ORIENTATION OF THE CHEMICAL SHIELDING ANISOTROPY TENSOR OF THE CARBONATE CARBON IN DIPHENYL CARBONATE AND ITS CONSEQUENCES FOR NMR-STUDIES ON POLYCARBONATE

The orientation of the chemical shielding anisotropy tensor of the car bonate carbon in diphenyl carbonate was determined by using solid stat e NMR spectroscopy. The same tensor orientation was obtained from quan tum mechanical calculation based on density functional theory. The mos t shielded direction of the tensor is along the C=O double bond. The l east shielded direction is for the carbonate plane perpendicular to th e C=O double bond. Chemical shielding calculations in diphenyl carbona te fragments with different conformations show that the tensor orienta tion measured in crystalline diphenyl carbonate also applies to the ca rbonate groups of bisphenol A polycarbonate. However, this orientation is not identical to that assumed so far in the work on bisphenol A po lycarbonate. The consequences of this incorrect assumption in previous studies are examined.