THE USE OF ANISOTROPIC C-13 CHEMICAL-SHIFTS TO STUDY THE SIDE-CHAIN CONFORMATION OF POLYCRYSTALLINE 2-METHOXYDIBENZOFURAN

Using the recently-developed 2D PHORMAT experiment, we have measured accurately and assigned the principal values of the thirteen C-13 chemical shift tensors in 2-methoxydibenzofuran, for which there is no published diffraction structure. A prediction of the conformation of the methoxy group, obtained by comparing the experimental principal values with the corresponding shieldings from ab initio calculations, agrees with a prediction based on the principal values of the unsubstituted parent compound dibenzofuran as modified with empirical methoxy substituent parameters. Both approaches indicate that the methoxy group has a cis conformation relative to the C-1 position, showing the potential of using chemical shift principal values to identify certain structural features of polycrystalline organic samples.