C-13 NMR AND AM1 STUDY OF THE INTRAMOLECULAR PROTON-TRANSFER IN SOLID 1,3-DIPHENYLPROPANE-1,3-DIONE

The intramolecular proton transfer reaction which takes place in solid 1,3-diphenylpropane-1,3-dione has been studied using a combination of 13C CPMAS NMR spectroscopy and AMI calculations. The splittings observed in the carbon signals, which are equivalent in solution, are interpreted in terms of a double minimum potential model, with the solution degeneracy of tautomers being lifted in the crystals. MO calculations suggest that the displacement of the equilibrium towards one of the tautomeric structures is due to conformational distortion upon crystallization.