHPLN, a nd also in MeHPLN. This means that the geometrical effect is really su ppressed in the intramolecular hydrogen-bonded system. The reason why the BrHPLN system shows a large isotope effect on the phase transition s and MeHPLN does not may be ascribable to the difference in the natur e of the hydrogen bonds in each compound.