Numerous carbon-13 chemical shifts of monosubstituted, meta- and para-disubstituted benzene derivatives as well as symmetrically and unsymmetrically substituted toluene and chlorobenzene homologs were measured to test the reliability of the simple sum rule from monosubstituted benzene derivatives. The chemical shifts of meta- and para-disubstituted benzene derivatives were examined with respect to the substituent constants σ_i and σ_π.