The orientational order parameters and approximate C-13 Shielding tensors of anthracene and of six of its 9,10-derivatives, 9,10-dihydroanthracene, 9,10-dimethylanthracene, 9,10-dibromoanthracene, anthraquinone, 9,10-diphenylanthracene, arid 9,10-bis(phenylethynyl)anthracene, dissolved in the nematic liquid crystal ZLI-1167 have been determined using a recently proposed C-13 NMR method. The biaxial order parameters obtained are compared with some current theoretical models of ordering. We find that none of these mean field approaches have fully satisfactory predictive capabilities.