X-ray structure of a trimeric 5,5 '-biaryl/erythro-beta-O-4-ether lignin model: Evidence for through-space weak interactions

The crystal structure of a trimeric lignin model 1 presenting the character istic pattern of biphenyl (5,5') and aryl-alkyl-ether (beta-O-4) linkages h as been determined. The crystal system is triclinic and the crystallographi c unit cell consists of two monomeric molecules. These results are compared with crystal data from the literature of simple models of the 5,5' and bet a-O-4 structure type. The availability of a terminal aldehyde function on t he model affords some interesting intermolecular interactions by weak hydro gen bonding which controls the conformation of the molecule and the aromati c ring orientation in particular; an unexpected cisoid conformation of the biaryl unit is observed based on the 64.4 degrees value found for the torsi on angle between the two 5,5' aromatic rings.